Livestock production occupies an important place in agriculture economy of India both through contribution of GDP and employment especially in rural and peri-urban areas. It is also contributing highly nutritious protein food at relatively cheaper prices for human population.The main objective of animal breeding is to bring improvement in livestock using different traits of economic importance. Majority of the economic traits are controlled by multiple genes mostly additively and thus are quantitative in nature rather than being quantitative. The basic principles of inheritance and breeding are the same for all animals; however, implementation of breeding schemes differs considerably from species to species. Reasons for this include differences in reproductive capacity, potential to record traits of interest and available resources for research and implementation. Hence, this book attempts to describe applied breeding methods for different domestic animal species as currently implemented. However, an attempt has been made to include international perspectives wherever relevant because students are expected to deal with international challenges in their future careers. As far as possible, the chapters have been structured the same way for easy across-species comparisons.
Preface Livestock production occupies an important place in agriculture economy of India both through contribution of GDP and employment especially in rural and peri-urban areas. It is also contributing highly nutritious protein food at relatively cheaper prices for human population. The main objective of animal breeding is to bring improvement in livestock using different traits of economic importance. Majority of the economic traits are controlled by multiple genes mostly additively and thus are quantitative in nature rather than being quantitative. The basic principles of inheritance and breeding are the same for all animals; however, implementation of breeding schemes differs considerably from species to species. Reasons for this include differences in reproductive capacity, potential to record traits of interest and available resources for research and implementation. Hence, this book attempts to describe applied breeding methods for different domestic animal species as currently implemented. However, an attempt has been made to include international perspectives wherever relevant because students are expected to deal with international challenges in their future careers. As far as possible, the chapters have been structured the same way for easy across-species comparisons. In this book, brief history of population genetics, domestication of livestock species, classification of breeds, economic characteristics of different livestock species & poultry and their importance, basic statistics, qualitative and quantitative inheritance, gene and genotype frequency and factors influencing gene frequency, values and means of population, methods of estimation and uses of heritability and repeatability, correlations, selection, response to selection, basis of selection, progeny testing, open nucleus breeding system, sire evaluation, methods of selection, breeding or mating systems, heterosis or hybrid vigor definitions and current livestock and poultry breeding programmes have been discussed in different chapters. The subject matter has been dealt with in a logical sequence so that the reader is conveyed from simple to more complex interpretation with relative ease. It is felt that the reader which are likely to comprise mostly of graduate and post graduate student of animal breeding and researcher will be able to get a deeper insight and better perceptions into the realm of the dynamic science of animal breeding.
Introduction From the very early days human beings depend on animals and animal products for food and other requirements. In dairy and poultry farms high yielding animals are reared. These high yielding animals are produced by hybridization experiments. Previously the animals were developed basing on unscientific methods. Before the discovery of principles of heredity human beings have selected the animals with required characters and learned to develop the plants having the selected characters. This phenomenon is called Artificial selection. However, an increased knowledge of biology, especially genetics, has helped in improving the quality of animals and animal products as per the human requirements.
Domestication of Livestock Domestication (from Latin domesticus) is the process whereby a population of animals or plants is changed at the genetic level through a process of selection, in order to accentuate traits that benefit humans. It differs from taming in that a change in the phenotypical expression and genotype of the animal occurs, whereas taming is simply the process by which animals become accustomed to human presence. In the Convention on Biological Diversity, a domesticated species is defined as a “species in which the evolutionary process has been influenced by humans to meet their needs.” Therefore, a defining characteristic of domestication is artificial selection by humans. Humans have brought these populations under their control and care for a wide range of reasons: to produce food or valuable commodities (such as wool, cotton, or silk), for types of work (such as transportation, protection, and warfare), scientific research, or simply to enjoy as companions or ornaments. Plants domesticated primarily for aesthetic enjoyment in and around the home are usually called house plants or ornamentals, while those domesticated for large-scale food production are generally called crops. A distinction can be made between those domesticated plants that have been deliberately altered or selected for special desirable characteristics and those plants that are used for human benefit, but are essentially no different from the wild populations of the species. Animals domesticated for home companionship are usually called pets while those domesticated for food or work are called livestock or farm animals.
