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Factors Influencing Individual Bull Performance in Central Test Stations¹

The Pennsylvania State University, University Park 16802

Abstract

Records on 8,636 Angus (A), Charolais (C), Hereford (H) and Simmental (S) bulls were used to determine the influence of several genetic and environmental factors on performance traits of bulls in central test stations. Traits recorded were 205-d weight (205W), starting test age (STA) and weight (STW), final test weight (FTW), 365-d weight (365W), 140-d test average daily gain (ADG), lifetime weight/day of age (WPDA), live-estimated M. longissimus area (LA) and fat thickness (FT). Station: breed variances were heterogeneous (P<.01) for A and H (all traits), C (WPDA and FT) and S (205W, LA and FT). Some breed:station heterogeneity was detected (P<.05) for all traits. Within-breed weighted regressions of station variance on mean were significant for A (205W and LA), H (STW, FTW and 365W) and C (205W and FT). Effects of breed:year, station: year and breed x station:year interaction were observed (P<.01) for all traits. The STA and STW were included as nested continuous independent variables; negative partial linear regression coefficients (P<.01) were obtained for 205W, 365W, WPDA and FT on STA, whereas regression coefficients on STW were positive (P<.01) for all traits, indicating the STW and STA adjustments should be applied to postweaning data. Generally, A and H were similar in test performance for 205W, ADG, WPDA, LA and FT. When averaged over all years, A were 9.7 kg heavier than H at the start of the test and in most years had higher (P<.01) FTW. Except for STW and LA, C and S were similar in test performance. When averaged over all years, C were 19.7 kg heavier than S at the start of the test. In most years, C had greater means for estimated LA than did S (85.4 vs 81.2 cm², respectively, averaged over all years). The significant breed x station interaction suggests that means of breeds within stations should be considered when making bull selection decisions within and among stations.

¹ Contribution from the Dept. of Dairy and Anim. Sci., approved by the Director, PAES, as Paper No. 6252 in the Journal Ser.

² Present address: IMC, Terre Haute, IN.