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Mating System by Environment Interactions for Weaning Weight in Hereford Cattle¹

Colorado State University, Fort Collins 80523

Abstract

Weaning weight data collected at the San Juan Basin Research Center, Hesperus, from 1950 through 1971 on 1,234 inbred and 1,646 line-cross Hereford calves representing 10 lines were analyzed. The objective of the study was to assess the importance of heterosis estimates calculated in different levels of environment. Age adjusted weaning weights of both sexes were analyzed separately by least-squares procedures. The model included season of birth (B), good vs poor production years (P), years within production levels (Y/P), age of dam (A), line of sire (L), and mating system (MS) as main effects. All first order interactions involving mating system and each of the other main effects, except Y/P, were included in the model: (B x MS), (P x MS), (A x MS), and (L x MS).

The (B x MS) interaction effects were negligible in both sexes but the (P x MS) interaction approached significance for female weights where linecrosses exceeded inbreds by 10.7% in good years and 8.9% in poor years. The interaction (A x MS) approached significance for female weights. However, in both sexes, the heterosis estimates in the 2-year age of dam group tended to be:th,e largest. Slower development and less milik. production of younger inbred dams as compared to linecross dams may account for this phenomenon. The (L x MS) interaction was highly significant in both sexes where heterosis estimates ranged from 1.1 to 24.5% for heifer weights and from 5.3 to 22.1% for bull weights. There appeared to be an inverse relationship between the performance of a line as inbreds and the performance of linecrosses from the same line of sire.

Heterosis estimates calculated by comparing differences between inbred and linecross Hereford calves produced from the same line of inbred sire tended to show some variability within level of environment and sex of calf.

¹ Approved for publication as Scientific Paper 2210 of the Colorado Experiment Station.

² Present address: Agriculture Canada Research Station, Lethbridge, Alberta, Can. T1J 4B1.