Experimental selection for calving ease and postnatal growth in seven cattle populations. I. Changes in estimated breeding values

¹ USDA, ARS, U.S. Meat Animal Research Center, Clay Center, Nebraska, 68933-0166

^* To whom correspondence should be addressed. E-mail: gary.bennett{at}ars.usda.gov.

	Abstract

Selection was used to create select and control lines within 4 purebred and 3 composite cattle populations. Both lines were selected for similar direct yearling weight and maternal weaning weight EBV. Select lines were selected for lower 2-yr-old heifer calving difficulty score EBV and control lines for average birth weight EBV. Select (n = 6,926) and control (n = 2,043) line calves were born from 1993 through 1999 and selection began with the 1992 mating. High replacement rates resulted in 2,188 births to select line and 598 births to control line heifers. Data used to calculate EBV came from these populations and 15 yr of data preceding the experiment. Calving difficulty was scored from 1 (no assistance) to 7 (caesarean). Calving difficulty scores from all twins, malpresentations, and cows 3-yr-old and older were eliminated. Except for the first year when single trait BLUP was used, a multiple trait BLUP was used to calculate direct and maternal EBV for calving difficulty score, birth weight, and weaning weight, and direct EBV for postweaning gain. Sires (n = 498) were selected from those born in both the preceding populations and the select and control lines. In purebred populations, some industry sires (n = 88) were introduced based on their EPD. Tests of mean select and control line EBV differences of calves born in the final 2 yr were based on among population variation. Select line direct EBV were 1.06 lower for heifer calving difficulty score (P < 0.001) and 3.5 kg lower (P < 0.001) for birth weight than control. Average differences for other EBV were small and not significant. Yearling weight EBV was intentionally increased in both select and control lines of purebred populations. Angus, Hereford, Charolais, and Gelbvieh yearling weight EBV in control lines increased 32.4, 27.2, 21.0, and 10.5 kg, respectively, from 1991 and 1992 to 1998 and 1999 compared to an average increase of 2.7 kg in composite populations. Birth weight direct EBV in purebred control lines increased by approximately 8% of yearling weight EBV increases. Selection based on multiple trait BLUP was able to create lines differing in calving difficulty score and birth weight EBV, but not in weaning weight and postweaning gain EBV. Differences between lines should be useful for evaluating BLUP and other traits and identifying potential limitations of genetically decreasing calving difficulty score and birth weight.

Key Words: birth weight, calving difficulty, cattle, estimated breeding value, genetic trend, selection

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				G. L. Bennett, R. M. Thallman, W. M. Snelling, and L. A. Kuehn Experimental selection for calving ease and postnatal growth in seven cattle populations. II. Phenotypic differences J Anim Sci, September 1, 2008; 86(9): 2103 - 2114. [Abstract] [Full Text] [PDF]