Department of Animal and Poultry Science, University of Saskatchewan, Saskatoon, SK S7N 5A8, Canada.
J Anim Sci. 2013 Apr;91(4):1685-95. doi: 10.2527/jas.2012-5669. Epub 2013 Feb 19.
The objective of this study was to evaluate whether different severities of short-term feed restriction (FR) affect the absorptive function of the reticulo-rumen and total tract barrier function in beef cattle. Eighteen ruminally cannulated and ovariectomized Angus × Hereford heifers were blocked by BW into 3 blocks, with blocks conducted sequentially. Treatments were imposed during the 5-d FR period by restricting heifers to 75 (FR75), 50 (FR50) or 25% (FR25) of the ad libitum feed intake measured during a 5-d baseline period (BASE) occurring immediately before FR. Throughout the study, heifers were housed in individual pens (9 m(2)) and were fed the same diet (60% forage:40% concentrate) with free access to water. Dry matter intake was measured daily and ruminal pH was measured every 2 min throughout the study. Ruminal fluid and blood samples were collected on d 3 of the BASE and FR periods, and the temporarily isolated and washed reticulo-rumen technique was used to evaluate short-chain fatty acid (SCFA) absorption on d 5 of the BASE and FR periods. Total tract barrier function was evaluated starting on d 2 of the BASE and FR periods using a pulse dose of Cr-EDTA followed by 48 h of total urine collection. Data were analyzed using the Proc Mixed procedure of SAS with the fixed effects of block, treatment, period, and the treatment × period interaction, the random effect of cow nested in block with period included as a repeated measure. Dry matter intake did not differ among treatments during BASE but, as imposed by the experimental model, DMI during FR relative to BASE equated to 70, 49, and 25%, which was close to the targeted values of 75, 50, and 25% (treatment × period, P < 0.001). A treatment × period interaction (P < 0.001) was also detected for ruminal SCFA concentration with the concentration decreasing as the severity of FR increased, whereas there were no differences during BASE. Mean ruminal pH increased during FR with increasing severity of FR, but was not different during BASE (treatment × period, P < 0.001). Absorption of SCFA across the reticulo-rumen tended to decrease with increasing severity of FR (P = 0.08). For individual SCFA, acetate absorption (mmol/h) tended (P = 0.057) to be less for FR25 and FR50 when compared with FR75 and decreased (P = 0.05) by almost 70 mmol/h at FR25 and FR50 relative to BASE (322mmol/h). Heifers restricted to 25% (FR25) feed had greater urinary Cr recovery during FR than BASE, whereas no changes were detected for FR75 and FR50. This study indicates that moderate severities of short-term FR decrease the absorptive function of the reticulo-rumen, but more severe FR is required to compromise total tract barrier function in beef cattle.
本研究旨在评估短期不同程度的限饲（FR）是否会影响肉牛网胃和全肠道屏障功能的吸收功能。18 头经瘤胃切开和卵巢切除术的安格斯×海福特小母牛按体重分为 3 组，每组 6 头。在 FR 期间通过限制小母牛摄入自由采食量的 75%（FR75）、50%（FR50）或 25%（FR25）来进行处理，自由采食量是在 FR 前的 5d 基线期（BASE）测量的。整个研究过程中，小母牛被安置在单独的畜栏（9m2）中，喂食相同的饮食（60%饲草：40%浓缩物），可自由饮水。每日测量干物质摄入量，整个研究过程中每隔 2 分钟测量瘤胃 pH 值。在 BASE 和 FR 期的第 3 天采集瘤胃液和血液样本，并在 BASE 和 FR 期的第 5 天使用暂时隔离和冲洗的网胃技术评估短链脂肪酸（SCFA）的吸收。从 BASE 和 FR 期的第 2 天开始，使用 Cr-EDTA 脉冲剂量，然后进行 48 小时的尿液总收集，评估全肠道屏障功能。使用 SAS 的 Proc Mixed 程序分析数据，固定效应包括块、处理、时期和处理×时期的相互作用，随机效应包括块内的母牛和时期作为重复测量。在 BASE 期间，处理之间的干物质摄入量没有差异，但根据实验模型，FR 期间相对于 BASE 的 DMI 相当于 70%、49%和 25%，这与 75%、50%和 25%的目标值接近（处理×时期，P<0.001）。还检测到处理×时期的相互作用（P<0.001），随着 FR 严重程度的增加，瘤胃 SCFA 浓度降低，但在 BASE 期间没有差异。随着 FR 严重程度的增加，瘤胃 pH 值在 FR 期间升高，但在 BASE 期间没有差异（处理×时期，P<0.001）。随着 FR 严重程度的增加，SCFA 通过网胃的吸收倾向于减少（P=0.08）。对于单个 SCFA，乙酸盐吸收（mmol/h）FR25 和 FR50 时趋于减少（P=0.057），与 FR75 相比，FR25 和 FR50 时减少了近 70mmol/h，与 BASE（322mmol/h）相比，减少了 70mmol/h。限制到 25%（FR25）饲料的小母牛在 FR 期间的尿液 Cr 回收率高于 BASE，而 FR75 和 FR50 没有变化。本研究表明，短期 FR 的中度严重程度会降低网胃的吸收功能，但需要更严重的 FR 才能损害肉牛的全肠道屏障功能。