Definition of Breed A breed is a group of animal’s related similar characters like general appearance, size, features and configuration etc. A group of individual which have certain common characteristicsthat distinguish them from other groups of individuals is known as Species.
There are certain inherited traits (characters) in various species of livestock which are economically important. These traits have to be improved for increased production like milk, meat, egg, wool, etc.
Introduction Statistics is a field of mathematics that pertains to data analysis. Statistical methods and equations can be applied to a data set in order to analyze and interpret results, explain variations in the data, or predict future data. A few examples of statistical information we can calculate are: Average value (mean)
Quantitative Versus Qualitative Inheritance There is a continuum of traits being inherited as a Mendelian trait with simple inheritance and traits having quantitative inheritance without well separated classes and with many genes involved. Classification of traits in relation to mode of inheritance and environmental tolerance are shown in Figure 1.2. First there are the well known traits with simple Mendelian mode of inheritance. The trait with quantitative genetic inheritance is caused by segregation of many gene pairs, each with small effect. At the same time the trait is influenced by a lot of minor environmental effects. Diseases will often be ‘either/or traits’ as the simple Mendelian traits. Cases in which the severity of the disease has a normal distribution can also be found. In many production diseases the disease only occurs when a genetically prone individual is exposed to adverse environmental effects. Figure 1. Classification of traits in relation to mode of inheritance and environmental tolerance.
Gene Frequency A population, in the genetic sense, is not just a group of individuals, but a breeding group and the genetics of a population is concerned not only with the genetic constitution of the individuals but also with the transmission of the genes from one generation to the next. In the transmission the genotypes of the parents are broken-down and a newest of genotypes is constituted in the progeny, from the genes transmitted in the gametes. The genes carried by the population thus have continuity from generation to generation, but the genotypes in which they appear do not. The genetic constitution of a population, referring to the genes it carries, is described by the array of gene frequencies, that is, by specification of the alleles present at every locus and the numbers of proportions of the different alleles at each locus. If for example, A1 is an allele at the A locus, then the frequency of A1, is the proportion or percentage of all genes at this locus that are the A1 allele. The frequencies of all the allele at any one locus must add up to unity, or 100 percent.
The amount of variation is measured and expressed as the variance. When values are expressed as deviations from the population mean the variance is simple the mean of the squared values. For example, the genotypic variance is the variance of genotypic values and the environmental variance is the variance of environmental deviations. The total variance is the phenotypic variance of the variance of phenotypic values, and is the sum of the separate components.
The concept of value, expressible in the metric units by which the character is measured. The value observed when the character is measured on an individual is the phenotypic value of that individual. All observations of means, variance, or covariances, must clearly be based on measurements of phenotypic values. In order to analyse the genetic properties of the population we have to divide the phenotypic value into two componants. The first division of phenotypic value is into components attributable to the influence of genotypic and environment. The genotype is the particular assemblage of genes possessed by the individual, and the environment is all the non-genetic circumstances under the term ‘environment’ means that the genotype and the environment are by definition the only determinants of phenotypic value. The two components of value associated with genotypic value and the environmental deviation.
Estimates of heritability use statistical analyses to help to identify the causes of differences between individuals. Because heritability is concerned with variance, it is necessarily an account of the differences between individuals in a population. Heritability can be univariate–examining a single trait – or multivariate – examining the genetic and environmental associations between multiple traits at once. This allows a test of the genetic overlap between different phenotypes: for instance hair colour and eye colour. Environment and genetics may also interact, and heritability analyses can test for and examine these interactions (GxE models).
In genetic studies it is necessary to distinguish two causes of correlation; is chiefly pleiotropy, though linkage is a cause of transient correlation, particularly in populations derived from crosses between divergent strains. Pleiotropy is simply the property of a gene whereby it affects two or more characters, so that if the gene is segregating it causes simultaneous variation in the characters as affects. For example, genes that increase growth rate increase both stature and weight, so that they tend to cause correlation between these two characters. The degree of correlation arising from pleiotropy expresses the extent to which two characters are influenced by the same genes. But the correlation resulting from pleiotropy is the overall, or net, effect of all the segregating genes that affect both characters. Some genes may increase both characters, while others increase one and reduce the other the former tend to cause a positive correlation the latter a negative one. So pleiotropy does not necessarily cause a detectable correlation. The correlation resulting from environmental causes is the overall effect of all the environmental factors that vary; some may tend to cause a positive correlation, others a negative one.
