Basics of Animal Breeding and Genetics improvement

Basics of Animal Breeding and Genetics improvement
Lecture: BAHP I Semester I; September 2018 Bahame .B. David

Lecture outline Functions of animals Define Animal Genetics
Branches of genetics Genesis of animal genetics Population genetics Domestication Breeds development Animal breeding methods and systems

Course Requirements Read notes Also, use the following references:
1. Nicholas, F.W Introduction to veterinary Genetics. Oxford University Press. 2. Van Vleck, D.L., J.E. Pollak & E.A.B. Oltenacu Genetics for the Animal Sciences. W.H. Freeman & Company, USA. X VANV 3. Bourdon, R.M Understanding Animal Breeding. Prentice Hall International (UK) Limited, London. X BOU 4. Dalton, C An Introduction to Practical Animal Breeding. Collins, London (UK). X SF105 5. Animal breeding and improvement of farm animals by R A Brink

Functions of Animals Converting feed into food Clothing Power
80% of world’s population gets its protein, fat, iron, vitamins from animals (beef, poultry, pork, sheep etc) Clothing Fiber and skins for clothing production e.g wool, leather Power At one time, very important Recreation Horseback riding, racing, livestock shows & fairs

Functions of Animals Conservation By-products
Soil & soil fertility, animal manure in nutrient re-cycling and used as fuel By-products Bone, fat, blood etc important in manufacturing and food industries, pharmaceuticals etc

Genesis of Animal Genetics
Probably started before recorded history with domestication of animals Domestication may have been accidental in some cases In most cases, domestication was based on intentional selection for more friendly and tractable animals Behavioural traits are probably quantitative and involve many genes

Animal Genetics Is the study of the principles of inheritance in animals. Animal breeding is the application of the principles of animal genetics with the goal of improvement of animals. Terms often used interchangeably. Study and application of Animal Genetics involves several disciplines: Mendelian, Cytogenetics, Population, Quantitative & Molecular Genetics

Mendelian Genetics Has relatively little direct importance in animal improvement Principles are the basis of 2 specialized areas of genetics with major implications for animal improvement i.e. Population and Quantitative Genetics

Population Genetics Is simply, the study of Mendelian genetics in populations of plants & animals Basic foundation is the Hardy-Weinberg law Usually limited to inheritance of qualitative traits influenced by only a small number of genes Important to understand why characteristics, desirable or not, can be fixed or continue to exhibit variation in natural populations Principles applied to the design of selection strategies to increase the frequencies of desirable genes or elimination of deleterious genes

Genetics of Populations
Darwin didn’t understand how inheritance worked--Mendel’s work was still in the future. It wasn’t until the 1930’s when Mendelian genetics was incorporated into evolutionary theory, in what is called the “Neo-Darwinian synthesis”. Translated into Mendelian terms, the basis for natural selection is that alleles that increase fitness will increase in frequency in a population. Thus, the main object of study in evolutionary genetics is the frequency of alleles within a population. A “population” is a group of organisms of the same species that reproduce with each other. There is only one human population: we all interbreed. The “gene pool” is the collection of all the alleles present within a population. We are mostly going to look at frequencies of a single gene, but population geneticists generally examine many different genes simultaneously. Bahame.B.David (2013) Lecture Notes 27th April 2013

Allele and Genotype Frequencies
Each diploid individual in the population has 2 copies of each gene. The allele frequency is the proportion of all the genes in the population that is a particular allele. The genotype frequency of the proportion of a population that is a particular genotype. For example: consider the MN blood group. In a certain population there are 60 MM individuals, 120 MN individuals, and 20 NN individuals, a total of 200 people. The genotype frequency of MM is 60/200 = 0.3. The genotype frequency of MN is 120/200 = 0.6 The genotype frequency of NN is 20/200 = 0.1 The allele frequencies can be determined by adding the frequency of the homozygote to 1/2 the frequency of the heterozygote. The allele frequency of M is (p= P+1/2H) =0.3 (freq of MM) + 1/2 * 0.6 (freq of MN) = 0.6 The allele frequency of N is(q=Q+1/2H) = /2 * 0.6 = 0.4 Note that since there are only 2 alleles here, the frequency of N is 1 - freq(M). Bahame.B.David (2013) Lecture Notes 27th April 2013

Heterozygosity and Polymorphism
A gene is called “polymorphic” if there is more than 1 allele present in at least 1% of the population. Genes with only 1 allele in the population are called “monomorphic”. Some genes have 2 alleles: they are “dimorphic”. Heterozygosity is the percentage of heterozygotes in a population.. Bahame.B.David (2013) Lecture Notes 27th April 2013

Quantitative Genetics
Conceptually difficult because: Effects of individual genes can seldom be seen or measured Many genes are hypothesized to contribute to the expression of traits such as milk yield, growth rate or litter size. Further complicated by random influence of environment & other nongenetic factors

Quantitative Genetics
Very important from practical standpoint Most quantitative traits are economically important Have potential monetary value than simply inherited traits

Hardy-Weinberg Equilibrium
Early in the 20th century G.H. Hardy and Wilhelm Weinberg independently pointed out that under ideal conditions you could easily predict genotype frequencies from allele frequencies, at least for a diploid sexually reproducing species such as humans. For a dimorphic gene (two alleles, which we will call A and a), the Hardy-Weinberg equation is based on the binomial distribution: p2 + 2pq + q2 = 1 where p = frequency of A and q = frequency of a, with p + q = 1. p2 is the frequency of AA homozygotes 2pq is the frequency of Aa heterozygotes q2 is the frequency of aa homozygotes H-W can be viewed as an extension of the Punnett square, using frequencies other than 0.5 for the gamete (allele) frequencies. Bahame.B.David (2013) Lecture Notes 27th April 2013

THE HARDY WEINBERG PRINCIPLE
Calculating the gene frequencies from the genotype frequencies Easily done for codominant alleles (each genotype has a different phenotype) Bahame, (revised ppt) © 2008 Paul Billiet ODWS

to verify that the PRESENT population is in genetic equilibrium
Using the calculated gene frequency to predict the EXPECTED genotypic frequencies in the NEXT generation OR to verify that the PRESENT population is in genetic equilibrium Bahame, (revised ppt) © 2008 Paul Billiet ODWS

In general for an individual gene A and a .
Where the gene frequencies are p and q Then p + q = 1 and SPERMS A p a q EGGS AA p2 Aa pq aa q2 Bahame, (revised ppt) © 2008 Paul Billiet ODWS

