Abstract
The Texas A&M Beef Cattle Production model was expanded to include basic concepts of quantitative genetics. The traits simulated were birth weight, yearling weight, mature weight and milk production. In the original model genetic potentials were specified by growth rate, mature weight and milk production. The progeny inherited these traits from the dam with no contribution from the sire. The model was modified so that the progeny inherited attributes from both the sire and the dam. The incorporation of genetics into the model allowed for the introduction of variation among individuals and from generation to generation. This was achieved by interfacing the original model with stochastic genetic subroutines. The variation introduced in the simulated populations was used to examine different selection scenarios. Application of restricted selection index for desired genetic change, developed by Yamada et al. (1975), was examined. The index included birth weight and yearling weight. Correlated gains in mature weight and milk production were also studied. This allowed for comparison of different selection objectives in different genotypes. Five within herd selection experiments were carried out to illustrate the model. Selection index methods using birth weight and yearling weight resulted in more gain in all traits compared to single trait selection on yearling weight. During selection for birth weight and yearling weight dystocia patterns were also examined. Dystocia patterns in the small moderate-sized breed were similar to those in the large breed when mature size was increased. In the small to moderate-sized breed selection on yearling weight alone resulted in the low dystocia levels while selection for reduced birth weight in the large breed actually reduced dystocia levels. Analysis of selection response for birth weight and yearling weight over twenty years of simulation using simple linear regression yielded results that were in general agreement with expected gains computed a priori.
Dzama, Kennedy (1993). Genetic simulation of beef cattle production for growth and milk production. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -1525886.