Selection is an important tool for changing gene frequencies to better fit individuals for a particular purpose. It may be defined as a process in which certain individuals in a population are preferred to others for the production of the next generation. Selection is of two kinds
The response to selection is the change produced in the population mean through selection. This is achieved through selecting as parents of the next generation, individuals with highest genetic merit and whose progeny will, as a group, have the highest possible genetic merit for the trait in question.
Individuality tells us what an animal seems to be; his pedigree tells us what he ought to be, but the performance of his progeny tells us what he is Effectiveness of selection depends on ability to recognize those animals, which possess superior inheritance. Those superior animals must be mated together for the production of offspring. The aids available to estimate the breeding value of an animal is through the phenotype of an animal or its relatives.
An animal breeder usually interested in various economic traits and when wishes to improve them in the herd/flock, he has three general methods at his disposal. Tandom method, independent culling level method and index selection method. Tandom Method It involves selection for one trait at a time and until it reaches at a satisfactory level, and then for a third trait etc. This method is applicable only when the different traits in question are entirely independent or positively genetically associated to each other. Its effectiveness decreases with the increase in number of traits. This method is least desirable of all the methods.
Open nucleus breeding system is considered to be a best approach to bring genetic improvement in livestock. This system was first introduced New Zealand for faster genetic improvement of sheep. The milk recording under field condition is quite expensive. Moreover, farmers are not under any obligation to retain the animal till the lactation is completed. The generation interval is also very large as it takes about 6-7 year by the time complete record on progeny testing programmes in developing countries is available, so that the effective genetic improvement is small. Use of best proven bull on the elite cow, which are best 5-10% of the cow for genetic improvement of the population. The net genetic gain in the herd considering the actual genetic improvement from various parents off spring path is around 0.7% per annum. Considering these situation in develop countries it has been proposed that ‘nucleus’ herd be created where males from the best cows are obtained. The nucleus herd would be open in the sense that the lowest yielding cows are culled every year and are replaced by procurement of that many high yielding cow from farmers herd. The nucleus herds are utilized entirely for production of males for breeding purposes in the population.
Progeny testing in India was introduced in the late 1950’s the first sire index in our country was suggested by Krishnan (1956) which was, however, similar to the herdmate and contemporary comparison methods. Robertson and Rendel (1954) stated that an efficient method of sire evaluation should satisfy two conditions:
The aim of mating systems are either to increase or decrease the homozygosity of the progeny compared with the parents or in some cases, to maintain the degree of homozygosity unchanged. This aim constitutes the basis of the following classification of mating systems:
Heterosis, hybrid vigor, or outbreeding enhancement, is the improved or increased function of any biological quality in a hybrid offspring. The adjective derived from heterosis is heterotic.Heterosis is the occurrence of a superior offspring from mixing the genetic contributions of its parents. These effects can be due to Mendelian or non-Mendelian inheritance.
General Selection Procedures for Dairy Breeds Selection of Dairy Cows Selecting a calf in calf show, a cow in cattle show by judging is an art. A dairy farmer should build up his own herd by breeding his own herd. Following guidelines will beuseful for selection of a diary cow. Whenever an animal is purchased from cattle fair, it should be selected based upon its breed characters and milk producing. History sheet or pedigree sheet which are generally maintained in organized farmsreveals the complete history of animal.The maximum yield by dairy cows are noticed during the first five lactations. So generally selection should be carried out during First or Second lactation and thattoo are month after calving.?Three successive complete milkings has to be done and an average of it will givea fair idea regarding production by a particular animal. A cow should allow anybody to milk, and should be docile.?It is better to purchase the animals during the months of October and November.?Maximum yield is noticed till 90 days after calving.