THE HARDY WEINBERG EQUATION
So the genotype frequencies are: AA = p2 Aa = 2pq aa = q2 or p2 + 2pq + q2 = 1 Using the Hardy Weinberg Equation to determine the genotype frequencies from the gene frequencies may seem a circular argument Bahame, (revised ppt)

Hardy-Weinberg Example
Taking our previous example population, where the frequency of M was 0.6 and the frequency of N was 0.4. p2 = freq of MM = (0.6)2 = 0.36 2pq = freq of MN - 2 * 0.6 * 0.4 = 0.48 q2 = freq of NN = (0.4)2 = 0.16 These H-W expected frequencies don’t match the observed frequencies. Bahame.B.David (2013) Lecture Notes 27th April 2013

HOW MANY RATS IN UGANDA ARE CARRIERS FOR THE ALBINO ALLELE (Aa)?
a allele = = q A allele = p But p + q = 1 Therefore p = 1- q = 1 – 0.007 = or 99.3% The frequency of heterozygotes (Aa) = 2pq = 2 x x 0.007 = or 1.4% Bahame, (revised ppt) © 2008 Paul Billiet ODWS

Heterozygotes for rare recessive alleles can be quite common
Genetic inbreeding leads to rare recessive mutant alleles coming together more frequently Therefore outbreeding is better Outbreeding leads to hybrid vigour Bahame, (revised ppt) © 2008 Paul Billiet ODWS

Example: Rhesus blood group in Uganda
What is the probability of a woman who knows she is rhesus negative (rhrh) marrying a man who may put her child at risk (rhesus incompatibility Rh– mother and a Rh+ fetus)? Bahame, (revised ppt)

Rhesus blood group Rhesus positive allele is dominant Rh Frequency = p
Rhesus negative allele is recessive rh Frequency = q Frequency of rh allele = 0.4 = q If p + q = 1 Therefore Rh allele = p = 1 – q = 1 – 0.4 = 0.6 Bahame, (revised ppt) © 2008 Paul Billiet ODWS

Hardy Weinberg frequencies
Rhesus blood group Phenotypes Genotypes Hardy Weinberg frequencies Observed frequencies Rhesus positive RhRh p2 0.84 Rhrh 2pq Rhesus negative q2 0.16 Therefore, a rhesus negative, Ugandan woman in Uganda has an 84% chance of having husband who is rhesus positive… of which 36% will only produce rhesus positive children and 48% will produce rhesus positive child one birth in two Bahame, (revised ppt)

Predictable patterns of inheritance in a population so long as…
the population is large enough not to show the effects of a random loss of genes by chance events i.e. there is no genetic drift the mutation rate at the locus of the gene being studied is not significantly high mating between individuals is random (a panmictic population) new individuals are not gained by immigration or lost be emigration i.e. there is no gene flow between neighbouring populations the gene’s allele has no selective advantage or disadvantage Bahame, (revised ppt)

SUMMARY Genetic drift Mutation Mating choice Migration
Natural selection All can affect the transmission of genes from generation to generation Genetic Equilibrium If none of these factors is operating then the relative proportions of the alleles (the GENE FREQUENCIES) will be constant Bahame, (revised ppt)

II. Animal domestication
Symbiosis Definition: A biological situation in which at least two different kinds of organisms interact, the actors can include plants, animals, or plant and animal. The specific type of symbiosis between man and animal is termed mutualism. In this situation the two species benefit from each other. bahame; 2016

Domestication Selection for affinity to humans has been important with the dog than other species Dog is likely the first domesticated species Distinct breed types arose as <12000 years ago Dog probably derived from the wolf Only animal domesticated independently across the globe

Domestication In other domestic animals progressed very slowly for better performance primarily through better adaptation to the environment Most performance traits are quantitative Best example for performance is the horse Horses developed for draft and transportation of people

Domestication of animals is an example of a symbiotic relationship
Domestication of animals is an example of a symbiotic relationship. Man provides food and shelter to the animals, and they provide meat, mild, and fiber for man. Because of this relationship, both humans and domestic animals are secondary energy traps for the other; humans provide feed and care for the animals, while the animals provide draft power, meat, skins, milk. Fiber, etc.. bahame; 2016

What is a domestic animal
Definition: includes those animals whose breeding is or can be controlled be humans Excluding: zoo and circus animals, various rodents and primates, research animals, and animals caught wild and tamed. Does include reindeer. bahame; 2016

A domestic animal can not truly revert to being a wild animal.
Taming is on the path to domestication, but a tamed animal is not a domestic animal. Animals caught in the wild and tamed are not considered domesticated. Once they are bred in captivity and selected for particular qualities then they can be considered domesticated. A domestic animal can not truly revert to being a wild animal. Domestic animals that return to nature and breed are termed feral. bahame; 2016

When, where, why domesticate.
Hunters and gathers began domesticating animals through taming, but without any purposes other than for things they already knew: meat, skins, and bones. Through long experience and a decrease in the need for a nomadic lifestyle, many secondary uses of the animals were realized: milk, wool, power, etc.. bahame; 2016

A cultural revolution resulted as people were transformed from hunters and gathers to herders and cultivators. This is what started the modern civilization. The end of the glacial period marked the beginning of domestication. The glaciers began retreating 14,000 years ago. The full retreat was 11,000 years ago. bahame; 2016

People began harvesting wild grasses that were growing abundantly and storing them. At this point in history, people could not leave for long periods of time for fear someone could come along and loot their food sources. This is what led to small villages being formed. This gradually changed the culture to what it is today. bahame; 2016

More animals had to be domesticated for personal food supply.
Women no longer had to spend as much time gathering food. This increased birth rate and decreased infant mortality. Men now had to always hunt near the villages, which resulted on over hunting in some areas. More animals had to be domesticated for personal food supply. Slowly, the human became more of a farmer and less of a hunter. bahame; 2016

Robert Bakewell 1700s Used inbreeding progeny testing
English Breeder of: Shire horses Leicester sheep Longhorn cattle Used inbreeding progeny testing

Gregor Mendel basic genetic principles used pea plants
not well understood during his life Mendel, G Experiments on Plant Hybridization. Transactions of the Brünn Natural History Society.

Charles Darwin British naturalist natural selection as an evolutionary
force Darwin, C The Origin of Species by Means of Natural Selection.

