Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/18/2006
Publication Date: 6/1/2006
Citation: Freetly, H.C., Nienaber, J.A., Brown Brandl, T.M. 2006. Changes in heat production by mature cows after changes in feeding level. Journal of Animal Science. 84(6):1429-1438. Interpretive Summary: The cost of feed for the cow herd represents the major production expense associated with beef production. Improving the efficiency with which cows use feed is a potential mechanism for improving production efficiency of beef cattle. Using the cow’s ability to store nutrients in body tissues represents a viable mechanism to improve the economic efficiency of beef production. We determined that acute adaptation of heat production to feed restriction and realimentation occurs within the first seven days. Chronic adaptation to changes in nutrient levels occur over extended periods of time and adaptation to realimentation takes longer than adaptation to feed restriction. These data suggest that rapid increases in body weight of cows that have previously been feed restricted are not the result of a lag in heat production. The efficiency with which a cow will utilize feed will change over time as she adapts to new nutrient levels.
Technical Abstract: We hypothesized that adaptation of heat production in the realimented cow would occur over an extended period of time and the length of time would be influenced by the level of feed. Our objectives were to quantify the changes in heat production of cows following feed restriction and to quantify the affect of level of realimentation on the dynamics of heat production in light weight cows. Forty four-year-old nonpregnant, nonlacting cows (four breed composite cows: 1/4 Hereford, 1/4 Angus, 1/4 Red Poll, and 1/4 Pinzgauer) were randomly assigned to one of four nutrient treatments. All cows were feed restricted (50.0 g DM/kg BW**0.75) and individual calorimetry measurements were taken 7, 13, 28, 56, and 91 d after feed restriction. In refeed period 1, cows were fed their assigned feed level for their treatment after d 91 measurement: 50.0 (T50.0), 58.5 (T58.5), 67.0 (T67.0), and 75.5 (T75.5) g DM/kg BW**0.75. Subsequent measures were taken at 7, 13, 28, 42, 56, 91, 119, and 175 d. In refeed period 2, all cows were fed 75.5 g DM/kg BW**0.75 after their 175 d measurement and measures were taken at 7, 14, 28, 56, and 112 d. In refeed period 1, heat production decreased rapidly during the first 7 d of feed restriction such that HP was 15% lower 7 d after feed restriction. From 28 through 91 d after feed restriction, daily HP decreased linearly (-6.57 +/- 1.35 kcal/d; P < 0.001). The d 7 heat productions increased 9% for T58.5, 12% for T67.0, and 20% for T75.5 over d 0 heat production. From d 7 through d 175, heat production differed between treatments (P < 0.001; Figure 2a) and heat production decreased over time (-1.19 +/- 0.46 kcal/d; P = 0.01). In refeed period 2, 7 d after the increase in feed intake, heat production increased 27% for the T50.0 cows, 13% for the T58.5 cows, and 4% for the T67.0 cows. Treatments did not differ in heat production (P = 0.39; Figure 3a). Daily heat production increased 2.5 kcal/d. These data suggest that there is not a lag in heat production during realimentation and that increased energy retention is associated with an increased heat production.