Animal genetics, breeding and reproduction.pptx

Animal Genetics

1. Animal genetics, breeding and reproduction By the end of this unit you should be able to: ✔ explain different breeding systems in animal production ✔ explain the advantages of cross-breeding ✔ explain genetic engineering in livestock production ✔ differentiate between the terms: (a) ovulation; (b) fertilisation ; (c) gestation; (d) oestrous cycle; (e) kindling, parturition, farrowing ✔ describe the process of artificial insemination (AI) in farm animals ✔ evaluate the use of AI in farm animals ✔ state the benefits of oestrus synchronisation ✔ relate the structure of the parts of an egg to its function ✔ describe the process of incubation in poultry.

2. Breeding systems in animal production Breed A breed is a group of animals of the same species that have certain characteristics in common . These characteristics are usually: Physical-such as coat colour or shape of the body. B ehavioural -such as docility.

3. B reeding system A breeding system involves the mating of a male animal with a female animal. Both animals are chosen for their desirable characteristics. When breeders want to produce more suitable animals, they must decide which characteristics are important.

4. Variation among individual animals of a particular breed is influenced by their genotype and the environment . For example, dairy cows are bred for their high milk yields, but if the cows are put on poor pasture their yields will not be as high as those cows fed on a better diet. Genotype- genetic make up of an animal

5. H eritability H eritability -the effect of genes on a characteristic. Many important characteristics, such as milk yield, carcass quality and rate of growth, are controlled by more than one pair of genes. Heritability- traits that are inherited.

6. C ontinuous variation C haracteristics which change gradually . Examples: W eight H eight

7. calculate the heritability Example Milk yield, by keeping records of the volume of milk produced by each cow and then determining the average for each individual and the average for the herd. Cows that have averages above the herd average would be the ones to use for breeding if the farmer wants an increased yield.

8. Cross-breeding Cross-breeding occurs when an animal is mated with another animal of the same species but of a different breed . Example Hereford cattle may be mated with Aberdeen Angus cattle to give offspring with an increased growth rate. Animals that are cross-bred often show increased vigour and productivity.

9. H ybrids The genes from the two breeds are combined. Characteristics controlled by the dominant genes from both breeds tend to be expressed. The offspring of cross-breeding are called hybrids.

10. Inbreeding Inbreeding occurs when animals of the same breed are mated with one another. These animals will be closely related and genetically similar to one another. Animal breeders use inbreeding to produce superior offspring ( in the short term) and to maintain desirable characteristics within the breed .

11. Risks of inbreeding If inbreeding is used for many generations, there is actually a decrease in desirable characteristics and an increase in undesirable characteristics. This is known as inbreeding depression. decreased resistance to infection S maller in size physical defects S horter lifespan.

12. Upgrading Upgrading involves crossing native, or local, breeds with breeds from other countries or regions of the world. Cross-breeding animals in a temperate climate with an animal in a tropical climate. Example Their food sources may differ T hey cannot tolerate the heat . L ess resistance to the pests and diseases. For these reasons, cross-breeding of local breeds with high-producing imported breeds can have advantages. Desirable characteristics of the imported breed can be introduced into a local breed. E xample is the development of the Jamaica Hope dairy cattle and the Jamaica breeds of beef cattle

13. Back-crossing Back-crossing is the term given to the crossing of a hybrid organism with one of its parents. B oth plant and animal breeding programmes. This type of cross is carried out to obtain offspring that are similar to the parent with the desirable characteristic. Back-crossing can maintain desirable characteristics in a breed and does not introduce new genes. D oes not work well for characteristics such as growth rate, nor does it work for recessive genes

14. Advantages of cross-breeding Hybrid vigour (heterosis) combines the genes of the two breeds. The resulting offspring have an increase in heterozygous genes . Hybrid offspring may be more fertile and have a longer lifespan than their parents. The increased fitness of the hybrid generation is called hybrid vigour or heterosis. Shows superior qualities over both parents

15. Dominant and Recessive Genes D esirable characteristics are controlled by dominant genes (Genes that express themselves more strongly), and hybrid vigour results from an increase in heterozygous genes. Undesirable characteristics are often controlled by recessive genes ( a gene that can be masked by a dominant gene) . An increase in heterozygous genes means that these characteristics do not show in the hybrid offspring.

16. Example increase in heterozygosity can benefit a breed can be shown by crossing two breeds of pigs. Breed X sows- produce large litters but the survival rate of the piglets is low. Breed Y sows- have fewer piglets in each litter but the survival rate of the piglets is high. Large litters are controlled by the dominant allele A and percentage survival is controlled by the dominant allele B . If a pure breeding sow from Breed X is crossed with a pure-breeding boar from Breed Y, then the piglets will show hybrid vigour

17.   Gametes- reproductive cell 

18. Disease resistance An inbred resistance to disease in farm animals means that farmers depend less on the use of drugs to treat diseases. There is therefore a decreased risk of these drugs getting into human food. The benefits to farmers are that veterinarian’s bills and production costs are lower. In addition, disease resistance reduces the chances of pathogenic organisms becoming resistant to drugs.

19. Many people think that if animals are kept healthy and reared under good conditions, they are less likely to suffer from diseases. This is true, but resistance to some diseases is also inherited.

20. Improved production Cross-breeding will result in improved production in farm animals if breeds with desirable characteristics are chosen. Cross-breeding results in increased vigour of the offspring. It also improves survival rate and leads to faster growth rates. A farmer or animal breeder will always choose the fittest animals from which to breed, therefore continuing the improvement of the stock.