Sewell Wright Zoologist USDA University of Chicago
University of Wisconsin Wright, S An intensive study of the inheritance of color and other coat characters in guinea pigs. Carnegie Institution of Washington: Pub. No. 241:59 Evolution and the Genetics of Populations. Sewell Wright Vol 1: Genetic and Biometric Foundations. (1968) Vol 2: Theory of Gene Frequencies. (1969) Vol 3: Experimental Results and Evolutionary Deductions. (1977 Vol 4: Variability Within and Among Natural Populations. (1978)

Ronald Fisher English Statistician provided statistical
basis of inheritance R. A. Fisher The genetical theory of natural selection. Dover Publications

Jay Lush founder of science of Animal Breeding Iowa State University
1930s to 19 70s Lush, J.L The number of daughters necessary to prove a sire. J. Dairy. Sci 14:209 Lush, J.L The Genetics of Populations. (published after his death)

Evolution of Livestock Breeds
How do breeds adapt and change? What is their history? Why does it matter? Lect ii

I. What is a breed? A. Animals that, through selection and breeding, have come to resemble one another and pass those traits uniformly to their offspring. 1. Unfortunately this definition leaves some unanswered questions. For example, when is a crossbred animal considered a composite breed and when do we stop thinking about them as composites? The Genetics of Populations by Jay L. Lush helps explain why a good definition of "breed" is elusive. a. A breed is a group of domestic animals, termed such by common consent of the breeders, ... a term which arose among breeders of livestock, created one might say, for their own use, and no one is warranted in assigning to this word a scientific definition and in calling the breeders wrong when they deviate from the formulated definition. It is their word and the breeders common usage is what we must accept as the correct definition. 2. Dr. Lush's definition helps us understand that it is at least in part the perception of the breeders and the livestock industry which decides when a group of individuals constitutes a "breed".

I. What is a breed? Breeds are primarily distinguished by visual characteristics: color, pattern, polled or horned condition, or extreme differences in form and shape. Composite or synthetic breeds: new breeds being developed that combine the desirable characteristics of several existing breeds. Purebred: purity of ancestry; only animals in that particular breed have been mated to produce the animal in question.

II. Breed Development The development or evolution of breeds can take different routes. Sometimes, change that can occur as the result of selection for a small number of traits Holstein cattle have been selected primarily for milk production and are the highest milk producing cattle in the world. The Bedouins of the desert developed Arabian horses with strength, courage and stamina required for survival, and for the speed and responsiveness needed to win the tribal skirmishes.

II. Breed Development 2. Other breeds have traits that result from natural selection pressure based upon the environment in which they were developed. N’dama cattle from West Africa have, through the centuries, developed a resistance to trypanosomiasis or sleeping sickness spread by the tse-tse fly, which is fatal to most other breeds of cattle. The Chincoteague Pony descended from the feral horses on a barrier island off the coast of Maryland and Virginia. 80% of their diet is coarse saltmarsh cordgrass and American beachgrass; their diet also includes poison ivy. The high concentration of salt in their diets causes the horses to drink twice as much fresh water as domestic horses and have a "bloated" appearance.

II. Breed Development B. Adaptations of an animal determine its niche in the environment. Adaptation: evolution of structural, internal, or behavioral features that help an organism better survive in an environment. a. The large eyes of nocturnal animals. Niche: the role of a particular species in a community regarding food, space, reproduction, etc.

II. Breed Development 3. Structure and Behavior Determine Environment
a. Structure 1. Sharks have characteristics that enable them to survive in water, a streamlined body design and teeth that re-grow to replace broken ones. 2. The artic fox’s coat changes color for camouflage. b. Behavior 1. Bears survive a long, cold winter by hibernating. 2. Pigs are difficult to herd and move long distances, so they are used mostly in farming communities.

II. Breed Development C. Livestock have evolved over time through genetic changes that are both natural and selected by man. Mutation: random error or change in the DNA sequence that may effect whole chromosome or one gene. a. This usually results in a negative result. Natural Selection: a mechanism that explains how populations evolve; organisms with favorable variations survive. a. The Romney breed of sheep respond to it’s geographic and climatic conditions with hooves that are resistant to foot rot and fleeces that remain healthy in harsh weather.

II. Breed Development 3. Reproductive Isolation: occurs when organisms that formerly interbred are prevented from producing offspring. By developing different mating times. By geographic factors This is often induced by man. D. All these factors can lead to a new breed or even a new species

III. Why is biodiversity important?
A. Why are we concerned about preserving information about minor, or relatively unknown, breeds of livestock?

Holstein cow example Holstein has advantage over other breeds in the production of whole milk, this advantage is based on feeding high levels of cereal grains and pricing that favors low milk-solids content. The Dutch Belted breed displayed excellent milking ability in a grass-based dairy situation in trials in the early 1900s and would be more preferable if cereal grains weren’t available. In Australia, composite breeds, such as the Australian Friesian Sahiwal, have been developed which have higher milk production levels than Holsteins in the tropical regions of that country.

2. Natural resistance to diseases or parasites example Some breeds of sheep have a natural resistance to internal parasites. Should vaccines become restricted or uneconomical, then a breed such as the critically endangered Gulf Coast Native, with the parasite resistance it has developed through natural selection, could be of critical importance in the sheep industry.

B. Genetic diversity should be maintained to help meet the potential challenge resulting from changes in production resources and market requirements.

Animal breeding and genetics
Science deals with physiology of heredity i.e mechanism by which resemblance between parents and offspring is conserved and transmitted Mechanism by which resemblance is modified and transformed explain how heredity characters of individuals are represented in eggs and sperm Bahame.B.David (2013) Lecture Notes 27th April 2013

Animal breeding and genetics
Animal breeding is a branch of animal science that addresses the evaluation of the genetic value (estimated breeding value, EBV) of domestic livestock. Selecting animals for breeding with superior EBV in growth rate, egg, meat, milk, or wool production, or have other desirable traits Bahame.B.David (2013) Lecture Notes 27th April 2013

Some are pure breeds others non-pure breed
A population is a group of interbreeding individual- i.e a breed or strain within a breed Some are pure breeds others non-pure breed Selective breeding utilizes the natural variation in traits that exist among members of any population Breeding progress require understanding the two sources of variation; genetics and environment Bahame.B.David (2013) Lecture Notes 27th April 2013

Animal’s genotype provides the genetic background for its phenotype
Animal breeders are concerned with changing animal populations genetically but use most desirable genotype Animal’s genotype provides the genetic background for its phenotype P= G+E, P= phenotype, G= genotype, E= environmental effects The environmental effect is the external factors that are non-genetic, have effect on animal performance Bahame.B.David (2013) Lecture Notes 27th April 2013

