Animal Breeding PDF

Phenotype: The physical appearance of an animal. Genotype: The genetic makeup of an animal. Environment: Any non-genetic factor that can influence an animal's phenotype. Examples include: age of dam, sex of offspring, season of birth, and the number of offspring. [1, 2] Breeding V...

Phenotype: The physical appearance of an animal. Genotype: The genetic makeup of an animal. Environment: Any non-genetic factor that can influence an animal's phenotype. Examples include: age of dam, sex of offspring, season of birth, and the number of offspring. [1, 2] Breeding Value : The portion of an animal's genotype for a specific trait that can be passed from parent to offspring. Determined by the additive effects of genes affecting the trait. [2, 3] Non-Additive Value : The portion of an animal's genotype determined by the way genes are combined in the new individual. Unique to each individual and is not passed from generation to generation. Selection: Choosing animals that meet the requirements of the production goals to pass particular traits onto their progeny. Basis : Production system and the goals of the producer. Considerations : Environment, species, breed, sex, and both subjectively measured traits (visual assessment) and objectively measured traits (genetic assessment). Expected Progeny Differences (EPDs): An evaluation of the worth of a sire commonly based on the performance of his progeny. [5, 6] Predict differences in the performance of progeny for animals in the same breed. Available for many important traits and expressed in units of measure for the trait. Can be expressed as positive or negative. Calculated and made available through breed associations. Estimated Breeding Values (EBVs): An evaluation of the values assigned to dams that predict differences in the performance of their offspring. [5, 7] While it is not possible to determine an animal's true breeding value, it is possible to estimate it. Predict the animal's genetic merit for a specific trait. Define the superiority or inferiority of the offspring of an animal. An estimate of the breeding value for a particular trait that is obtained from pedigree and performance information. Ratios/Indexes : Based on multiple traits weighted for economic importance, heritability, and genetic associations among traits.  Examples:$Beef value ($B): Facilitates simultaneous multi-trait genetic selection for feedlot and carcass merit. Feedlot value ($F): An index value expressed in dollars per head, is the expected average difference in future progeny performance for postweaning merit. TSI - Terminal Sire Index : A bio-economic index that ranks individuals for use in a terminal crossbreeding program in swine. Heritability: How much of a trait can be passed to offspring. Degree of Variation : The variation in a phenotypic trait that is due to genetic variation between individuals. Resemblance : Strong resemblance = high heritability, poor/weak resemblance = low heritability. Breeding Systems: Purebred/Straightbred : Mating of animals of the same breed and/or registered in the same breed. Examples: Brahman x Brahman, Hampshire x Hampshire, Yorkshire x Yorkshire Commercial herds can be straightbred but not registered. Results in consistency in genetic frequency (increased homozygosity of traits) and depressed heterosis. Crossbreeding : Mating of animals of different breeds. Produces F1 animals. Takes advantage of positive traits from each breed. Increases the level of heterozygosity and heterosis. Improves performance for economically important traits. Composite Breed : Create a hybrid cross and inter-mate them. Maintain consistency of heterosis in progeny. The goal was not to make a new breed but was an end result. Genetic makeup/breed percentages become stable. Example: Santa Gertrudis. Inbreeding/Line Breeding : Inbreeding is the mating of animals that are related. The level of inbreeding is determined by how related the animals are. Line breeding is the intentional mating of related animals to each other.  Can improve the consistency of important traits but can also cause problems. Mating Systems:Continuous : Females are retained back into the herd. Terminal : All progeny are sold, and replacement females are brought in from outside sources. A combination of these two is common. Terminal Sire Systems: A terminal sire is used when the primary goal is to produce market animals. Static Terminal : Females are purchased from outside or from another herd. Provides the highest level of heterosis. Examples: 2-breed static (purebred Angus x purebred Hereford), 3-breed static (F1 mated to a 3rd purebred breed). Rotational Terminal : Produces replacements and terminal animals. Heterosis/Hybrid Vigor : Definition : The level of superiority of crossbred progeny compared to the average performance of the parental breeds. Result of : Increased heterozygosity and a higher non-additive genetic value due to the masking of recessive genes. Maternal Heterosis : The increase in the production of a cow above that of the average of her parent breeds. Includes maternal ability, reproduction, longevity, calf survivability, pounds of calf weaned, and younger age at puberty. Highest in crossbred females. Maximizes heterosis for maternal traits. Mate back to terminal sires to maximize production. Brahman heterosis (Brahman females x Bos Taurus bulls) results in increased maternal and calf performance.