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Herd Differences and Genetic Trends in Iowa Pigs¹

Iowa State University, Ames

Abstract

Data from an experimental herd, maintained by boars purchased from breeders involved in the Iowa swine testing program, were used to assess the importance of genetic herd differences and to estimate genetic trends in the breeds. Genetic herd differences were found to account for a very small portion of the total variance in gain and fatness. Estimates of genetic trends (from regressions of adjusted progeny performance on age of dam within periods) were much smaller than the trends in performance at the testing stations and even different in sign.

A questionnaire was sent to breeders to assess what criteria they used in their choice of breeding stock. There was considerable exchange of stock among herds and also among states. Type and appearance were the most important items in selecting boars, while performance test records had a lower priority. The dilemma, having large phenotypic changes in performance contrasted with low estimates of genetic change and little evidence of selection, needs to be resolved.

¹ Journal Paper No. J–5782 of the Iowa Agricultural and Home Economics Experiment Station, Ames. Project No. 1424. This work has received assistance from Contract AT(11–1)–7O7 with the U.S. Atomic Energy Commission.