Nurture Research Center, Provimi North America, Cargill Animal Nutrition, Brookville, OH 45309.
Nurture Research Center, Provimi North America, Cargill Animal Nutrition, Brookville, OH 45309.
J Dairy Sci. 2019 Mar;102(3):2242-2253. doi: 10.3168/jds.2018-15354. Epub 2019 Jan 26.
Apparent total-tract digestibility data from 3 published studies with calves from 0 to 4 mo of age were used to evaluate National Research Council (NRC; 2001) estimates of digestible energy (DE) and metabolizable energy (ME) in calf starters (CS). Calves (n = 83) or pens of calves (n = 24) were used in model development. In each study, 48 Holstein bull calves (2-3 d of age at initiation of each study) were fed varying amounts of milk replacer with CS and water for ad libitum consumption. Calf starters varied in nutrient composition and physical form (pelleted, textured, or mixed with 5% grass hay and fed as a total mixed ration). Apparent total-tract digestibility was measured at various ages. Feed and feces were collected from 20 calves per trial during 5-d collection periods during the first 56 d of each trial. In 2 studies, calves were grouped in pens (4 calves/pen) for a second 56-d measurement period. Fecal collections were repeated occasionally during the second period. Total-tract digestibilities (n = 207) of neutral detergent fiber, nonfiber carbohydrates (NFC), crude protein (CP), and fat were used to calculate ME in CS using equations from the 2001 Dairy NRC. Contributions of digestible CP and fat from milk replacer before weaning were estimated using nonlinear regression and removed from estimates of fat and CP digestibility in CS. Digestion of most nutrients in CS and calculated DE and ME in CS were low early in life and increased with increasing cumulative NFC intake. The natural logarithm of cumulative NFC intake, measured from d 0 to the end of each digestibility period, accounted for more variation in CS nutrient digestibilities, DE and ME estimates compared with daily NFC intake or intake of other nutrients, intake of milk replacer, or age of calf. Calculated ME values in CS were similar to those predicted by NRC after calves consumed approximately 15 kg of cumulative NFC or 28 kg of cumulative dry matter intake (assuming 53% NFC in CS). Current estimates of energy in CS fed to 4 mo of age may overestimate contribution of dry feed to overall energy metabolism in young calves.
使用来自 0 至 4 月龄犊牛的 3 项已发表研究的表观全肠道消化率数据，评估了国家研究委员会（NRC；2001 年）对犊牛开食料（CS）中可消化能（DE）和代谢能（ME）的估计值。在模型开发中使用了犊牛（n=83）或犊牛栏（n=24）。在每项研究中，48 头荷斯坦公牛犊牛（每项研究开始时 2-3 日龄）用不同量的代乳粉和 CS 以及水自由采食。犊牛开食料的营养成分和物理形式（颗粒状、膨化或与 5%的干草混合并作为全混合日粮饲喂）有所不同。在不同年龄测量表观全肠道消化率。在每项试验的前 56 天期间的 5 天收集期内，从每个试验的 20 头犊牛中收集饲料和粪便。在 2 项研究中，犊牛在栏内分组（4 头犊牛/栏）进行第二个 56 天的测量期。第二个期间偶尔会重复粪便收集。使用 2001 年 NRC 奶牛中的方程，根据中性洗涤纤维、非纤维碳水化合物（NFC）、粗蛋白（CP）和脂肪的全肠道消化率计算 CS 中的 ME。使用非线性回归估计断奶前代乳粉中可消化 CP 和脂肪的贡献，并从 CS 中脂肪和 CP 消化率的估计中去除。CS 中大多数营养素的消化以及计算出的 CS 中 DE 和 ME 在生命早期都很低，并随着累积 NFC 摄入量的增加而增加。从第 0 天到每个消化率期结束时测量的累积 NFC 摄入量的自然对数，与每日 NFC 摄入量或其他营养素、代乳粉摄入量或犊牛年龄相比，能更好地解释 CS 中营养素消化率、DE 和 ME 估计值的变化。当犊牛消耗约 15 kg 累积 NFC 或 28 kg 累积干物质摄入量（假设 CS 中的 NFC 为 53%）后，CS 中的计算 ME 值与 NRC 预测值相似。目前对 4 月龄犊牛饲喂 CS 中的能量估计值可能高估了干饲料对幼犊整体能量代谢的贡献。
