Animal Scince 1011 Heritability exam 2

Heritability

The proportion of phenotypic variation in a population that is due to the genetic variation in a population.

Heritability values range

0 - 0.2 = lowly heritable (reproductive traits: fertility, litter size); 0.2 - 0.4 = moderately heritable (growth traits: birth, weaning, yearling weights); 0.4 - 0.6 = highly heritable traits (carcass traits: HCW, REA, WBSF, marbling).

Phenotype

Phenotype = Genotype + Environment.

Performance as an indicator

Performance is only a good indicator of genetic merit if heritability for that trait is moderate - high.

Breeding Schematic

Heritability and Performance can tell a lot about an individual's worth as a genetic parent for that trait.

Complex computer programs

Analyze performance data of individuals, their relatives, and their offspring and create a genetic prediction.

Estimated breeding values (EBVs)

Values that represent the genetic potential of an individual based on performance data.

Expected progeny differences (EPDs)

Predictions of the genetic merit of an animal's offspring.

Estimated transmitting abilities (ETAs)

Values that indicate how much better or worse an individual is than average.

Performance Records

Extensive record-keeping, typically done in seedstock operations, including birth weight, weaning weight, yearling weight, average daily gain, calving ease, back fat thickness, ribeye area, hot carcass weight.

Seedstock producers

Submit records to breed associations that can tabulate genetic predictions.

Commercial producers

Use performance records to make purchase (animal or gametes) and mating decisions to improve herd performance.

Calves sired by Bull A

6.6 - -5.9 = 12.5 lbs. Calves sired by Bull A will be 12.5 lbs. heavier at birth than calves sired by Bull D.

Calves sired by Bull A (yearling weight)

39.5 - -14.4 = 53.9 lbs. Calves sired by Bull A will be 53.9 lbs. heavier at one year than calves sired by Bull D.

Mating plans

Can be based on randomness, performance/visual appearance (phenotype), genetic relationship (pedigree).

Random mating plan

Selecting which animals are going to be bred without selecting the breeding pairs.

Females in random mating

Can be given random numbers (1 - 100).

Gate-cutting

The first 25 females to enter a pasture.

Chute-cutting

The first 25 that go through the chute.

Performance based mating plans

Mating strategies based on the performance of animals.

Positive assortative mating

Breeding animals of the same type of quality.

Negative assortative mating

Breeding animals of opposite (dissimilar quality) to each other.

Corrective mating

Breeding my worst females to my best males and vice versa.

Pedigree-Based Mating Plans

Mating plans based on the lineage and genetic history of animals.

Inbreeding

Mating closely related animals, increasing homozygosity.

Inbreeding depression

A decrease in performance of inbreds.

Use of Inbreeding

Almost exclusively used in seedstock operations due to the need for thorough record-keeping.

Outbreeding/Outcrossing

The mating of less-related individuals to increase genetic diversity.

Crossbreeding

Mating individuals from separate breeds, popular for breed complementarity and heterosis.

Breed complementarity

Mating different breeds with complementary breeding values to improve overall performance.

Heterosis (Hybrid Vigor)

Superior performance of outbred individuals relative to the average performance of the parent populations.

Compare/contrast Positive and negative assortative matings

Positive assortative mating involves breeding similar quality animals, while negative involves breeding dissimilar quality animals.

Compare/contrast Inbreeding/outcrossing/crossbreeding

Inbreeding involves closely related individuals, outcrossing involves less-related individuals, and crossbreeding involves different breeds.

Compare/contrast Breed complementarity/hybrid vigor

Breed complementarity focuses on complementary strengths, while hybrid vigor emphasizes superior performance of outbred individuals.

Situations for inbreeding/outcrossing/crossbreeding

Producers may choose these methods based on desired traits and genetic diversity.

Culling decisions

Using performance and heritability to determine which animals to remove from breeding.