Terry Stewart

 

Terry Stewart's Main Page

Research Program

Terry S. Stewart     Genetic Trend for MLI

Research Interests

Animal Breeding and Genetics

The goals are the optimization of genetic evaluation systems and the definition of breeding objectives to maximize the rate of improvement of domestic livestock.

The current focus of research is the development and utilization of quantitative genetic technology for national genetic evaluation of swine. The STAGES (Swine Testing and Genetic Evaluation System), used by the U.S. Swine Breed Associations, resulted from this research. Research activity includes variance-covariance estimation using the STAGES database, investigation of additional traits of economic importance that can be measured by on-farm performance programs, and development of across-breed genetic evaluation technology. Collaborative research with faculty in Agricultural Economics determines economic values of individual traits and costs of evaluation procedures. Genetic and economic information is combined to develop breeding objectives and selection criteria that optimize selection procedures to maximize the net value of genetic improvement programs. A 150-sow herd is dedicated to animal breeding research. An extensive database has accumulated from this herd to study genetic control of maternal productivity traits and correlated effects in growth traits.

Current research protocols study the efficacy of selection in purebred populations to improve growth and maternal performance of crossbred offspring. Additionally, data are being collected on the correlation of within- and across-breed genetic evaluations using purebred and crossbred offspring. Mathematical modeling and Expert Systems techniques are used to complement the in vivo research program. Models have been developed to study selection criteria to improve lifetime productivity of beef cattle, the effect of alternative age of weaning on sow productivity in swine, and structure of contemporary group design in genetic testing programs on the accuracy of genetic evaluation.

Collaborative work is being conducted with researchers in Australia on decision support tools as a way of transfering Genetic knowledge to livestock producers.  Deterministic models have been developed to predict genotype environmental interactions for crossbred mating programs in tropical production environments. Software is being tested to couple the biological models with economic, production and marketing information so a livestock producer can utilize the information to make decisions of mating systems and production practices to optimize the breeding program for specific markets.

Research Techniques

  • Quantitative genetic techniques
  • Multivariate mixed model statistical estimation techniques
  • Computer simulation modeling
  • Economic optimization procedures
  • Expert Systems and Decision Support tools

Selected Publications

Stewart, T. S., D. H. Bache, D. L. Harris, M. E. Einstein, D. L. Lofgren, and A. P. Schinckel. 1990. A bioeconomic profit function for swine production: Application to developing optimal multitrait selection index. Journal of Animal Breeding and Genetics 107:340-350.

Marshall, T. E., and T. S. Stewart. 1990. Simulated effects of selection and cow culling on profitability of beef production. Proceedings of World Congress on Genetics Applied to Livestock Production, Edinburgh, Scotland, 15:311-314.

Lofgren, D. L. and T. S. Stewart. 1994. Optimal contemporary group structure to maximize genetic progress through genetic evaluation of swine. Journal of Animal Science 72:2254-2259.

Brubaker, Mark, Donna Lofgren, Mark Einstein, and Terry Stewart. 1994. Comparison of litter adjustment factors in Yorkshire and Landrace data. Journal of Animal Science 72:2538-2543.

Newman, S., T. S. Stewart , M. Goddard, and M. Gregory. 1997. HotCross - A Decision Support Aid For Crossbreeding in the Tropics 12th meeting of Association for Advancement of Animal Breeding and Genetics 12:400-403.

Stewart, T. S.1998. Quantity, Quality and the Consumer: Limitations to Breeding Objectives.  Proceedings of World Congress on Genetics Applied to Livestock Production. 25:327-334.