Prairie Research Unit, Mississippi State University, Prairie, MS 39756, USA.
Department of Animal Science, Texas A&M University, College Station, TX 77843, USA.
J Anim Sci. 2024 Jan 3;102. doi: 10.1093/jas/skae150.
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 day -3; 200 ± 2 kg) on day 0, and assigned to a) one of six drylot pens (10 × 14 m pens; 10 heifers per pen) with a stocking density of 14 m2/heifer (DENS), or b) one of three pastures (2-ha pastures; 10 heifers per pasture) with a stocking density of 2,000 m2/heifer (CON). Beginning on day 15, three DENS pens were given access to an exercise area (DENS-EX) 3 times/wk (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 days 0, 128, and 224. Heifers were fitted with a pedometer behind their shoulder on day 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 an 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 per week compared with DENS and DENS-EX (23,973, 6,706, and 12,354 steps/wk, 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 day 56. Exit velocity and temperament score were greater (P ≤ 0.05) in DENS compared with DENS-EX and CON on day 224. Puberty attainment was delayed (treatment × day; P < 0.01) in DENS compared with DENS-EX and CON. A greater (P ≤ 0.05) proportion of CON were pubertal by day 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 day 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 on their puberty attainment, and the moderate exercise regimen partially alleviated this negative outcome.
本实验评估了在高饲养密度的干栏中饲养的肉牛小母牛的生长、生理反应和青春期获得情况，并提供或不提供适度的运动方案。共有 180 头小母牛（75%安格斯×25%婆罗门）参与了这项实验，在两年内进行了重复。每年，90 头小母牛按年龄（264±1 d）和体重（-3 天的 BW；200±2 kg）进行排名，并分配给 a）六个干栏中的一个（10×14 m 栏；每个栏 10 头小母牛），饲养密度为 14 m2/小母牛（DENS），或 b）三个牧场中的一个（2 公顷的牧场；每个牧场 10 头小母牛），饲养密度为 2,000 m2/小母牛（CON）。从第 15 天开始，三个 DENS 围栏每天有 3 次机会进入运动区（DENS-EX）（每次 1 小时）。CON 几乎没有可用的饲料，而所有处理组的小母牛都接受相同的限量喂养饮食（每天约 13 公斤/小母牛）。在第-3 天和第 225 天，在停止采食和饮水 16 小时后记录收缩 BW，以计算 BW 增益。在第 0、128 和 224 天评估小母牛的性情。在第 0 天，在小母牛的肩部后面安装计步器以记录身体活动。每周收集计步器结果和血液样本进行孕激素分析。每隔 28 天从尾巴切换处采集头发样本。使用 SAS（SAS Inst. Inc.，Cary，NC）的 MIXED 或 GLIMMIX 过程以围栏或牧场作为实验单位，通过 ANOVA 分析数据。与 DENS 和 DENS-EX 相比，CON 组的小母牛每周的步数更多（P<0.01；分别为 23,973、6,706 和 12,354 步/周；SEM=1,247），而 DENS-EX 组的小母牛每周的步数更多（P<0.01）。处理（P≥0.91）对 BW 增益没有影响（小母牛的 BW 增益约为 0.820 公斤/天）。从第 56 天开始，与 CON 相比，DENS 和 DENS-EX 中的小母牛的皮质醇浓度更高（P≤0.05）。与 CON 和 DENS-EX 相比，DENS 中的小母牛的出口速度和性情评分更高（P≤0.05；在第 224 天）。与 DENS-EX 和 CON 相比，DENS 中小母牛的青春期获得时间延迟（处理×天；P<0.01）。与 DENS 和 DENS-EX 相比，CON 中有更大比例（P≤0.05）的小母牛在第 105 天达到青春期（分别为 30.0%、11.6%和 15.0%；SEM=6.5），而 CON 和 DENS-EX 中有更大比例（P<0.05）的小母牛在第 154 天达到青春期（分别为 61.7%、66.7%和 43.3%；SEM=6.5）。在高饲养密度的干栏中饲养后备小母牛会对其青春期获得产生不利影响，适度的运动方案部分缓解了这种负面影响。