Animal phenotype is determined by its genotype and environment it experiences
Genotype is gene combination that affect the array of traits of interest Tropically adapted genotype –include all the genes, gene combination affecting heat resistance, parasite resistance and any other traits make up tropical adaption Animal with similar genotype are said to be having same biological type Bahame.B.David (2013) Lecture Notes 27th April 2013

Analyzing the breeding system
System- group of interdependent component part Analyzing breeding system considering ‘What is the best animal?’ What traits are of primary importance and what phenotype and genotype are most desirable for those traits i.e Beef cattle breeders look at easy calving, much growth as possible for birth weight and moderate milk Bahame.B.David (2013) Lecture Notes 27th April 2013

Consider a single farm as a breeding system
Component of this system are categorized as Animals (genotype) Physical environment Fixed resource and management Economics Animals category Contain characteristic genotype On dairy farm e,g tropical genotype described as having small size, low feed intake, moderate yield and high butter content Bahame.B.David (2013) Lecture Notes 27th April 2013

Contrasting genotype is described as large size, high feed intake, high yield and low butter fat etc
Physical environment Things that human exert little control like weather, altitude, soils, quality and quantity of native forages e.g range cattle and sheep exist under condition little different from their wild ancestors Dairy cattle, hogs, pets that are confined indoors and feed on harvested feeds are insulted from nature so perform better Bahame.B.David (2013) Lecture Notes 27th April 2013

Fixed resources and management
Farm size, ability of farm to grow, supplementary feeds and available labour Management Involves all the policies implemented by the farmer e.g level of supplementary feeding, health care and length of time animals remain of farm Economics Refers to costs of farm inputs like feed, labour, and supplies and the price for farm outputs(animals themselves) Bahame.B.David (2013) Lecture Notes 27th April 2013

Therefore genotype depends on local environment, management practices in use, costs of inputs and prices of animal product. Genotype by environment interaction occurs when the differences in performance between 2 or more genotype changes from environment to environment (i.e physical environment, management, economics and fixed resources Bahame.B.David (2013) Lecture Notes 27th April 2013

Example of genotype versus environment interaction is about animals that are adapted to temperate location versus animals that are adapted to tropical areas In temperate environment, temperately adapted genotype out perform the tropically adapted genotype but both perform quite well Bahame.B.David (2013) Lecture Notes 27th April 2013

Tropical environment is considered more stressful due to extreme heat, humidity, insects and other parasites and both genotype produce at a lower level But loss in productivity is much less for tropically adapted genotype than for the temperately adapted genotype This is because the tropically adapted type is genetically resistant to heat and parasite Bahame.B.David (2013) Lecture Notes 27th April 2013

Breeding stock or seed stock
"Breeding stock" is a term used to describe a group of animals used for purpose of planned breeding. Individuals looking to breed animals look for certain valuable traits in purebred animals, or may intend to use some type of crossbreeding to produce a new type of stock with different, and presumably superior abilities in a given area of endeavor Bahame.B.David (2013) Lecture Notes 27th April 2013

For example, when breeding swine the "breeding stock should be sound, fast growing, muscular, lean, and reproductively efficient And subjective selection of breeding stock" in horses has led to many horse breeds with particular performance traits e.g how fast is the horse Beef cattle breeders look at easy calving, much growth as possible for birth weight and moderate milk etc Bahame.B.David (2013) Lecture Notes 27th April 2013

Pure breeding Mating animals of the same breed for maintaining such breed is referred to as purebred breeding. Opposite to the practice of mating animals of different breeds, purebred breeding aims to establish and maintain stable traits, that animals will pass to the next generation. Bahame.B.David (2013) Lecture Notes 27th April 2013

By "breeding the best to the best," employing a certain degree of inbreeding, considerable culling, and selection for "superior" qualities, one could develop a bloodline or "breed" superior in certain respects to the original base stock. Bahame.B.David (2013) Lecture Notes 27th April 2013

An individual who results from inbreeding is referred to as inbred.
inbreeding is reproduction from the mating of parents who are closely related genetically. Inbreeding results in increased homozygosity, which can increase the chances of offspring being affected by recessive or deleterious traits. This generally leads to a decreased fitness of a population, which is called inbreeding depression. An individual who results from inbreeding is referred to as inbred. Bahame.B.David (2013) Lecture Notes 27th April 2013

The degree of inbreeding can be estimated from the number of males and females available for breeding ∆ F is the increase in % inbreeding per generation N is the number of breeding animals in the population (group) It is advisable to keep ∆ F below 1%. Bahame.B.David (2013) Lecture Notes 27th April 2013

The avoidance of expression of deleterious recessive alleles caused by inbreeding is thought to be the main selective force maintaining the out-crossing aspect of sexual reproduction Livestock breeders often practice controlled breeding to eliminate undesirable characteristics within a population, which is also coupled with culling of what is considered unfit offspring, especially when trying to establish a new and desirable trait in the stock Bahame.B.David (2013) Lecture Notes 27th April 2013

Inbreeding may result in a far higher phenotypic expression of deleterious recessive genes within a population than would normally be expected. First-generation inbred individuals are more likely to show physical and health defects, including: Reduced fertility both in litter size and sperm viability, Increased genetic disorders, Fluctuating facial asymmetry, Lower birth rate, Higher infant mortality, Slower growth rate, Smaller adult size, Loss of immune system function Bahame.B.David (2013) Lecture Notes 27th April 2013

The reduced genetic diversity that results from inbreeding may mean a species may not be able to adapt to changes in environmental conditions. Each individual will have similar immune systems, as immune systems are genetically based. Where a species becomes endangered, the population may fall below a minimum whereby the forced interbreeding between the remaining animals will result in extinction Bahame.B.David (2013) Lecture Notes 27th April 2013

Domestic animals breeding in domestic animals is assortative breeding primarily (selective breeding). sort individuals by trait, to establish a breed, to remove poor genetic material. Homozygosity is the case where similar or identical alleles combine to express a trait that is not otherwise expressed (recessiveness). Bahame.B.David (2013) Lecture Notes 27th April 2013

Selective breeding (also called artificial selection) is the process by which humans breed other animals and plants for particular traits. Typically, strains that are selectively bred are domesticated, and the breeding is sometimes done by a professional breeder. Bred animals are known as breeds The cross of animals results in what is called a crossbreed, and crossbred plants are called hybrids Bahame.B.David (2013) Lecture Notes 27th April 2013

