Johnson C R, Lalman D L, Brown M A, Appeddu L A, Buchanan D S, Wettemann R P
Department of Animal Science, Oklahoma State University, Stillwater 74078, USA.
J Anim Sci. 2003 Jul;81(7):1837-46. doi: 10.2527/2003.8171837x.
Brangus cows (n = 29) were used in three experiments to evaluate the effects of parity (multiparous vs. primiparous) and potential genetic merit for milk production (high vs. low) on forage intake during late gestation, early lactation, and late lactation. Cows were selected for milk production based on their sire's EPD for milk production (MEPD). Cows had ad libitum access to (130% of previous 2-d average intake) low-quality hay (5.3% CP and 76% NDF), and cottonseed meal was supplemented to ensure adequate degradable intake protein. All females were adapted to diets for at least 7 d, and individual intake data were collected for 9 d. During the lactation trials, actual milk production was determined using a portable milking machine following a 12-h separation from calves. During late gestation, multiparous cows consumed 24% more (P = 0.01) forage DM (kg/d) than primiparous cows; however, parity class did not influence forage intake when intake was expressed relative to BW. Furthermore, MEPD did not influence forage intake during late gestation. During early lactation, multiparous cows produced 66% more (P < 0.001) milk than primiparous cows, and high MEPD tended (P = 0.10) to produce more milk than low MEPD. Multiparous cows consumed 19% more (P < 0.0001) forage DM than did primiparous cows when expressed on an absolute basis, but not when expressed on a BW basis. High-MEPD cows consumed 8% more (P < 0.05) forage DM than did low-MEPD cows. During late lactation, multiparous cows produced 84% more milk than primiparous cows, although MEPD did not influence (P = 0.40) milk yield. In addition, multiparous cows consumed 17% more (P < 0.01) forage DM per day than primiparous cows, but when intake was expressed relative to BW, neither parity nor MEPD influenced forage DMI during late lactation. Milk yield and BW explained significant proportions of the variation in forage DMI during early and late lactation. Each kilogram increase in milk yield was associated with a 0.33- and 0.37-kg increase in forage DMI for early and late lactation, respectively. Results suggest that multiand primiparous cows consume similar amounts of low-quality forage DM, expressed per unit of BW, during late gestation and lactation. Selecting beef cows for increased genetic merit for milk production increases forage DMI during early lactation.
选用29头布伦格斯母牛进行了三项试验，以评估胎次（经产与初产）和产奶潜在遗传价值（高与低）对妊娠后期、泌乳早期和泌乳后期采食量的影响。根据公牛的产奶预期子代差异（MEPD）选择产奶母牛。母牛可自由采食（为前2天平均采食量的130%）低质量干草（粗蛋白含量5.3%，中性洗涤纤维含量76%），并补充棉籽粕以确保有足够的可降解摄入蛋白。所有母牛至少7天适应日粮，并收集9天的个体采食量数据。在泌乳试验期间，使用便携式挤奶机在与犊牛分离12小时后测定实际产奶量。在妊娠后期，经产母牛的粗饲料干物质采食量（千克/天）比初产母牛多24%（P = 0.01）；然而，当采食量以相对于体重表示时，胎次类别对粗饲料采食量没有影响。此外，妊娠后期MEPD对粗饲料采食量没有影响。在泌乳早期，经产母牛的产奶量比初产母牛多66%（P < 0.001），高MEPD的母牛产奶量往往（P = 0.10）比低MEPD的母牛多。以绝对量表示时，经产母牛的粗饲料干物质采食量比初产母牛多19%（P < 0.0001），但以体重表示时则不然。高MEPD母牛的粗饲料干物质采食量比低MEPD母牛多8%（P < 0.05）。在泌乳后期，经产母牛的产奶量比初产母牛多84%，尽管MEPD对产奶量没有影响（P = 0.40）。此外，经产母牛每天的粗饲料干物质采食量比初产母牛多17%（P < 0.01），但当采食量以相对于体重表示时，胎次和MEPD在泌乳后期均不影响粗饲料干物质采食量。产奶量和体重解释了泌乳早期和后期粗饲料干物质采食量变化的很大比例。泌乳早期和后期，每增加1千克产奶量，粗饲料干物质采食量分别增加0.33千克和0.37千克。结果表明，在妊娠后期和泌乳期，经产和初产母牛每单位体重消耗的低质量粗饲料干物质数量相似。选择产奶遗传价值更高的肉牛母牛会增加泌乳早期的粗饲料干物质采食量。
