This experiment evaluated growth, physiological responses, and puberty attainment in beef heifers reared in drylots with a high stocking density, and provided or not with a moderate exercise regimen. A total of 180 heifers (75% Angus × 25% Brahman) were used in this experiment replicated over 2 yr. Each year, 90 heifers were ranked by age (264 ± 1 d) and body weight (BW on d -3; 200 ± 2 kg) on d 0, and assigned to a) 1 of 6 drylot pens (10 × 14 m pens; 10 heifers/pen) with a stocking density of 14 m2/heifer (DENS), or b) 1 of 3 pastures (2-ha pastures; 10 heifers/pasture) with a stocking density of 2,000 m2/heifer (CON). Beginning on d 15, 3 DENS pens were given access to an exercise area (DENS-EX) 3 times/week (1 h). Negligible forage was available for CON, whereas heifers from all treatments received the same limit-fed diet (~13 kg/heifer daily). Shrunk BW was recorded after 16 h of feed and water withdrawal on days -3 and 225 to calculate BW gain. Temperament was evaluated on d 0, 128, and 224. Heifers were fitted with a pedometer behind their shoulder on d 0 to record physical activity. Pedometer results and blood samples were collected weekly for progesterone analysis. Hair samples from the tail switch were collected every 28 d. Data were analyzed with pen or pasture as experimental unit, via ANOVA using the MIXED or GLIMMIX procedures of SAS (SAS Inst. Inc., Cary, NC). Heifers from CON had more (P < 0.01) steps/week compared with DENS and DENS-EX (23,973, 6,706, and 12,354 steps/week, respectively; SEM = 1,247), and DENS-EX heifers had more (P < 0.01) steps per week compared with DENS. No treatment effects (P ≥ 0.91) were detected for heifer BW gain (~0.820 kg/d). Hair cortisol concentrations were greater (P ≤ 0.05) in DENS and DENS-EX compared with CON beginning on d 56. Exit velocity and temperament score were greater (P ≤ 0.05) in DENS compared with DENS-EX and CON on d 224. Puberty attainment was delayed (treatment x day; P < 0.01) in DENS compared with DENS-EX and CON. A greater (P ≤ 0.05) proportion of CON were pubertal by d 105 compared with DENS and DENS-EX (30.0, 11.6, and 15.0%, respectively; SEM = 6.5), while a greater (P < 0.05) proportion of CON and DENS-EX were pubertal by d 154 compared to DENS (61.7, 66.7, and 43.3%, respectively; SEM = 6.5). Rearing replacement heifers in drylots with high stocking density has detrimental effects to their puberty attainment, and the moderate exercise regimen partially alleviated this negative outcome.

中文翻译：

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适度运动方案对高饲养密度旱地饲养肉牛发育和青春期达到的影响


该实验评估了在高放养密度的旱地饲养的小母牛的生长、生理反应和青春期的实现，并提供或不提供适度的运动方案。该实验总共使用了 180 头小母牛（75% 安格斯 × 25% 婆罗门），重复了 2 年。每年，90头小母牛根据年龄（264±1天）和体重（第-3天的体重；200±2公斤）在第0天进行排名，并分配到a）6个干燥栏中的1个（10×14m栏） ； 10 头小母牛/栏），饲养密度为 14 平方米/小母牛（DENS），或 b) 3 个牧场中的 1 个（2 公顷牧场；10 头小母牛/牧场），饲养密度为 2,000 平方米/小母牛（CON）。从第 15 天开始，让 3 个 DENS 栏进入锻炼区 (DENS-EX)，每周 3 次（1 小时）。 CON 的可用草料可以忽略不计，而所有处理的小母牛都接受相同的限制饲喂饮食（每头小母牛每天约 13 公斤）。在第-3天和第225天停食16小时和停水后记录缩小的体重，以计算体重增加。在第 0、128 和 224 天评估气质。在第 0 天，小母牛在肩后安装计步器以记录身体活动。每周收集计步器结果和血样用于黄体酮分析。每 28 天采集一次尾部毛发样本。使用 SAS（SAS Inst. Inc.，卡里，北卡罗来纳州）的 MIXED 或 GLIMMIX 程序，以围栏或牧场作为实验单位，通过方差分析对数据进行分析。与 DENS 和 DENS-EX 相比（分别为每周 23,973、6,706 和 12,354 步；SEM = 1,247），来自 CON 的小母牛每周步数更多 (P < 0.01)，而 DENS-EX 的小母牛则更多 (P <)与 DENS 相比，每周减少 0.01) 步。对于小母牛体重增加（~0.820 kg/d）没有检测到治疗效果（P ≥ 0.91）。头发皮质醇浓度更高（P ≤ 0.05) 与第 56 天开始的 CON 相比，在 DENS 和 DENS-EX 中。与第 224 天的 DENS-EX 和 CON 相比，DENS 中的退出速度和气质得分更大 (P ≤ 0.05)。青春期达到延迟（治疗 x 天；与 DENS-EX 和 CON 相比，DENS 中的 P < 0.01)。与 DENS 和 DENS-EX 相比，第 105 天时青春期的 CON 比例更高（P ≤ 0.05）（分别为 30.0、11.6 和 15.0%；SEM = 6.5），而 CON 比例更高（P < 0.05）与 DENS 相比，DENS-EX 和 DENS-EX 在 154 天时已进入青春期（分别为 61.7%、66.7% 和 43.3%；SEM = 6.5）。在高饲养密度的旱地饲养后备小母牛对其青春期的实现产生不利影响，而适度的运动方案部分缓解了这种负面结果。