In animal breeding; techniques such as in-breeding, line-breeding, and out-crossing are utilized for selection Selection is the systematic choice of animals in a population as parents for the next generation. Population is defined in the genetic sense as a group of interbreeding animals sharing a common gene pool, e.g. a closed herd, an AI district, a breed) Bahame.B.David (2013) Lecture Notes 27th April 2013

Family selection means the selection of individuals on the performance of their relatives (sibs, half-sibs, or progeny), i.e. selection between families instead of between individuals.(phenotypic selection) Genotypic selection is that based on progeny testing with a very large number of progeny, so that the breeding value of the parent is exactly known Bahame.B.David (2013) Lecture Notes 27th April 2013

Methods of selection Types of selection individual or mass selection,
within and between family selection, sibling selection, and progeny testing, with many variations. Within family selection uses the best individual from each family for breeding. Between family selection uses the whole family for selection. Mass selection uses records of only the candidates for selection. Bahame.B.David (2013) Lecture Notes 27th April 2013

Mass selection is most effective when heritability is high and the trait is expressed early in life, in which case all that is required is observation and selection based on phenotypes. All the types of selection are under Artificial selection which is under human control has two aspects i.e replacement selection and culling Replacement you decide which animal to become parent for the first time Bahame.B.David (2013) Lecture Notes 27th April 2013

selection Selection for simply inherited traits
These are traits controlled by few genes Selection is based on pedigree and progeny information Selection for polygenic traits Traits controlled by many genes and no single gene has an overriding effect over the other Selection based on phenotypic performance, prediction of breeding value, accuracy value, Bahame.B.David (2013) Lecture Notes 27th April 2013

In domesticated animals.
Inbreeding is used to reveal deleterious recessive alleles, which can then be eliminated through assortative breeding or through culling In-breeding is used to fix desirable genetic traits within a population or to attempt to remove deleterious traits by allowing them to manifest phenotypically from the genotypes. Bahame.B.David (2013) Lecture Notes 27th April 2013

Inbreeding is defined as the use of close relations for breeding such as mother to son, father to daughter, brother to sister. Linebreeding is a form of inbreeding. There is no clear distinction between the two terms, but line breeding may encompass crosses between individuals and their descendants or two cousins Bahame.B.David (2013) Lecture Notes 27th April 2013

Line breeding -This method can be used to increase a particular animal's contribution to the population is less likely to cause problems in the first generation than does inbreeding, But over time, can reduce the genetic diversity of a population and cause problems related to a too-small gene pool that may include an increased prevalence of genetic disorders and inbreeding depression. Bahame.B.David (2013) Lecture Notes 27th April 2013

Outcrossing is where two unrelated individuals have been crossed to produce progeny.
In outcrossing, unless there is verifiable genetic information, one may find that all individuals are distantly related to an ancient progenitor. If the trait carries throughout a population, all individuals can have this trait. Bahame.B.David (2013) Lecture Notes 27th April 2013

1. single crossing (two-way crossing) of two breeds;
The following crossbreeding systems will be discussed for the production of hybrid animals: 1. single crossing (two-way crossing) of two breeds; 2. criss-crossing of two breeds (rotational crossbreeding); 3. three-way crossing (three breeds); 4. criss-crossing of three breeds (rotational crossbreeding); 5. four-way crossing (double-cross) with four breeds. Bahame.B.David (2013) Lecture Notes 27th April 2013

Other terms that are used to indicate breeding systems are: -
- Back crossing; mating a crossbred to one of the parent breeds again - Upgrading: systematic back crossing with the improved breed - Interbreeding; mating hybrids to form a new breed - Assortative mating (mating alikes) and/or mating unlikes (negative assortative mating). Bahame.B.David (2013) Lecture Notes 27th April 2013

Hybrid vigour (Heterosis), usually demonstrated by
increase in size, better live weight gains and greater resistance to disease and in the earlier attainment of sexual maturity, occurs in the first cross-bred generation out of the mating of 2 widely dissimilar pure-bred parental stocks. Hybrid vigour is an indication of heterozygosis. Bahame.B.David (2013) Lecture Notes 27th April 2013

Determining sex for sperm as a means of breeding system
The offspring performance of hybrids exceeds the average performance of the parent breeds Determining sex for sperm as a means of breeding system E.g, a producer may want female calves from the best cows for replacements and male calves for beef production. Dairy producers may want more females for replacing cows or for expansion of their herds. Bahame.B.David (2013) Lecture Notes 27th April 2013

Breeding objectives Breeding objectives is changing the genetic makeup of a population of animals, where population is defined as a recognized breed The breeding goals are dictated by market demand; Sometimes the market place demands a different product than was defined as desirable in the original breeding objective (adjust breeding program) Breeding methods depend on heritability and genetic correlations for desirable traits. Bahame.B.David (2013) Lecture Notes 27th April 2013

Genetic correlation occurs when a single gene affects two traits.
many genes may affect two or more traits. Genetic correlations can be positive or negative, it ranges from +1 to − 1, with 0 indicating no genetic correlation. +1 means that the traits always occur together, while a correlation of − 1 means that having either trait always excludes having the other trait. Bahame.B.David (2013) Lecture Notes 27th April 2013

Positive correlation For example, selecting for increased milk production also increases protein production. or selection for increased weight gain in broiler chickens, which also increases the fat content of the birds. Negative correlation For example, as milk production is increased in dairy cows through genetic selection, it is slightly more difficult for the high-producing cows to conceive. selecting for improved fertility may result in a reduction in milk production or its rate of gain Bahame.B.David (2013) Lecture Notes 27th April 2013

Breeding objectives and industry structure
Breeding industry is thought of as a pyramidal structure A few elite breeders at top selling breeding stock to a large group of multipliers who sell animals to greater many end users Pyramid suggests flow of germ plasma -genetic material in form of Live animal Semen Embryo from top to bottom Bahame.B.David (2013) Lecture Notes 27th April 2013

Livestock Breeding sector
Seedstock Producers (breeders- parent stock) Produces animals for breeding purposes Sire producing herds Dam producing herds

Commercial Producers Animals are intended for entering the food chain. Many times buy herd sires May or may not produce replacement females. Eg beef production,eggs,broilers, milk, pork etc

Pyramid structure ELITE BREEDERS MULTIPLIERS END USERS/COMMERCIAL
Consumers Bahame.B.David (2013) Lecture Notes 27th April 2013

(end users/society) FOR MORE INFO... Chapter 1, pg. 11 – 14. Understanding Animal Breeding. Text book

Elite breeders produce most advance animals
Multipliers multiply the animals End users benefit from genetic improvement occurring at higher level Each level produce animals that will be of greatest demand by the customers at level down End user –individual whose particular needs should form the basis for determining breeding objectives for breeding stock Bahame.B.David (2013) Lecture Notes 27th April 2013

Elite Breeders May or may not be hobby breeders Breeds registry and nomecliture Size of operation varies Use of advanced technology AI, ET, cloning

Multipliers Dedicated Producers Livelihood Size of operation varies Innovation and Technology transfer Use of advanced technology AI, ET, cloning - ?

