A study was conducted to investigate the effect of group size on behavior, health, growth, welfare and innate immunity of veal calves during the finishing period. The study was carried out in spring and summer of 2012 at one commercial veal farm. Holstein-Friesian bull calves (n = 168; 44 ± 3 d of age) were assigned randomly to 1 of 3 treatments of group housing with 2, 4, or 8 calves/pen. The pens used for housing were 3 × 1.20 m (2 calves/pen), 3 × 2.40 m (4 calves/pen), and 3 × 4.80 m (8 calves/pen), supplying a total pen space allowance of 1.82 m2 /calf, regardless of pen size. Behavior was recorded from video data throughout the day from 0700 to 1900 h, during a single day each month for 5 mo using scan sampling every 5 min within 30-min observation sessions. On d 0, 1, 5, 14, 42, and 70 after grouping, continuous focal sampling around feeding time (30-min intervals before, during, and after feeding) focused on oral and aggressive behavior. Plasma cortisol, blood hemoglobin concentrations and differential leukocyte counts were determined and mRNA expression of interleukine-1β (IL-1β), IL-1 receptor antagonist (IL-1Ra), tumor necrosis factor (TNF)- α, toll-like receptor 4 (TLR4) and tachykinin 1 (TAC1) was determined using real-time RT-PCR in calves blood leukocytes. Health was evaluated monthly. Calves housed in large groups (4 or 8 calves/pen) showed more (P ≤ 0.001) conspecific contact, walking, and standing, and less (P < 0.001) manipulation of objects, self-licking, and lying when compared to calves housed in small groups (2 calves/pen). Group size had no effect on play behavior (P = 0.11) throughout the experiment. During feeding times group size had no (P ≥ 0.07) effect on any behavioral patterns except for duration of conspecific contact (P< 0.01). Aggression at feeding time was not (P > 0.23) affected by treatment. Group size treatments were similar for hip height change (P = 0.41) and heart girth change (P = 0.18) over the duration of the experiment; however, both hip height and heart girth increased (P = 0.001) with calf age. During month 1, calves in groups of 8 or 4 coughed more than calves in groups of 2, whereas calves in groups of 8 coughed more than calves in groups of 4 or 2 in month 2. Furthermore, during month 4, calves in groups of 8 had less nasal discharge than calves in groups of 2 or 4 (treatment × month, P = 0.02). Ocular discharge, ears, and fecal scores did not differ (P ≥ 0.05) among treatments. Neither plasma cortisol nor blood hemoglobin were not (P ≥ 0.37) affected by group size. 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. On the 1st month after grouping, veal calves housed in groups of 8 had greater expression of IL-1β mRNA and tended to have greater TAC1 mRNA expression than calves housed in groups of 4 and 2. In conclusion, the number of veal calves in a group when given the same space did not affect production and physiological indicators of welfare but had a transient effect on health. There is immunological evidence of stress from group housing of calves in groups of 8 when compared to those kept in groups of 4 or 2. Therefore, these data suggest that housing of veal calves in larger groups during the 5-months fattening period may lead to greater incidence of respiratory disease. |