Cattle Breeding Policies and Programmes in the Planning Process It is necessary to see how the issues relating to Cattle Breeding have been dealt with in the successive Plan periods starting from the First Five Year Plan. It is seen that, while the issue of surplus cattle has been handled in different ways in the various Plan documents, some discussing this issue at great length and other remaining completely silent on the subject, other issues such as cattle development, genetic improvement and breeding etc., have also received varying degrees of emphasis in the different Plans.
Introduction India has vast animal genetic resources with a wide variety of indigenous farm animals including cattle. The cattle breeds have evolved over generations to adapt to the agro-climatic and socio-economic needs of the people. Domestic animal diversity is defined as the spectrum of genetic differences within each breed and across all breeds within each domestic animal species, together with the species differences; all of which are available for the sustainable intensification of food and agriculture production. The domestic animal diversity has evolved over millions of years through the processes of natural selection forming and stabilizing each of the species used in food and agriculture. Over the more recent millennia the interaction between environmental and human selection has led to the development of genetically distinct breeds. Selection processes, directed by both humans and the environment, together with the random sampling processes causing genetic populations to drift over generations, have accelerated the development of the diversity within species leading to the creation of distinct genetic differences amongst breeds.
References Berge, S., 1961. The historical development of animal breeding. In: Scientific problems of recording systems and breeding plans of domestic animals (E. Schilling, ed). 11, 109-127. Max-Planck. Inst. Tierz. Tierernährung, Mariensee/Trenthorst. De Vries, A. G., 1989. A method to incorporate competitive position in the breeding goal. Anim. Prod. 48:221-227. Falconer, D. S., 1960. Introduction to Quantitative Genetics. Oliver and Boyd, London. Falconer, D. S., and T. F. C. Mackay, 1996. Introduction to Quantitative Genetics. Longman, Harlow (3rd edition). Hazel, L. N., 1943. The genetic basis for constructing selection indexes. Genetics 28:476- 490. Hazel, L. N., and J. L. Lush, 1942. Efficiency of three methods of selection. J. Hered. 33:393-399. Henderson, C. R., 1952. Specific and general combining ability. In: Heterosis (J.W. Gowen, ed). pp. 352-370. Iowa State College Press, Ames, Iowa. Henderson, C. R. 1950. Estimation of genetic parameters. Ann. Math. Statist. 21:309. Henderson, C. R., H. W. Carter and J. T. Godfrey, 1954. Use of contemporary herd average in appraising progeny tests of dairy bulls. J. Anim. Sci. 13:949. Hopkins, I.R., 1978. Some optimum age structures and selection methods in open nucleusbreeding schemes with overlapping generations. Anim. Prod. 26: 267-276. Hopkins, I.R. and James, J.W., 1978. Theory of nucleolus breeding Schemes into overlappinggeneration. Theoretical and applied genetics, 53:17-24. James, J.W., 1977. Open nucleus breeding systems. Animal Production. 24: 287-305. James, J.W. 1978. Effective population size in open nucleus breeding scheme. Acta Agric. Scand. 28:387-392. Jasiorowski H.A., 1990. Open nucleus breeding schemes - new challenge for the developing countries. In: Zurkowski M. (ed), Proceedings of a Conference on Open Nucleus BreedingSystems, Biatobrzegi, Poland, 1-19 January 1989. FAO (Food and Agriculture Organization of the United Nations), Rome, Italy. pp. 7-12. Kasonta, J.S. and Nitter, G., 1990. Efficiency of nucleus breeding scheme in dual purposecattle in Tanzania. Animal Production 50: 295-251. Keller D.S., Gearheart W.W. and Smith C., 1990. A comparison of factors reducing selection response in closed nucleus breeding schemes. Journal of Animal Science 68:1553-1561. Lush, J. L., 1945. Animal Breeding Plans. Iowa State College Press, Ames, Iowa.- 34 - Lush, J. L., 1994. The Genetics of Populations. Prepared for publication by A. B. Chapman, R. R. Shrode and withan addendum by J.F. Crow. College of Agriculture, Iowa State University, Ames, Iowa. Special Report 94.
