1Oregon State University - Eastern Oregon Agricultural Research Center,Burns,OR 97720,USA.
Animal. 2017 Dec;11(12):2260-2267. doi: 10.1017/S1751731117001070. Epub 2017 May 19.
In all, 60 Angus×Hereford heifers were ranked by age and BW (210±2 days and 220±2 kg) on day 0, and assigned to: (a) one of three drylot pens (10×14 m pens; 10 heifers/pen) resulting in a stocking density of 14 m2/heifer (HIDENS; n=3), or (b) one of three pastures (25 ha pastures; 10 heifers/pasture), resulting in a stocking density of 25 000 m2/heifer (LOWDENS; n=3). Pastures were harvested for hay before the beginning of this experiment, and negligible forage was available for grazing to LOWDENS heifers during the experiment (days 0 to 182). All heifers received the same limited-fed diet, which averaged (dry matter basis) 4.0 kg/heifer daily of hay and 3.0 kg/heifer daily of a corn-based concentrate. Heifer shrunk BW was recorded after 16 h of feed and water withdrawal on days -3 and 183 for BW gain calculation. On day 0, heifers were fitted with a pedometer behind their right shoulder. Each week, pedometer results were recorded and blood samples were collected for puberty evaluation via plasma progesterone. Plasma samples collected on days 0, 28, 56, 84, 112, 140, 161 and 182 were also analyzed for cortisol concentrations. On days 0, 49, 98, 147 and 182, hair samples were collected from the tail switch for analysis of hair cortisol concentrations. On days 28, 102 and 175, blood samples were collected for whole blood RNA isolation and analysis of heat shock protein (HSP) 70 and HSP72 mRNA expression. Heifers from LOWDENS had more (P<0.01) steps/week compared with HIDENS. No treatment effects were detected (P=0.82) for heifer BW gain. Plasma cortisol concentrations were greater (P⩽0.05) in LOWDENS compared with HIDENS heifers on days 84, 140, 161 and 182 (treatment×day interaction; P<0.01). Hair cortisol concentrations were greater (P<0.01) in HIDENS compared with LOWDENS heifers beginning on day 98 (treatment×day interaction; P<0.01). Heifers from LOWDENS had greater (P=0.04) mean mRNA expression of HSP72, and tended (P=0.09) to have greater mean mRNA expression of HSP70 compared with HIDENS. Heifers from HIDENS experienced delayed puberty attainment and had less (P<0.01) proportion of pubertal heifers on day 182 compared with LOWDENS (treatment×day interaction; P<0.01). In summary, HIDENS altered heifer stress-related and physiological responses, and delayed puberty attainment compared with LOWDENS.
总共有 60 头安格斯×赫里福德小母牛根据年龄和 BW（210±2 天和 220±2 公斤）在第 0 天进行排名，并分配到：（a）三个干草场之一（10×14 米的畜栏；每栏 10 头小母牛），导致每头小母牛的饲养密度为 14 平方米/头（HIDENS；n=3），或（b）三个牧场之一（25 公顷牧场；每头小母牛/牧场），导致每头小母牛的饲养密度为 25 000 平方米/头（LOWDENS；n=3）。在这个实验开始之前，牧场就已经收割了干草，而 LOWDENS 小母牛在实验期间（第 0 天到 182 天）几乎没有可用的牧草供放牧。所有的小母牛都接受了相同的限量喂养的饮食，平均每天每头小母牛有 4.0 公斤干草和 3.0 公斤玉米基浓缩饲料。在第-3 天和 183 天，在 16 小时的禁食和禁水后，记录小母牛的收缩 BW，以计算 BW 增益。在第 0 天，在小母牛的右肩后面安装了计步器。每周记录计步器的结果，并采集血液样本，通过血浆孕酮评估青春期。还分析了第 0、28、56、84、112、140、161 和 182 天采集的血浆样本中的皮质醇浓度。在第 0、49、98、147 和 182 天，从小母牛的尾巴上采集毛发样本，用于分析毛发皮质醇浓度。在第 28、102 和 175 天，采集血液样本用于分离全血 RNA，并分析热休克蛋白（HSP）70 和 HSP72 mRNA 表达。与 HIDENS 相比，LOWDENS 的小母牛每周的步数更多（P<0.01）。未检测到处理对 BW 增益的影响（P=0.82）。与 HIDENS 相比，LOWDENS 的小母牛在第 84、140、161 和 182 天（处理×天交互作用；P<0.01）的血浆皮质醇浓度更高。从第 98 天开始，HIDENS 的小母牛的毛发皮质醇浓度高于 LOWDENS（处理×天交互作用；P<0.01）。与 HIDENS 相比，LOWDENS 的小母牛 HSP72 的平均 mRNA 表达更高（P<0.01），而 HSP70 的平均 mRNA 表达有增加的趋势（P=0.09）。与 HIDENS 相比，LOWDENS 的小母牛的青春期获得时间更早，第 182 天的青春期小母牛比例更高（处理×天交互作用；P<0.01）。总之，与 LOWDENS 相比，HIDENS 改变了小母牛的应激相关和生理反应，并延迟了青春期的获得。
