Department of Animal Science, University of California, Davis 95616.
Department of Animal and Food Sciences, Texas Tech University, Lubbock 79409.
J Dairy Sci. 2019 May;102(5):4506-4521. doi: 10.3168/jds.2018-15368. Epub 2019 Mar 7.
Many dairy calves in the southwestern regions of the United States are raised in wooden hutches with 1.23 m of free space that house 3 calves individually. Producers claim that calves in hutch systems are not ready to wean and be placed in groups at the country-average age of 6 wk. Calves may remain in this individual housing system until as late as 10 wk of age. The objective of this study was to modify space allowance of hutches and evaluate weaning readiness using age at solid feed consumption, standing behaviors, and measures of immunity. Calves were randomly assigned at 4 d of age to conventional (CONV; 1.23 m of space; n = 18), moderate (MOD; 1.85 m of space; n = 17), or maximized (MAX; 3.71 m of space; n = 19) space allowance in hutches. These modifications also changed the number of calves housed per hutch from 3 (CONV) to 2 (MOD) and 1 (MAX). Calves were fed milk replacer via bottle twice daily until weaning and offered ad libitum feed throughout the experiment. Step-down weaning was initiated (Wi) at age 53 or 54 d by withdrawal of the p.m. bottle and was completed (Wc) 11 d later by removal of the a.m. milk replacer. Accelerometer data for standing behaviors were collected relative to Wi (3 consecutive days to represent -4 wk, -3 d, 3 d, and 3 and 5 wk). Blood samples were collected in the a.m. just before Wi (d 0) and at d 3, 11, 14, and 18 after Wi. Calves provided with more space (MOD and MAX) compared with CONV calves consumed feed at an earlier age and had slightly healthier erythrocytes, greater circulating glucose, and fewer circulating eosinophils. The CONV calves had haptoglobin (Hp) responses to the stressors of both Wi and Wc and had more IFN-γ from whole blood stimulated with phytohemagglutinin-P. The MAX calves had the least active neutrophils (phagocytosis and oxidative burst), but MOD calves' leukocytes secreted the most TNF-α from whole blood stimulated with lipopolysaccharide. Just before and after weaning, MAX calves spent more time per day in the standing position than CONV and MOD calves and had an Hp response to Wc, but MOD calves did not have an Hp response to Wi or Wc. Based on these results, MOD calves were the most ready for weaning; therefore, they potentially can be moved to group housing at an earlier age than CONV calves, thus improving animal welfare concerns over space allowance and individual housing.
许多美国西南部地区的奶牛犊都在有 1.23 米自由空间的木制畜栏中饲养，每个畜栏可单独容纳 3 头奶牛犊。生产者声称，畜栏系统中的奶牛犊还没有准备好断奶并在 6 周龄时被放入群体中。奶牛犊可能会在这种单独的饲养系统中待到 10 周龄。本研究的目的是修改畜栏的空间分配，并使用固体饲料摄入量、站立行为和免疫措施来评估断奶准备情况。奶牛犊在 4 日龄时随机分配到常规（CONV；1.23 米空间；n = 18）、适度（MOD；1.85 米空间；n = 17）或最大化（MAX；3.71 米空间；n = 19）空间分配的畜栏中。这些修改还将每个畜栏的奶牛犊数量从 3 头（CONV）改为 2 头（MOD）和 1 头（MAX）。奶牛犊每天通过奶瓶接受两次牛奶代用品喂养，直到断奶，并在整个实验过程中提供自由采食的饲料。在 53 或 54 日龄时（Wi）开始逐步断奶，通过取消下午的奶瓶喂养来进行断奶，并在 11 天后（Wc）通过去除上午的牛奶代用品来完成断奶。与 Wi（代表-4 周、-3 天、3 天和 3 周到 5 周的连续 3 天）相关的站立行为的加速计数据被收集。在 Wi 之前的早晨（d 0）和 Wi 后的第 3、11、14 和 18 天采集血液样本。与 CONV 奶牛犊相比，提供更多空间（MOD 和 MAX）的奶牛犊更早地开始进食，并具有更健康的红细胞、更高的循环葡萄糖和更少的循环嗜酸性粒细胞。CONV 奶牛犊对 Wi 和 Wc 的应激源有 haptoglobin（Hp）反应，并且在用植物血球凝集素-P 刺激的全血中产生更多的 IFN-γ。MAX 奶牛犊的中性粒细胞（吞噬作用和氧化爆发）最不活跃，但 MOD 奶牛犊的白细胞从用脂多糖刺激的全血中分泌出最多的 TNF-α。在断奶前后，MAX 奶牛犊每天在站立位置上花费的时间比 CONV 和 MOD 奶牛犊多，并且对 Wc 有 Hp 反应，但 MOD 奶牛犊对 Wi 或 Wc 没有 Hp 反应。根据这些结果，MOD 奶牛犊最适合断奶；因此，它们可以比 CONV 奶牛犊更早地转移到群体饲养中，从而改善对空间分配和单独饲养的动物福利问题的关注。
