Simulation of genetic control of reproduction in beef cows

Abstract

A stochastic computer model was constructed to simulate cow reproductive performance. Parameters for single-service conception rate and days from calving to first service (postpartum interval) were developed from the literature. Estimates of the heritability and repeatability (h², t) of each of these traits in four simulated data sets were RUN1 (.20, .20), RUN2 (.15, .20), RUN3 (.10, .10), RUN4 (.05, .10). Binomial conception rate parameters were normalized to simulate assumed normal underlying genetic and environmental distributions. Postpartum interval has a non-normal phenotypic distribution that was produced by combining an assumed normal genetic distribution with a Pearson III gamma distribution of environmental effects. The breeding season was 63 d. Simulation outputs included annual conception rate (BCR), first service conception rate (FSCR), date of first service (FS), number of services (NS), conception-calving date (CD), postpartum interval (PPI), actual weaning weight (ACTWW) and adjusted 205-d weaning weight (ADJWW). Realized heritabilities and repeatabilities for these outputs were estimated from half-sib intraclass correlations based on 5 yr of records on 100 herds of 50 cows each. Realized heritabilities (RUN1-RUN4) for BCR, FSCR, FS, NS, CD, PPI, ACTWW and ADJWW ranged from .165-.028, .187-.055, .023-.010, .227-.071, .071-.032, .158-.022, .148-.176 and .156-.203, respectively. Repeatability estimates (RUN1- RUN4) for BCR, FSCR, FS, NS, CD, PPI, ACTWW and ADJWW ranged from .178-.059, .212-.108, .125-.101, .244-.118, .187-.155, .207-.116, .266-.263 and .280-.286, respectively.