Animal Nutrition Group, Wageningen University, PO Box 338, 6700 AH Wageningen, The Netherlands.
J Dairy Sci. 2012 Nov;95(11):6654-64. doi: 10.3168/jds.2012-5463. Epub 2012 Sep 7.
This study was designed to quantify the contribution of low-protein solid feed (SF) intake, in addition to milk replacer, to protein and energy retention in veal calves. Because of potential interactions between milk replacer and SF, occurring at either the level of digestion or postabsorption, this contribution might differ from that in calves fed either SF or milk replacer alone. Forty-eight Holstein Friesian male calves, 55±0.3 kg of body weight (BW), were divided across 16 groups of 3 calves each. Groups were assigned randomly to 1 of 4 incremental levels of SF intake: 0, 9, 18, or 27 g of DM of SF/kg of BW(0.75) per day. The SF mixture consisted of 25% chopped wheat straw, 25% chopped corn silage, and 50% nonpelleted concentrate (on a DM basis). Each group was housed in a respiration chamber for quantification of energy and N balance at each of 2 BW: at 108±1.1 kg and at 164±1.6 kg. The milk replacer supply was 37.3g of DM/kg of BW(0.75) per day at 108 kg of BW and 40.7 g of DM/kg of BW(0.75) per day at 164 kg of BW, irrespective of SF intake. Within a chamber, each calf was housed in a metabolic cage to allow separate collection of feces and urine. Indirect calorimetry and N balance data were analyzed by using regression procedures with SF intake-related variables. Nitrogen excretion shifted from urine to feces with increasing SF intake. This indicates a higher gut entry rate of urea and may explain the improved N utilization through urea recycling, particularly at 164 kg of BW. At 108 kg of BW, the gross efficiency of N retention was 61% for calves without SF, and it increased with SF intake by 5.4%/g of DM of SF per day. At 164 kg of BW, this efficiency was 49% for calves without SF, and it increased by 9.9%/g of DM of SF per day. The incremental efficiency of energy retention, representing the increase in energy retained per kilojoule of extra digestible energy intake from SF, was 41% at 108 kg of BW and 54% at 164 kg of BW. Accordingly, the apparent total-tract digestibility of NDF increased with BW, from 46% at 108 kg of BW to 56% at 164 kg of BW. On average, 5.5% of gross energy from SF was released as CH(4) in veal calves, which is similar to reported values in cattle fed only SF. In conclusion, the provision of low-protein SF resulted in improved N utilization for protein gain, particularly toward the end of the fattening period. In heavy calves, recycling of urea originating from amino acids in milk replacer potentially contributes substantially to the N retention of veal calves fed SF.
这项研究旨在量化除了代乳料之外，低蛋白固体饲料（SF）摄入对小牛肉牛的蛋白质和能量保留的贡献。由于代乳料和 SF 之间可能存在相互作用，无论是在消化水平还是在吸收后水平，这种贡献可能与单独喂食 SF 或代乳料的小牛不同。48 头荷斯坦弗里生雄性小牛，体重 55±0.3 公斤，分为 16 组，每组 3 头。将组随机分配到 SF 摄入的 4 个递增水平之一：0、9、18 或 27 g 的 DM 的 SF/kg 的 BW(0.75)每天。SF 混合物由 25%切碎的小麦秸秆、25%切碎的玉米青贮和 50%非颗粒浓缩物（以 DM 为基础）组成。每组都被安置在一个呼吸室中，以在 2 个 BW 下定量测量能量和 N 平衡：在 108±1.1 公斤和 164±1.6 公斤时。代乳料供应量为每天 37.3g 的 DM/kg 的 BW(0.75)，在 108 公斤 BW 时，每天 40.7 g 的 DM/kg 的 BW(0.75)，不论 SF 摄入量如何。在室内，每头小牛都被安置在代谢笼中，以便单独收集粪便和尿液。通过使用与 SF 摄入相关的变量的回归程序分析间接测热法和 N 平衡数据。随着 SF 摄入的增加，氮排泄从尿液转移到粪便。这表明尿素的肠道进入率更高，这可能解释了通过尿素再循环提高氮的利用率，尤其是在 164 公斤 BW 时。在 108 公斤 BW 时，无 SF 的小牛的氮保留总效率为 61%，随着 SF 摄入的增加，每天增加 5.4%/g 的 DM 的 SF。在 164 公斤 BW 时，无 SF 的小牛的效率为 49%，每天增加 9.9%/g 的 DM 的 SF。能量保留的增量效率，代表每摄入 1 千焦耳可消化能量来自 SF 保留的能量增加，在 108 公斤 BW 时为 41%，在 164 公斤 BW 时为 54%。相应地，NDF 的总肠道消化率随着 BW 的增加而增加，从 108 公斤 BW 时的 46%增加到 164 公斤 BW 时的 56%。平均而言，SF 中 5.5%的总能量以 CH(4)的形式释放，这与仅喂食 SF 的牛的报告值相似。总之，提供低蛋白 SF 可提高蛋白质生长的氮利用率，特别是在育肥期结束时。在大体重的小牛中，来自代乳料中氨基酸的尿素再循环可能对 SF 喂养的小牛的氮保留有很大贡献。
