Department of Animal and Range Sciences, New Mexico State University, Las Cruces 88003, USA.
J Anim Sci. 2011 Oct;89(10):3334-43. doi: 10.2527/jas.2010-3286. Epub 2011 May 27.
Reproductive performance in young beef cows is often compromised due to a mismatch of physiological demands and suboptimal environmental conditions. Studies conducted at the Corona Range and Livestock Research Center from 2000 to 2007 evaluated 3 postpartum supplement strategies that varied in the amount of glucogenic potential (GP) supplied. Reproductive variables, milk production, and serum metabolites were used to assess supplement effectiveness and economics associated with 2- and 3-yr-old beef cows (n = 379) grazing native range. Supplements were individually fed twice/week at 1,135 g/d (2003 to 2004) or 908 g/d (all other years) and provided 1) 327 g of CP, 109 to 118 g of RUP (CON); 2) 327 to 341 g of CP, 142 to 157 g of RUP (RUP); or 3) 327 g of CP, 151 to 173 g of RUP + 40 to 100 g of propionate salt (PS; RUP+PS). Ultimately, total GP for CON, RUP, and RUP+PS was 44 to 47, 57 to 70, and 93 to 141 g, respectively. Blood samples were collected once/week (2000) or twice/week (2001 to 2007) for progesterone analysis to estimate days to resumption of estrus. Cows were exposed to bulls for 60 d or less, and pregnancy was confirmed by rectal palpation at weaning. Days to resumption of estrus after calving decreased linearly (P = 0.02), resulting in an increased pregnancy rate (P = 0.03) with increasing GP. Milk production exhibited a quadratic (P = 0.04) response to increasing GP, with cows fed RUP producing the most amount of milk. However, a linear decrease (P = 0.07) in days from BW nadir to estrus was found with increasing GP. Total kilograms of calf weaned per cow exposed for the supplemental year and subsequent year was increased linearly (P = 0.07) with increased GP. The improvement in pregnancy rate by supplementing RUP+PS resulted in an increase in total revenue of 18% compared with CON-fed cows and 9.5% compared with RUP-fed cows in the subsequent year after supplementation. These data suggest feeding young cows additional GP in the form of PS allows for partitioning of nutrients away from milk production and toward reproduction, allowing for increased profitability by increasing pregnancy rates and decreasing days to resumption of estrus.
年轻肉牛的繁殖性能常常受到生理需求和环境条件不佳的影响。2000 年至 2007 年在科罗纳牧场和牲畜研究中心进行的研究评估了 3 种产后补充策略，这些策略在提供的生糖潜能（GP）量上有所不同。繁殖变量、牛奶产量和血清代谢物用于评估与放牧原生牧场的 2 岁和 3 岁肉牛（n = 379）相关的补充剂的有效性和经济性。补充剂每周两次单独喂食，每次 1135 克（2003 年至 2004 年）或 908 克（所有其他年份），并提供 1）327 克 CP、109 至 118 克可利用瘤胃蛋白（RUP；CON）；2）327 至 341 克 CP、142 至 157 克 RUP（RUP）；或 3）327 克 CP、151 至 173 克 RUP+40 至 100 克丙酸盐盐（PS；RUP+PS）。最终，CON、RUP 和 RUP+PS 的总 GP 分别为 44 至 47、57 至 70 和 93 至 141 克。每周采集一次（2000 年）或两次（2001 年至 2007 年）血样进行孕激素分析，以估算重新发情的天数。牛群接受公牛配种的时间少于 60 天，断奶时通过直肠触诊确认怀孕。产后重新发情的天数呈线性减少（P = 0.02），随着 GP 的增加，怀孕率增加（P = 0.03）。牛奶产量对 GP 的增加呈二次曲线（P = 0.04）反应，喂 RUP 的奶牛产奶量最多。然而，随着 GP 的增加，从 BW 最低点到发情的天数呈线性减少（P = 0.07）。在补充年和随后的一年中，每头暴露的奶牛断奶的总小牛数呈线性增加（P = 0.07），随着 GP 的增加而增加。与 CON 喂养的奶牛相比，用 RUP+PS 补充 RU 的怀孕率提高了 18%，与 RUP 喂养的奶牛相比，在补充后的次年提高了 9.5%。这些数据表明，以 PS 的形式为年轻奶牛提供额外的 GP，可以将营养物质从产奶中分离出来，转向繁殖，从而通过提高怀孕率和减少重新发情的天数来提高盈利能力。
