This experiment evaluated growth and reproductive development of beef heifers reared at a high stocking density and provided with access to an exercise area. The experiment was replicated over 2 yr, with a total of 180 Angus × Brahman heifers. Each year, 90 heifers were ranked by age (264 ± 1 d) and body weight (BW; 200 ± 2 kg) on d 0, and assigned to a) 1 of 6 drylot pens (10 × 14 m pens; 10 heifers/pen) resulting in a stocking density of 14 m2/heifer (DENS), or b) 1 of 3 paddocks (2-ha paddocks; 10 heifers/paddock) resulting in a stocking density of 2,000 m2/heifer (CON). On d 15, 3 DENS pens were randomly selected and given access to an exercise area (DENS-EX) for 1 h three times weekly. Negligible forage was available for CON heifers, whereas all heifers received the same limit fed diet which averaged 13 kg/heifer daily of a corn-based diet. Heifer shrunk BW was recorded after 16 h of feed and water withdrawal on d -3 and 225 for BW gain calculation. Heifer temperament (chute score, exit velocity, and temperament score) were evaluated on d 0 and 225. Heifers were also fitted on d 0 with a pedometer behind their shoulder and an ear tag (CowManager, Select Sires, Plain City, OH) to record behavioral responses. Each week, pedometer results were recorded, and blood samples were collected for puberty evaluation via plasma progesterone. Heifers from CON had more (P < 0.05) steps per 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 < 0.05) steps per week compared with DENS. Heifers from CON spent more (P < 0.05) time ruminating and eating compared with DENS and DENS-EX. No treatment effects (P ≥ 0.91) were detected for heifer BW gain (0.820, 0.815, and 0.824 kg/d for CON, DENS, and DENS-EX, respectively; SEM = 0.016). Heifers from DENS had greater (P ≤ 0.05) exit velocity and temperament score on d 225 compared with DENS-EX and CON. Heifers from DENS experienced delayed puberty attainment (treatment x day; P < 0.01) compared with DENS-EX and CON. A greater (P ≤ 0.05) proportion of CON heifers were pubertal by day 105 compared with DENS and DENS-EX (30.0, 11.6, and 15.0%, respectively; SEM = 6.5), whereas a greater (P < 0.05) proportion of CON and DENS-EX heifers were pubertal by d 154 compared with DENS (61.7, 66.7, and 43.3%, respectively; SEM = 6.5). Results from this experiment demonstrate that providing heifers with an exercise area alleviated the negative effects associated with high stocking density on their reproductive development. This work is supported by the USDA-NIFA AFRI program (#2021-67015-34083).

中文翻译：

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101 适度运动方案对高饲养密度旱地饲养的后备小母牛生殖发育的影响

该实验评估了以高饲养密度饲养并提供运动区域的小母牛的生长和生殖发育。该实验重复了两年多，总共有 180 头安格斯 × 婆罗门小母牛。每年，90 头小母牛在第 0 天按年龄（264 ± 1 天）和体重（体重；200 ± 2 kg）进行排名，并分配到 a) 6 个干燥栏中的 1 个（10 × 14 m 栏；10 头小母牛/ a) 饲养密度为 14 平方米/小母牛 (DENS)，或 b) 3 个围场中的 1 个（2 公顷围场；10 头小母牛/围场），饲养密度为 2,000 平方米/小母牛 (CON)。第 15 天，随机选择 3 个 DENS 栏，并允许每周 3 次进入锻炼区 (DENS-EX)，每次 1 小时。CON 的小母牛可获得的草料可以忽略不计，而所有小母牛都接受相同的限制饲喂饮食，即每只小母牛每天平均 13 公斤玉米为主的饮食。在第-3天和第225天停料16小时后记录小母牛收缩的体重，以计算体重增加。在第 0 天和第 225 天评估小母牛气质（溜槽分数、退出速度和气质分数）。还在第 0 天为小母牛安装计步器和耳标（CowManager，Select Sires，Plain City，OH），以记录行为反应。每周记录计步器结果，并收集血样通过血浆黄体酮进行青春期评估。与 DENS 和 DENS-EX 相比，来自 CON 的小母牛每周步数更多 (P < 0.05)（分别为 23,973、6,706 和 12,354 步/周；SEM = 1,247），而 DENS-EX 小母牛每周步数更多 (P < 0.05)。与 DENS 相比，每周减少 0.05) 步。与 DENS 和 DENS-EX 相比，来自 CON 的小母牛花费更多（P < 0.05）时间进行反刍和进食。对于小母牛体重增加，没有检测到治疗效果（P ≥ 0.91）（CON、DENS 和 DENS-EX 分别为 0.820、0.815 和 0.824 kg/d；SEM = 0.016）。与 DENS-EX 和 CON 相比，来自 DENS 的小母牛在第 225 天具有更高的退出速度和性情得分 (P ≤ 0.05)。与 DENS-EX 和 CON 相比，来自 DENS 的小母牛青春期达到延迟（治疗 x 天；P < 0.01）。与 DENS 和 DENS-EX 相比，第 105 天时 CON 的小母牛进入青春期的比例更高（P ≤ 0.05）（分别为 30.0、11.6 和 15.0%；SEM = 6.5），而与 DENS 相比，CON 和 DENS-EX 小母牛在第 154 天时已进入青春期（分别为 61.7%、66.7% 和 43.3%；SEM = 6.5）。该实验的结果表明，为小母牛提供运动区域减轻了高饲养密度对其生殖发育的负面影响。这项工作得到了 USDA-NIFA AFRI 计划 (#2021-67015-34083) 的支持。