Livestock Breeding Industry
End Users May or may not be primary get income Size of operation varies Limited in use of technology Consumers of the products

Traditional livestock species
Food and fiber producing species (sheep, cattle, swine and poultry) the end user are commercial producers Commercial producers- breeders whose primary product is a commodity for public consumption Commercial dairy operations produce milk, Commercial sheep operation produce lamb, mutton, and wool Bahame.B.David (2013) Lecture Notes 27th April 2013

Commercial swine operation produce pork
Commercial poultry operation produce eggs, chicken and turkey Commercial cattle producer produce beef Commercial producers may not be end user they can be middlemen such as Feedlot operators Packing companies Retailers -Commercial producers can be end user because their needs reflect the requirements of the entire industry Bahame.B.David (2013) Lecture Notes 27th April 2013

Seed stock producers provide stock for commercial producers
If commercial producers are end users at the bottom of pyramid then the elite and multipliers are seed stock producers Seed stock- breeding stock, animals whose role is to be a parent or to contribute gene to the next generation Seed stock producers provide stock for commercial producers Seed stock producers produce best animals- depends on needs Bahame.B.David (2013) Lecture Notes 27th April 2013

Factors that distort breeding objectives
E.g emphasis placed by breeders of meat and dairy animals on particular spotting patterns or shades of coat colour- coat colour has little to do with production efficiency What cause distorted breeding objectives? Competition among breeders Undue reliance on the end users upon the opinion of breeders higher up in the pyramid Bahame.B.David (2013) Lecture Notes 27th April 2013

Mating and Mating systems
Two basic tool used by breeders to make genetic change Selection mating Mating is the process that determines which(selected) males are bred to which females selection you choose animals to be parents, in mating you match males and females from selected group Bahame.B.David (2013) Lecture Notes 27th April 2013

Mating systems follow mating rules
Large to large- producer extreme Large to small- produce intermediate Charolais to angus- produce hybrid Half brother to half sister- produces an inbred Mating system depends on results wanted 3 reasons why breeders use mating systems Produce offspring with extreme breeding value to increase rate of genetic change Bahame.B.David (2013) Lecture Notes 27th April 2013

To make use of complementarity
To obtain hybrid vigor Complementarity- an improvement in the overall performance of offspring Complementarity results from mating individuals with different but complementary breeding values Bahame.B.David (2013) Lecture Notes 27th April 2013

Bahame.B.David (2013) Lecture Notes
27th April 2013

Calculate the resulting hybrid vigor on percentage basis.
Example: cross breeding between two dairy breeds: Average milk production per year of breed A is 8000kgs, Average milk production per year of breed B is 6000kgs, Average of cross bred cow is 7500kgs. Calculate the resulting hybrid vigor on percentage basis. Let kgs+6000kgs =7000kgs Therefore %HV = X100% =7.14% 2 7000 Bahame.B.David (2013) Lecture Notes 27th April 2013

Bahame.B.David (2013) Lecture Notes
27th April 2013

METHODS OF SELECTION FOR MORE THAN ONE TRAIT
select for more than one trait at a time. The desired traits will depend upon their economic value, but only those of real importance should be considered. If too many traits are selected for at one time, less progress will be made in the improvement of any particular one Bahame.B.David (2013) Lecture Notes 27th April 2013

Several methods may be used for determining which animal should be saved and which should be rejected for breeding purposes. Tandem Method selection is practiced for only one trait at a time until satisfactory improvement has been made in this trait. Selection efforts for this trait are then relaxed, and efforts are directed toward the improvement of a second, then a third, and so on- least efficient method The efficiency of this method depends a great deal upon the genetic association between the traits selected for Bahame.B.David (2013) Lecture Notes 27th April 2013

Independent culling Method
selection may be practiced for two or more traits at a time, but for each trait a minimum standard is set that an animal must meet in order for it to be saved for breeding purposes. The failure to meet the minimum standard for anyone trait causes that animal to be rejected for breeding purposes. It is also used when a particular color or color pattern is required Bahame.B.David (2013) Lecture Notes 27th April 2013

The Selection Index Method
involves the separate determination of the value for each of the traits selected for, and the addition of these values to give a total score for all of the traits. animals with the highest total scores are then kept for breeding purposes. influence of each trait on the final index is determined by how much weight that trait is given in relation to the other traits. The amount of weight given to each trait depends upon its relative economic value, since all traits are not equally important upon the heritability of each trait the genetic associations among the traits. Bahame.B.David (2013) Lecture Notes 27th April 2013

Some indexes are used for selection between individuals,
The selection index is more efficient than the independent culling method, for it allows the individuals that are superior in some traits to be saved for breeding purposes even though they may be slightly deficient in one or more of the other traits. Some indexes are used for selection between individuals, others for selection between the progeny of parents from different kinds of matings, such as line-crossing and crossbreeding, others for the selection between individuals based on the merit of their relatives, as in the case of dairy bulls, where the trait cannot be measured in that particular individual. Bahame.B.David (2013) Lecture Notes 27th April 2013

Breeding value Breeding value is defined as the value of an individual as a parent. Parents transfer a random sample of their genes to their offspring. Estimated breeding value gives an estimate of the transmitting ability of the parent. Breeding value of parent is a key ingredient determining progeny breeding value and performance Animal’s breeding value for mature weight is the sum of the independent effects of that animal’s genes Bahame.B.David (2013) Lecture Notes 27th April 2013

Parent transmit half of their genes to their offspring –one gene/allele from each pair of genes at a locus Segregation and independent assortment of genes prevent inheritance of gene combination Then breeding value reflect only the sum of effects of independent genes effects not gene combination effects Bahame.B.David (2013) Lecture Notes 27th April 2013

