Ronald M. Lewis
Date of this Version
Zimmermann, M. J. 2018. Identifying breed effects for cow mature weight. M.S. Thesis. University of Nebraska-Lincoln.
Mature weight (MWT) in beef cattle has increased over the past 30 yr. In general, larger cows are costlier to maintain than smaller cows, and their profitability depends on their production environment. A wide range of beef production environments exist in the United States. There are also a variety of beef cattle breeds that can be chosen and mated to create a type of cow which will be optimally suited to excel in a given environment. However, there remains a need for tools allowing effective comparison among breeds to facilitate such decision making. Unfortunately, estimated progeny differences (EPD) for MWT are not currently available in most breeds. However, understanding growth to maturity and estimating breed effects for MWT can facilitate more informed breeding systems that rely on MWT as a proxy for cow maintenance costs.
First, growth from weaning to maturity was studied using weight data of crossbred cows from the Germplasm Evaluation Program (GPE) at the U.S. Meat Animal Research Center in Clay Center, Nebraska. Brody, spline, and quadratic functions were fitted. For the spline and quadratic functions, MWT was estimated at 6 yr of age from fitted parameters. The spline function seemed to fit these data best, but the Brody function was more reliable for estimating MWT. Its estimated values were consistent even when weights taken at younger ages were used to estimate MWT, with few extreme MWT estimates generated.
Second, MWT estimates from the aforementioned functions were analyzed by fitting an animal model including fixed effects of breed fractions and birth year-season contemporary group, and linear covariates of direct and maternal heterosis. Resulting breed covariate solutions were divided by 2 to obtain breed of sire solutions. Breed of sire solutions were adjusted for sire sampling to determine the breed effect for MWT in each of 18 commonly-used beef cattle breeds represented in the GPE population. Since MWT EPD were not available for most breeds, yearling weight EPD was used as a proxy. The breed effects calculated can help seedstock producers identify appropriate breeds that will suit their operation’s unique environments and breeding goals.
Advisor: Ronald M. Lewis