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A R Wiseman, M D Redden, C M Spencer, A L McGee, R Reuter, D L Lalman, 23 Effects of Timing of Weaning on Calf Performance and Maintenance Energy Requirements in Primiparous Beef Cows., Journal of Animal Science, Volume 96, Issue suppl_1, March 2018, Pages 12–13, https://doi.org/10.1093/jas/sky027.024
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Abstract
Early weaning is used to minimize cow nutrient requirements in situations where feed inputs are scarce or expensive. For many years, maintenance energy requirements have been assumed to be 20% greater in lactating compared to dry beef cows. While not well established, maintenance energy requirements are thought to be greatest in primiparous cows and to decline with age. Consequently, early weaning primiparous cow/calf pairs should benefit system efficiency, particularly in situations where mid- to late-lactation forage or feed nutritive value is moderate or low. The objective of this study was to determine the biological efficiency of early weaning and maintenance energy requirements of lactating vs non-lactating primiparous dams. Experiments were conducted in two consecutive years using 90 primiparous heifers and their calves (48 in yr 1, 42 in yr 2). Pairs were assigned to one of two treatments; early weaning (EW, 130 d ± 15.4) and traditional weaning (TW, 226 d ± 13.1) with three pen replications per treatment each year (8 pairs/pen yr 1, 7 pairs/pen yr 2). Late-lactation cow and calf performance and feed consumption was measured for 92 d (yr 1) and 100 d (yr 2). Cows were limit-fed to meet maintenance requirements, while calves were offered ad libitum access to the same diet in a creep feeding area. Calves were not allowed access to the cows’ feed. Cow feed intake, body condition score, body weight, milk yield and composition, and calf body weight gain and creep feed intake were recorded. Calf ADG (P<0.001) was significantly greater for TW calves. The efficiency of energy utilization varied depending on how it was expressed. Calf gain to Mcal creep feed and milk energy was greater (P=0.03) for the EW calves. In contrast, calf gain to Mcal of creep intake (P<0.001) and calf gain to Mcal of feed intake of the pair (P=0.002) was greater for the TW calves. After accounting for lactation and retained energy, there was no difference in maintenance energy requirements of primiparous cows (P=0.95). With no additional maintenance costs in lactating primiparous cows and improved calf performance, the TW system was more efficient at converting total feed energy to kg of calf body weight gain.
