IDENTIFICATION AND UTILIZATION OF MECHANISMS RESPONSIBLE FOR THE ADAPTATION OF CATTLE TO STRESSORS OF THE SUBTROPICS
Title: Evaluation of tropically adapted straightbred and crossbred cattle: Postweaning gain and feed efficiency when finished in a temperate climate
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 13, 2012
Publication Date: June 1, 2012
Citation: Coleman, S.W., Chase, C.C., Jr., Phillips, W.A., Riley, D.G., Olson, T.A. 2012. Evaluation of tropically adapted straightbred and crossbred cattle: Postweaning gain and feed efficiency when finished in a temperate climate. Journal of Animal Science. 90:1955-1965.
Interpretive Summary: About 38% of the nation’s cow herd is located in the southeastern and Gulf Coast region of the U.S.A. but cattle production in this subtropical region has unique problems associated with heat, humidity, parasite and disease exposure, and a seasonally-impacted feed supply. While cattle in the region must be acclimated to these stressors, their calves are often grown and finished in a more temperate environment. Brahman and particularly F1 Brahman x English cows have proven to be ideal brood cows for the subtropics, and for most traits, Brahman ' Bos taurus crossbreds express greater heterosis than B. taurus crossbreds. However, Brahman-influenced calves are usually discounted at weaning because of perceptions for poor performance and efficiency during finishing. Tropically adapted B. taurus breeds of cattle such as the the Criollo breeds from Central and South America may offer sufficient adaptation as alternatives to or in combination with the Brahman for cow-calf production in the Gulf Coast region. ARS scientists in Brooksville, FL and El Reno, OK collaborated to evaluate the Criollo breed, Romosinuano, from South America as purebreds and F1 crosses with Brahman and Angus during the postweaning growth and finishing phases of production. Tropically adapted Brahman and Romosinuano and their crosses were heavier than Angus and their crosses at weaning in FL, but gained more slowly in OK during the winter while grazing wheat pasture. Rate of gain and body weight in the spring were linearly related to the proportion of tropical genetics of an animal. During the finishing phase beginning in May each year, gains were not different among breed types. Heterosis (hybrid vigor) for gain and weight were almost twice as great for Brahman-Angus crosses as for the other crosses. However, we did not find evidence for heterosis for feed efficiency among any crosses. These data would suggest that if cold weather is the cause, then tropically adapted cattle should be wintered in more southerly climates before finishing in temperate zones.
Beef cows in the subtropical USA must be adapted to the stressors of the environment, typically supplied by using percentage Brahman breeding. Calves produced in the region, however, are usually grown and finished in more temperate regions, and have a perceived reputation for poor BW gains and feed efficiency during finishing. Compromised fertility and carcass quality often associated with the Brahman have increased interest in tropically adapted Bos taurus breed types. The objective of this study was to evaluate three breeds [A=Angus(Bos taurus – temperate); B=Brahman(B. indicus – tropical); and R=Romosinuano (B. taurus – tropical)] and all possible crosses during various segments of post-weaning growth, and for feed efficiency during the finishing phase. Steer calves (n = 435) born over three years were weaned in late September, backgrounded for at least 21 d (BKG), shipped 2025 km to El Reno, OK in October, fed a preconditioning diet for 28 d (RCV), grazed wheat pasture from Nov. to May (WHT), finished on a conventional feedlot diet (FIN), and serially slaughtered after approximately 95, 125, and 150 days on feed. Weight and ADG during each segment were tested using a mixed model that included calf age at weaning, year (Y), breed of sire (SB) and breed of dam (DB), and interactions. In addition, winter treatment (continuous wheat or reduced grazing of wheat with supplement) was included for the wheat and feedlot phases. Sire within SB x SB [and pen (barn x year) for feedlot phase] were considered random. The SB x DB interaction was the effect of interest and was significant for all traits (P < 0.01) except exit velocity taken at weaning and ADG during FIN, but both traits were affected by 3-way interactions with Y or harvest group. Tropically-adapted purebred steers had higher ADG through weaning and BKG in FL but the reverse was true during the RCV and WHT segments. Similar, but less pronounced results were noted for F1 steers with 100% tropical influence compared to those with only 50%. Heterosis was greatest for AxB (11 to 64%) and similar for AxR and BxR (3 to 42%) for most traits. The largest estimates for heterosis were for the short duration BKG and RCV segments. In a subset of the steers (n=261) neither ADG nor feed efficiency was influenced by level of tropical breeding, and heterosis was not evident for either ADG or feed efficiency. These data show that winter is the period when productivity of tropically adapted cattle is compromised.