摘要
Improvement in the utilization of feed in livestock is an important target of breeding and nutritional programs. Recent evidence indicates a potential association between feed efficiency and fecal cortisol metabolites, which could eventually be used as an indirect assessment of this trait. This evidence is more comprehensively evaluated in here with samples for plasma cortisol (PC; ng/ml) and fecal cortisol metabolites (FCM; ng/ml) collected more often during the entire finishing phase in beef steers. Individual daily feed intake of 112 steers fed a high-moisture corn-based and haylage diet was measured over 168 d. Body weight, blood and fecal samples were collected every 14 d and ultrasound measures of backfat thickness and longissimus muscle area were taken every 28 d. Four productive performance traits were calculated: daily dry matter intake (DMI), average daily gain (ADG), feed to gain ratio (F:G) and residual feed intake (RFI). At the end of the feedlot phase, steers were ranked according to RFI and samples were analyzed for PC and FCM from the 32 steers with greatest and 32 steers with lowest feed efficiency. In addition, a sub-group of 12 steers from each of these two groups with divergent feed efficiency were subjected to hourly blood sampling for 24 h. Less efficient steers had greater DMI, F:G and consumed 1.5 kg/d more DMI (P<0.05) than steers with improved feed efficiency. No differences (P>0.10) in PC over the 12 biweekly sampling periods between steers with divergent feed efficiency were observed. However, a trend toward significance between 19:00 and 02:00 h over the hourly sampling evaluation was noticed, with the sub-group of more feed efficient steers presenting higher levels of PC in this period of the day (P=0.08). On the other hand, FCM levels displayed a distinct pattern between RFI groups over the biweekly sampling period, with more efficient cattle presenting greater levels of these metabolites (P<0.05). This study reinforces the positive association between improved feed efficiency and FCM levels over the finishing phase; and the lack of association between feed efficiency and PC when single samples are collected every two weeks through a single jugular venipuncture performed after handling the cattle for sampling. Further studies to develop sampling protocols for assessing FCM as an indicator trait for feed efficiency are warranted, as well as, studies to understand the role of endogenous glucocorticoids in the performance of the bovine.
摘要译文
提高饲料家畜的利用是育种和营养计划的一个重要目标。最近的证据表明饲料效率和粪便皮质醇代谢物之间的潜在联系，这可能最终被用作这种特质的间接评估。这方面的证据进行了更全面的评估与这里的样本血浆皮质醇（PC纳克/毫升）和粪便皮质醇代谢物（FCM;毫微克/毫升）期间牛肉肉牛整个育肥阶段收集更频繁。 112个人肉牛采食量饲喂高水分玉米为基础的饮食haylage测量超过168Ð。体重，血液和粪便样本收集的背膘厚和眼肌面积均每隔28天每14天及超声措施。计算了四个生产性能特点：每天干物质采食量（DMI），平均日增重（ADG），料重比（F：G）和残余饲料采食量（RFI）。在饲养场阶段结束，公牛是根据RFI排名和样品为PC和FCM从32公牛以最大的32公牛以最低的饲料效率进行了分析。此外，一个子组来自每个这两组具有发散饲料效率的12阉经受每小时采血24小时。低效率的公牛有更大的DMI，F：G和消耗1。为5kg / d个DMI（P10）在PC机之间的阉牛用饲料分歧效率12每两周采样周期的变化。然而，对意义和19:00在每小时采样评估02:00 h的趋势发现，与子组的多个进料有效公牛在此期间，天（P \x3d 0.08）的呈递更高水平的PC。另一方面，FCM水平显示RFI群体之间有明显的图案在两周采样期间，更高效的牛提出这些代谢产物的更高水平（P这项研究加强改善饲料效率和FCM水平在育肥阶段之间的正相关关系;而缺乏饲料效率和PC之间的关联时，单个样本通过处理牛取样后进行单一的静脉穿刺颈收集每两个星期。进一步的研究，以开发采样协议来评估流式细胞作为指示剂的特质对饲料效率是必要的，以及，研究，了解内源性糖皮质激素的在牛的性能的作用。
Y.R. Montanholi[a]; R. Palme[c]; L.S. Haas[a][1]; K.C. Swanson[b]; G. Vander Voort[a]; S.P. Miller[a]. On the relationships between glucocorticoids and feed efficiency in beef cattle[J]. Livestock Science, 2013,155(1): 130–136