Progeny difference or transmitting ability
Is Half an individual breeding value- the expected difference between the mean performance of the individual’s progeny and mean performance of all progeny (assuming random selected mates) PD = ½ BV PD is not directly measurable like breeding value but can be predicted from performance data so can be called Expected progeny differences(EPDs); predicted differences(PDs); or estimated transmitting abilities (ETAs) Bahame.B.David (2013) Lecture Notes 27th April 2013

Expected Progeny Difference
One-half the estimated breeding value is equal to the Expected Progeny Difference (EPD)= 1/2EBV Thus, EPDs compare or rank the superiority of individual animals. EPDs provide a prediction of future progeny performance of one individual compared to another individual within a breed for a specific trait. Bahame.B.David (2013) Lecture Notes 27th April 2013

The EPDs are reported in plus or minus values in the units of measurement for the trait.
For example, birth, weaning and yearling weight EPDs are reported in pounds. The EPD values may be used to compare only those animals within a breed. Bahame.B.David (2013) Lecture Notes 27th April 2013

Additive properties of breeding value and progeny difference
Animal’s breeding value or progeny difference for a traits is a function of the independent effects of the animal’s genes influencing a trait These genes are additive so breeding value is the sum of independent effects of all the animal’s genes influencing the trait Breeding value is additive genetic gene effects or additive value BVoffspring = 1/2BV sire + 1/2BV Dam Bahame.B.David (2013) Lecture Notes 27th April 2013

Gene combination value (GCV)
Is part of individual’s genotypic value that is due to effects of gene combination (dominance and epistasis) and not transmitted from parent to offspring Breeding value is part of genotypic value that is transmitted from parent to offspring Remaining portion of genotypic value is called gene combination value Animal’s breeding value and gene combination constitute its genotypic value for a trait; G= BV+GCV Bahame.B.David (2013) Lecture Notes 27th April 2013

Gene combination effects are non additive gene effects
Gene combination effects are not additive like independent gene effects Gene combination effects are non additive gene effects GCVoffspring ≠ 1/2GCVSire + 1/2GCVDam Independent gene effects are effects of a gene independent of the effects of the other gene at the at the same locus (dominance) and effects of genes at other loci (epistasis) Bahame.B.David (2013) Lecture Notes 27th April 2013

Permanent and temporary environmental effects
Producing ability is a function of all those factors that affect an individual performance potential Genotypic value and gene combination are determined at conception so are permanent effects Environmental effects that influence an animal’s performance for repeated traits are permanent environmental effects(Ep) Producing ability; PA= G +Ep And because G= BV+GCV Bahame.B.David (2013) Lecture Notes 27th April 2013

Therefore PA= BV+GCV + Ep
Producing ability is neither purely genetic nor purely environmental on but a combination of both Effects that do not permanently influence animal’s performance potential are temporary environmental effects Temporary environmental effects affect animal’s performance a single time, not all the time Bahame.B.David (2013) Lecture Notes 27th April 2013

Importance of producing ability
It is important to commercial producers An animal can be fed according to the producing ability usually called most probable producing abilities(MPPAs); calculated from performance data Producing ability is less important to seed stock breeders Seed stock producers think of breeding value Bahame.B.David (2013) Lecture Notes 27th April 2013

What is a Breeding Index?
Whilst EBVs aid the selection of breeding stock according to specific traits they can also be combined into selection indexes to meet wider breeding objectives. An index is an overall score of genetic merit combining the relative economic values of several EBV traits Bahame.B.David (2013) Lecture Notes 27th April 2013

five selection indexes:
Beef Value: The economic value of an animal in terms of the financial merit of its offsprings’ carcases Calving Value: The economic value of an animal in terms of gestation length and difficult calvings Maternal Value: The economic value of an animal’s genetic ability to produce breeding females Bahame.B.David (2013) Lecture Notes 27th April 2013

Maintenance Value: The economic cost associated with mature size
Maternal Production Value: The economic value of an animal’s ability to produce breeding females and beef carcase characteristics, calculated from the four values listed above The EBVs accounted for in the calculation of these indexes is shown below: Bahame.B.David (2013) Lecture Notes 27th April 2013

Heritability and Repeatability
Heritability tells us to what extent the differences observed in animal performance are due to inheritance Also is a measure of the degree of which offspring resemble their parent in performance for a trait In High heritable trait parent produce offspring that show high performance In Low heritable trait performance of parent show little about progeny performance Bahame.B.David (2013) Lecture Notes 27th April 2013

In animal breeding heritability is the measure of strength (consistency, reliability) of the relationship between performance (phenotypic value) and breeding values for a trait in a population High heritability, breeding values have large influence on phenotypic value In high heritable traits the performance of animal reveals a lot about their breeding values and vice versa for low heritable traits Bahame.B.David (2013) Lecture Notes 27th April 2013

Heritability is denoted h2 it is a square of correlation between phenotypic value and breeding value, h2=r2P,BV- narrow sense Broad sense heritability (H2), is a measure of the strength of the relationship between performance (phenotypic value) and genotypic values for a trait in a population H2 =r2P,G H2 measures the total influence of genetics on the expression of a trait because it includes contribution of both breeding value and gene combination values –not helpful measure Bahame.B.David (2013) Lecture Notes 27th April 2013

Heritability is positive ranges from 0 to +1 or 0-100%
Zero means not heritable and 1 highly heritable Any trait below 0.2 are considered lowly heritable; 0.2 to 0.4 moderately heritable traits and above 0.4 highly heritable Heritability varies from population to population and environment to environment High heritability indicate there is a strong relationship (strong correlation) between phenotypic values and breeding values for a trait Bahame.B.David (2013) Lecture Notes 27th April 2013

Heritability and resemblance among relatives
Individuals with traits with high heritability relatives tend to resemble each other in the trait – performance Individuals with traits with low heritability -there is little resemblance among relatives in the traits When heritability is high there is strong relationship between observed performance and breeding value; phenotypic values and breeding value are highly correlated Bahame.B.David (2013) Lecture Notes 27th April 2013

Importance of heritability
It is important in selection for polygenic traits Choose animals with best breeding values to become parents -need for records Phenotypic selection you use individual performance to select animals Bahame.B.David (2013) Lecture Notes 27th April 2013

Repeatability Is a measure of the strength (consistency, reliability) of the relationship between repeated records (repeated phenotypic values) for a trait in a population Examples are milk yield in dairy animal, racing and show performance in horses, litter size in swine, and fleece weight in sheep Environment can change the repeated record for a trait Bahame.B.David (2013) Lecture Notes 27th April 2013

