Short communication: Effect of age at group housing on behavior, cortisol, health, and leukocyte differential counts of neonatal bull dairy calves.

To determine the effect of age at grouping on behavior, health, and production of dairy bull calves, 90 Holstein-Friesian bull calves were housed in individual pens until moved to 1 of 3 treatments. Calves were housed in groups of 3 calves at 3 d old (GH3), 7 d old (GH7), or 14 d old (GH14) until 7 wk of age. Ten groups of 3 calves for each treatment were used, with 5 pens/treatment in each of 2 replications (10 pens/treatment, 3 treatments, 3 calves/treatment; 90 calves total). Direct behavioral observations using instantaneous scan sampling every 10 min were conducted twice per week for 7 wk. At the same times, video data were recorded for continuous observations at feeding time to observe the overall activity of group-housed calves. Hip height, heart girth, and health scores were recorded weekly and body weight was recorded at the start and end of the study. Calves in GH3 spent more time playing and but more time cross-sucking and displacing other calves from milk bottles. Calves engaged in social interaction as early as 3 d of age, and social interactions between 3 to 6 wk of age increased markedly. Calves housed in GH14 vocalized more than did calves in GH7 and GH3. No difference was found between treatments in growth performance. Calf fecal, cough, and nasal and ocular discharge scores, differential leukocyte counts, and plasma cortisol concentrations were not affected by age at grouping. However, during the first week of grouping, when calves were moved from individual pens to group pens, some calves were unable to find their milk bottles and required guidance. In conclusion, these data show no adverse effects on health or performance and some benefits on social behavior for early (d 3) grouping of calves.

Acute phase cytokines, TAC1, and toll-like receptor4 mRNA expression and health associated with group size in veal calves.

Chronic stressors are a major health and well-being issue in animals. Immune status of animals under chronic stress is compromised, thus reducing disease resistance and compromising well-being of the animal. The objective of this study was to determine the influence of group size of veal calves on immune status and leukocyte mRNA expression of acute phase cytokines, toll-like receptor 4 (TLR4) and tachykinin 1 (TAC1) over a five-month finishing period. Holstein bull calves (n=168), 44±3 days of age were assigned to one of three treatments; 2, 4, or 8 calves/pen (pen space allowance of 1.82m(2)/calf). Jugular blood samples were collected at the day of grouping and then monthly for 4 months. The differential leukocyte counts were determined and mRNA was extracted from the leukocytes. Reverse transcription-qPCR was used to measure the gene expression of interleukin-1 (IL-1ß), IL-1 receptor antagonist (IL-1Ra), tumor necrosis factor (TNF-α), TLR4, and TAC1 in leukocytes. Health was evaluated before grouping and monthly for 4 months. On the 1st month after grouping, veal calves that were housed in groups of 8 have greater expression of IL-1ß mRNA than calves housed in groups of 4 or 2 (treatment×month, P=0.04). Also at 1 month, groups of 8 had greater TAC1 expression (P<0.05) than calves housed in groups of 4 or 2. However, the expression of IL-1Ra, TNF-α, and TLR4 were not influenced by group size. In the first month of the trial, calves in groups of 8 coughed more (P<0.05) than calves in groups of 2 and coughed more than calves in groups of 4 and 2 during the 2nd month (treatment×month, P=0.03). Calves housed in groups of 8 tended to have greater neutrophil percentage (P=0.09), neutrophil to lymphocyte ratio (P=0.06), and had lower lymphocyte percentage (P=0.06) than those housed in groups of 4 or 2. In conclusion, the number of veal calves in a group, given the same space during the finishing period did not alter IL-1Ra, TNF-α, and TLR4 mRNA expression. However, housing of calves in groups of 8 was associated with greater expression of IL-1ß and TAC1 mRNA in peripheral blood leukocytes, and coughing during the first 2 months after grouping. Therefore, housing of veal calves in larger groups may lead to greater susceptibility to respiratory disease and stress.