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Unformatted text preview: D. G. Riley, C. C. Chase, Jr., S. W. Coleman, T. A. Olson and R. D. Randel and size at first conception and characteristics of their first calves Evaluation of tropically adapted straightbred and crossbred beef cattle: Heifer age doi: 10.2527/jas.2009-2573 originally published online June 25, 2010 2010, 88:3173-3182. J ANIM SCI http://jas.fass.org/content/88/10/3173 the World Wide Web at: The online version of this article, along with updated information and services, is located on www.asas.org by guest on October 10, 2011 jas.fass.org Downloaded from ABSTRACT: The objectives of this work were to es- timate genetic effects for age and size at estimated time of first conception, and temperament in straightbred and crossbred heifers (n = 554) produced from Romo- sinuano, Brahman, and Angus cattle, and to evaluate first-parturition performance of heifers, including calf birth weight, occurrence of calving difficulty, occurrence of poor vigor in their newborn calves, and calf mortal- ity. At approximately 7 mo of age, weaned heifers were pastured with Mashona or Tuli bulls until confirmed pregnant. Body weight, hip height, exit velocity (m/s), and chute temperament score (1 = calm, no movement; 5 = continuous movement, struggling) were recorded at 28-d intervals until heifers averaged 19 mo of age. Age at first conception was estimated as age at calving minus 285 d. Regression analyses were used to estimate BW and hip height at age of first conception. Brahman heifers were older, heavier, and had greater hip height than other straightbred groups ( P < 0.05) and most crossbred groups. Brahman and reciprocal Brahman- Angus heifers had greater ( P < 0.05) exit velocity than Romosinuano and Angus heifers. Brahman sire and dam breed chute temperament scores were greater ( P < 0.05) than those of all other breed groups. Estimates of heterosis for age at first conception were 53.7 9.5 (11%), 56 10.1 (11%), and 92.9 11 d (18%) for Romosinuano-Brahman, Romosinuano-An- gus, and Brahman-Angus, respectively ( P < 0.01). Het- erosis was detected ( P < 0.04) for Romosinuano-Brah- man for BW (12 4.3 kg, 3.7%) and hip height (1.3 0.6 cm, 1%) at first conception. Maternal heterosis for calf birth weight was 3.6 0.5 (12%) and 2.4 0.6 kg (8.6%) for Romosinuano-Angus and Brahman-Angus. In Romosinuano-Brahman and Brahman-Angus, het- erosis for exit velocity was 0.23 0.09 (10%) and 0.5 0.1 m/s (21%). The direct breed effect of Romosinu- ano was to reduce age (58.2 18.9 d), BW (57.6 10.5 kg), and hip height (2.6 1.1 cm) at the time of first conception ( P < 0.01), and the direct Brahman effects ( P < 0.001) were large and numerically positive for these traits (169.8 20.8 d, 93.3 11.6 kg, and 14 1.2 cm). Use of Romosinuano in crossbreeding programs with Brahman may be useful for decreasing the age at first conception. The larger birth weights of calves born to Romosinuano-Angus cross heifers would not be desirable in southern cow-calf operations.not be desirable in southern cow-calf operations....
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