1 and 2 refer to two different records for same individuals
Repeatability can be defined as a measure of the strength (consistency, reliability) of the relationship between single performance records (phenotypic value) and producing ability for a trait in a population High repeatability of a single record of performance can be a good indicator of producing ability r = rP1P2 1 and 2 refer to two different records for same individuals Bahame.B.David (2013) Lecture Notes 27th April 2013

Repeatability ranges from -1 to +1 though rarely are trait negative
r =r2P,PA Repeatability ranges from -1 to +1 though rarely are trait negative Repeatability near 1 indicates that the trait is extremely repeatable and near zero shows that the trait hardly repeatable Below 0.2 the traits are lowly repeatable and between 0.2 and 0.4 are considered moderately repeatable and above 0.4 are highly repeatable. Bahame.B.David (2013) Lecture Notes 27th April 2013

Importance of repeatability Useful in making culling decision
Repeatability varies from population to population and environment to environment Importance of repeatability Useful in making culling decision Bahame.B.David (2013) Lecture Notes 27th April 2013

Performance Recording for Genetic Evaluation “The Benefits
What are the benefits? • Receive a sophisticated report for your herd which includes Estimated Breeding Values (EBVs) for your sires, dams, heifer progeny, bull progeny and steer progeny. It also contains genetic trends for your herd benchmarked against the breed average Effective identification of animals with the best genetic package for you and your bull buying clients (in the case of bull breeders). It enables you to identify and select against the normal trait antagonisms. For example increase growth and muscling, while maintaining or increasing marbling • Bahame.B.David (2013) Lecture Notes 27th April 2013

BREEDPLAN is a modern genetic evaluation system for beef cattle.
Monitor the genetic progress of your herd across a range of economically important traits. This allows you to identify how your selections are impacting on your herd’s genetic progress for a range of traits. • Access to other genetic tools that assist selection and genetic progress What is BREEDPLAN? BREEDPLAN is a modern genetic evaluation system for beef cattle. It offers the potential to accelerate genetic progress, tighten up breeding operations, improve productivity and increase prices for cattle sold for breeding and slaughter Bahame.B.David (2013) Lecture Notes 27th April 2013

BREEDPLAN uses Best Linear Unbiased Prediction (BLUP) technology to produce Estimated Breeding Values (EBVs) for recorded cattle for a range of traits (eg. weight gain, fertility). What is an EBV? An animal’s breeding value is its genetic merit, half of which will be passed on to its progeny. It is difficult to know exact breeding value, for performance traits but it is possible to make good estimates. An Estimated Breeding Value (EBV) is the prediction of the genetic merit of an animal for a particular trait Bahame.B.David (2013) Lecture Notes 27th April 2013

• the animal’s own performance
BREEDPLAN EBVs are calculated from the records of individual herds stored on the database. This includes:- • the animal’s own performance • the performance of all known relatives in the herd • the relationship between performance of different traits • the performance of all animals in the herd over all years of recording Bahame.B.David (2013) Lecture Notes 27th April 2013

Which EBV Traits are computed now?
The BREEDPLAN system currently provides EBVs for up to nineteen traits. These are available in the general areas of:- • calving ease • growth • fertility • carcass • other, such as docility. Bahame.B.David (2013) Lecture Notes 27th April 2013

What are Within-herd EBVs?
The genetic base is calculated separately for each herd based on its first 1000 performance records. The performance of related cattle outside the individual herd is ignored. Within-herd EBVs are obviously not comparable across herds. What are GROUP EBVs? BREEDPLAN is able to separate out genetic from environmental influences. The performance records of different herds are linked through the use of AI sires and their performance recorded progeny across herds. Sale of bulls and cows from one herd to another builds further genetic links. Bahame.B.David (2013) Lecture Notes 27th April 2013

What is a genetic trend? Since the data is analyzed over a number of years, it is possible to calculate the genetic trend for each trait. This trend can be calculated for an individual herd or the breed as a whole. As a breeder you will be able to see if you are making progress in the traits you’re selecting for, and the correlated effect on other economically important traits Bahame.B.David (2013) Lecture Notes 27th April 2013

• Tag/tattoo your calves • Record sire and dam of each calf
What do I need to record? Recording pedigree and performance data for genetic evaluation is relatively simple. The minimum requirements are: • Record birth dates • Tag/tattoo your calves • Record sire and dam of each calf • Weigh calves at least once Record the following Bahame.B.David (2013) Lecture Notes 27th April 2013

• Yearling and 18 month old weights • Mature weights of dams
• Birth weight • Yearling and 18 month old weights • Mature weights of dams • Live animal fat (including intramuscular fat) and muscle scans • Scrotal circumferences • Date bull introduced • Calving difficulty scores Bahame.B.David (2013) Lecture Notes 27th April 2013

Recording helps breeders to 1. Make better breeding decisions
2. Market pedigree stock more effectively 3. Make more money from pedigree beef production Performance recording gives breeders and bull buyers an objective way of assessing the genetic merit of breeding animals. Most accurate way of assessing breeding potential of animal. Bahame.B.David (2013) Lecture Notes 27th April 2013

performance Recording Adds Value To commercial producer
✔ High Weight EBVs – Increased slaughter/sale weights and reduced days to slaughter/sale ✔ Superior Carcase EBVs – Improved carcase conformation ✔ Superior Maternal EBVs – Breeding productive cows that produce more calves during their working lifetime Bahame.B.David (2013) Lecture Notes 27th April 2013

✔ premiums are paid for recorded bulls with superior EBVs
✔ Easy Calving EBVs – Reducing costs associated with difficult calvings including the additional management time, cow/calf deaths, failure to get cows back in calf etc To Pedigree Herds Due to increased returns from high genetic merit animals, buyers seek them out: ✔ Clearance rates for recorded bulls are higher than bulls that are unrecorded ✔ premiums are paid for recorded bulls with superior EBVs Bahame.B.David (2013) Lecture Notes 27th April 2013

A number of factors that will influence the growth of a calf but
The inherited genetic potential is the only part of performance that an animal can pass on to its progeny and it is expressed as an Estimated Breeding Value or EBV for each trait we measure. Bahame.B.David (2013) Lecture Notes 27th April 2013

Basics of Animal Breeding and Genetics improvement

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Basics of Animal Breeding and Genetics improvement

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