Dairy Science Department, Virginia Polytechnic Institute and State University, Blacksburg 24061.
Virginia Maryland Regional College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg 24061.
J Dairy Sci. 2019 Sep;102(9):8502-8512. doi: 10.3168/jds.2019-16450. Epub 2019 Jul 3.
Diet is known to affect rumen growth and development. Calves fed an all-liquid diet have smaller and less developed rumens and a decreased ability to absorb volatile fatty acids (VFA) compared to calves fed both liquid and dry feed. However, it is unknown how rumens respond when challenged with a defined concentration of VFA. The objective of this study was to assess the effects of 2 different feeding programs on VFA absorption in preweaned calves. Neonatal Holstein bull calves were individually housed and randomly assigned to 1 of 2 diets. The diets were milk replacer only (MRO; n = 5) or milk replacer with starter (MRS; n = 6). Diets were isoenergetic (3.87 ± 0.06 Mcal of metabolizable energy per day) and isonitrogenous (0.17 ± 0.003 kg/d of apparent digestible protein). Milk replacer was 22% crude protein, 21.5% fat (dry matter basis). The textured calf starter was 21.5% crude protein (dry matter basis). Feed and ad libitum water intakes were recorded daily. Calves were exposed to a defined concentration of VFA buffer (acetate 143 mM, propionate 100 mM, butyrate 40.5 mM) 6 h before euthanasia on d 43 ± 1. Rumen fluid samples were obtained every 15 to 30 min for 6 h to measure the rate of VFA absorption. Rumen tissues were obtained from the ventral sac region and processed for morphological and immunohistochemical analyses of the VFA transporters monocarboxylate transporter 1 (MCT1) and 4 (MCT4). Body growth did not differ between diets, but empty reticulorumens were heavier in MRS than MRO calves (0.67 vs. 0.39 ± 0.04 kg) and MRS calves had larger papillae areas (0.76 vs. 15 ± 0.08 mm). We observed no differences between diets in terms of the abundance of MCT1 and MCT4 per unit area. These results indicate that the extrapolated increase in total abundance of MCT1 or MCT4 in MRS calves was not due to increased transporter density per unit area. Modeled VFA absorption metrics (flux, mmol/h, or 6 h absorbed VFA in mmol) were not different across diets. These results demonstrate that the form of calfhood diet, whether solely MR or MR and starter, does not alter VFA absorption capacity when the rumen is exposed to a defined concentration of VFA at 6 wk of age.
饮食已知会影响瘤胃的生长和发育。与同时喂食液体和固体饲料的小牛相比，仅喂食全液体饲料的小牛的瘤胃更小、发育程度更低，且吸收挥发性脂肪酸 (VFA) 的能力也降低。然而，当瘤胃受到特定浓度的 VFA 挑战时，其反应方式尚不清楚。本研究的目的是评估 2 种不同的饲养方案对未断奶小牛 VFA 吸收的影响。将新生荷斯坦公牛小牛单独饲养，并随机分配到 2 种饮食中的 1 种。这 2 种饮食分别为仅代乳料（MRO；n = 5）或代乳料加开食料（MRS；n = 6）。饮食的能量值相同（每天 3.87 ± 0.06 兆卡代谢能），且氮含量也相同（每天 0.17 ± 0.003 千克表观可消化蛋白）。代乳料的粗蛋白含量为 22%，脂肪含量为 21.5%（干物质基础）。质地柔软的小牛开食料的粗蛋白含量为 21.5%（干物质基础）。每天记录饲料和自由饮水的摄入量。在第 43 ± 1 天处死小牛前 6 小时，小牛会接触到特定浓度的 VFA 缓冲液（乙酸盐 143 mM，丙酸盐 100 mM，丁酸盐 40.5 mM）。每 15 至 30 分钟收集 6 小时的瘤胃液样本，以测量 VFA 的吸收速率。从腹囊区域获得瘤胃组织，并进行单羧酸转运蛋白 1 (MCT1) 和 4 (MCT4) 的形态学和免疫组织化学分析，以评估 VFA 转运体。2 种饮食对小牛的体生长没有影响，但 MRS 小牛的空瘤胃重量比 MRO 小牛更重（0.67 比 0.39 ± 0.04 千克），且 MRS 小牛的乳头面积更大（0.76 比 15 ± 0.08 毫米）。我们在每单位面积的 MCT1 和 MCT4 丰度方面没有观察到饮食之间的差异。这些结果表明，MRS 小牛中 MCT1 或 MCT4 的总丰度的推断增加并不是由于单位面积的转运蛋白密度增加所致。不同饮食的 VFA 吸收量（流量、mmol/h 或 6 h 内吸收的 VFA mmol）没有差异。这些结果表明，当小牛在 6 周龄时接触到特定浓度的 VFA 时，其幼年期的饮食形式（仅代乳料或代乳料和开食料）并不会改变 VFA 的吸收能力。
