IDENTIFICATION AND UTILIZATION OF MECHANISMS RESPONSIBLE FOR THE ADAPTATION OF CATTLE TO STRESSORS OF THE SUBTROPICS
Title: Evaluation of tropically-adapted straightbred and crossbred beef cattle: Heifer age and size at first conception and characteristics of their first calves
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 15, 2010
Publication Date: October 1, 2010
Citation: Riley, D.G., Chase, C.C., Coleman, S.W., Olson, T.A., Randel, R.D. 2010. Evaluation of tropically-adapted straightbred and crossbred beef cattle: Heifer age and size at first conception and characteristics of their first calves. Journal of Animal Science. 88:3173-3182.
Interpretive Summary: Cow-calf producers in the Southern United States have utilized Brahman crossbreds at least in part because of their superior adaptability and excellent reproduction in the harsh environmental conditions of the region. However, Brahman straightbreds are necessary to produce crossbred females and some of the performance and handling challenges associated with these include late sexual maturation relative to other breeds of cattle and poor temperament. Adapted Bos taurus females may reach puberty sooner and be more docile than Brahman and may represent a crossbreeding opportunity (with Brahman) to improve these aspects of cow-calf production while still having a female that is adapted to the hot, humid conditions of the region. ARS researchers at Brooksville, FL with collaborators at the University of Florida and Texas A&M University evaluated the Romosinuano, a Criollo breed from South America, for age, weight, and hip height at the estimated time of first conception (puberty), birth weight, vigor and mortality of calves, and assessments of calving difficulty and of temperament in heifers produced from matings of Romosinuano, Brahman, and Angus cattle. Brahman heifers were older, heavier, and had greater hip height than other straightbred groups and most crossbred groups at puberty. Brahman and reciprocal Brahman-Angus heifers had greater exit velocity than Romosinuano and Angus heifers indicating they were more excitable. Heterosis for age at puberty was evident for all breed combinations and ranged from -54 to -93 days, the greatest for Brahman-Angus crosses. In breeding programs, the Romosinuano breed may offer earlier reproductive success and calmer temperament relative to the American Brahman. These would be advantageous to Southern U.S. cow-calf producers if females perform similarly to Brahman in terms of longevity and lifetime productivity.
The objectives of this work were to estimate genetic effects for age and size at estimated time of first conception, and temperament in straightbred and crossbred heifers (n = 554) produced from Romosinuano, 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 mortality. At approximately 7 mo of age, weaned heifers were pastured with Mashona or Tuli bulls until confirmed pregnant. 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 employed to estimate weight 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 higher (P < 0.05) than 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-Angus, and Brahman-Angus, respectively (P < 0.01). Heterosis was detected (P < 0.04) for Romosinuano-Brahman for weight (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, heterosis for exit velocity was 0.23 ± 0.09 (10%) and 0.5 ± 0.1 m/s (21%). The direct breed effect of Romosinuano was to lower age (–58.2 ± 18.9 d), weight (–57.6 ± 10.5 kg), and hip height (–2.6 ± 1.1 cm) at time of first conception (P < 0.01), and the direct 46 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 age at first conception. The high birth weights of calves born to Romosinuano-Angus cross heifers would not be desirable in Southern cow-calf operations.