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Title: Feed efficiency of tropically adapted cattle when fed in winter or spring in a temperate location

item COLEMAN, SAMUEL - Retired ARS Employee
item Chase, Chadwick - Chad
item PHILLIPS, WILLIAM - Retired ARS Employee
item RILEY, DAVID - Texas A&M University

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/4/2018
Publication Date: 6/4/2018
Citation: Coleman, S.W., Chase, C.C., Phillips, W.A., Riley, D.G. 2018. Feed efficiency of tropically adapted cattle when fed in winter or spring in a temperate location. Journal of Animal Science. 96:2438–2452.

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. While Brahman and particularly F1 Brahman x English cows have proven to be ideal brood cows for the subtropics, Brahman-influenced calves are usually discounted at weaning because of perceptions for poor performance and efficiency during finishing. This study was conducted by ARS scientists in Brooksville, FL and El Reno, OK to evaluate steer calves of varying level of Brahman or Romosinuano (tropical) influence when crossed with Angus at weaning, during winter growing and spring finishing. While tropical adaptation in the cow herd is necessary for optimum production in the southeast and Gulf Coast areas of the US, proportion of tropical breeding is a disadvantage for both performance and efficiency in the winter of temperate regions for growing/finishing cattle of high proportion tropical genetics. However, steers with 50% tropical genetics were productive and efficient, and F1 cows such as the Brahman x Romosinuano provides tropical adaptation and maternal heterosis for the cow herd suited for regions such as the SE USA and Gulf Coast, and when bred to temperately adapted B. taurus breeds, produce a calf that is suitable for excellent productivity in temperate regions. The results of this study provide information on how best to manage cattle that must spend part of their life-cycle in different climatic regions.

Technical Abstract: Earlier work has shown that young, tropically adapted cattle do not gain as rapidly as temperately adapted cattle during the winter in OK. The objective for this study was to determine if efficiency of gains was also impacted in tropically adapted cattle and if efficiency is consistent in different seasons. Over 3 yr, 239 straightbred and crossbred steers (F1 and three-way crosses) of Angus, Brahman or Romosinuano breeding, born in Brooksville, FL were transported to El Reno, OK in October and fed in two phases to determine performance, individual intake and efficiency. Phase 1 (WIN) began in November after a 28 d recovery from shipping stress and Phase 2 (SS) began in March, 28 d following completion of WIN each year. The diet for WIN was a grower diet (14% CP, 1.10 Mcal NEg/kg) and that for the SS was a conventional feedlot diet (12.8% CP; 1.33 Mcal NEg/kg). Intake trials were conducted with 14 d adjustment to diet and facilities and from 56 to 162 d for determination of intake and gain for efficiency. Body weights were recorded at approximately 14 d intervals, and initial BW, median BW, and ADG were from individual animal regressions of BW on days on feed (DOF). Individual daily DM intake was then regressed by phase on median body weight and ADG, and errors of regression were recorded as residual feed intake (RFI). Similarly, daily gain was regressed by phase on median body weight and DM intake, and errors of regression were recorded as residual gain. Gain to feed (GF) was also calculated as a measure of efficiency. The statistical model to evaluate ADG, DM intake, and efficiency included fixed effects of year, damage (3 to 4, 5, 6 to10, and > 10yr), harvest group (3 per year), age on test, and a nested term DT(ST x XB) where DT = proportion tropical breeding of dam (0, 0.5, or 1), ST= proportion tropical breeding of sire (1, or 0), and XB whether the calf was straightbred or crossbred. Sire(ST x XB) and pen were random effects. In the WIN, 100% tropical steers gained more slowly and were less efficient (gain to feed ratio) than steers with some Angus breeding (P < 0.01), but no differences occurred in RFI. Crossbred steers had lower (P < 0.05) RFI in SS than straightbred steers, and Angus sired crossbred steers were more efficient (P < 0.01) than other sire groups. Simple correlations, both Pearson and Spearman, between RFE in WIN and SS were 0.51 (P < 0.01) whereas that for gain to feed ratio was 0.20 (P < 0.01).