J Anim Sci. 2017 Dec;95(12):5301-5308. doi: 10.2527/jas2017.1780.
The objective of this study was to determine the effect of stockpiled forage type and protein supplementation on VFA production, serum metabolites, and BW in yearling beef heifers. Over 2 yr, spring-born, Angus crossbred yearling beef heifers ( = 42; 305 ± 2.9 kg initial BW) were randomly assigned to 1 of 3 forage pasture types: 1) endophyte-infected tall fescue [TF; (Schreb.) Dumort], 2) a big bluestem ( Vitman) and indiangrass ( L.) combination (BI), or 3) switchgrass (SG; L.). Each pasture was then randomly assigned to receive either 1 of 2 isonitrogenous CP treatments: 1) 0.68 kg·heifer·d of dried distiller's grains with solubles (DDGS; 28% CP and 88% TDN) or 2) 0.22 kg·heifer·d of blood meal and fish meal (BF; 72.5% CP and 69.5% TDN), resulting in a 3 × 2 factorial arrangement of treatments. Treatments were initiated in January and terminated in April in both years of the study. Body weights and blood samples were collected approximately every 28 d from initiation of grazing until the end of the trial. Heifer BW change from January to February and overall BW change were greater ( < 0.01) for TF heifers. However, BW change from March to April was not different ( = 0.84) among forage types. Supplement type did not influence ( ≥ 0.13) BW or BW change from January to February and from January to April; however, heifers fed DDGS had greater ( = 0.03) BW gain from March to April. Heifer BW change from February to March exhibited ( < 0.05) a forage type × supplement interaction, with BF-fed heifers gaining more BW on BI pastures than DDGS-fed heifers. Serum glucose concentrations, ruminal acetate, and the acetate:propionate ratio were greater ( ≤ 0.04) for SG heifers. However, circulating serum NEFA and urea N (SUN) concentrations were not different ( ≥ 0.85) among forage types. Serum glucose and NEFA concentrations were not influenced ( ≥ 0.61) by supplement type. Circulating SUN concentrations were greater ( < 0.01) in BF-supplemented heifers. Ruminal acetate tended to be greater ( = 0.09) and butyrate concentrations were greater ( < 0.01) for BF-supplemented heifers. The acetate:propionate ratio was not influenced ( = 0.15) by supplement type. These results suggest that a compensatory gain period prior to breeding would be needed for these native warm-season species to be a viable opportunity for growing and developing replacement heifers in the southeastern United States.
本研究的目的是确定储备饲料类型和蛋白质补充对 VFA 产生、血清代谢物和育肥牛小母牛体重的影响。在 2 年的时间里，春季出生的安格斯杂交育肥牛小母牛（n = 42；初始体重 305 ± 2.9 kg）被随机分配到 3 种牧草牧场类型之一：1）内生真菌感染的高羊茅[TF；（Schreb.）Dumort]，2）大须芒草（Vitman）和印第安草（L.）组合（BI），或 3）柳枝稷（SG；L.）。每个牧场随后被随机分配接受 2 种等氮 CP 处理之一：1）0.68 kg·heifer·d 干酒糟及其可溶物（DDGS；28% CP 和 88% TDN）或 2）0.22 kg·heifer·d 血粉和鱼粉（BF；72.5% CP 和 69.5% TDN），导致处理的 3×2 因子排列。在研究的两年中，处理在 1 月开始并在 4 月结束。从放牧开始到试验结束，每隔 28 天左右采集体重和血液样本。TF 小母牛的体重从 1 月到 2 月的变化和总体体重变化更大（<0.01）。然而，从 3 月到 4 月的体重变化在牧草类型之间没有差异（=0.84）。补充类型不影响（≥0.13）体重或从 1 月到 2 月和从 1 月到 4 月的体重变化；然而，DDGS 喂养的小母牛从 3 月到 4 月的体重增加更多。从 2 月到 3 月的小母牛体重变化表现出（<0.05）牧草类型×补充剂的相互作用，BF 喂养的小母牛在 BI 牧场上的体重增加多于 DDGS 喂养的小母牛。SG 小母牛的血清葡萄糖浓度、瘤胃乙酸和乙酸：丙酸比更大（≤0.04）。然而，血清中游离 NEFA 和尿素氮（SUN）浓度在牧草类型之间没有差异（≥0.85）。补充剂类型不影响（≥0.61）血清葡萄糖和 NEFA 浓度。SUN 浓度在 BF 补充的小母牛中更高（<0.01）。瘤胃乙酸的浓度趋于更高（=0.09），丁酸的浓度更高（<0.01），在 BF 补充的小母牛中。乙酸：丙酸比不受补充剂类型的影响（=0.15）。这些结果表明，对于这些本地暖季物种，在繁殖前需要一个补偿性生长期，才能成为美国东南部育肥牛小母牛的可行机会。
