Effects of group composition on the incidence of respiratory afflictions in group-housed calves after weaning

A study consisting of 2 experiments was conducted with the aim of determining the effects of previous history of bovine respiratory disease (BRD) on animal performance and health status of transition calves housed in groups. In both experiments, calves were housed in individual hutches until weaning age at 58 d. Before weaning, BRD incidences were individually recorded on a daily basis. Following weaning, calves were moved into super hutches in groups of 8, based on their history of respiratory afflictions, and growth performance and BRD incidences were recorded for 57 d. In experiment 1, 144 female Holstein dairy calves (initial BW = 72.6 ± 1.2 kg; age = 58.5 ± 0.8 d) were distributed in 6 super hutches composed of 8 calves with no previous history of BRD (HHH), 6 super hutches composed of 6 calves without and 2 calves with a previous episode of BRD (HHR), and 6 super hutches housed 5 calves without a history of BRD and 3 calves with previous respiratory afflictions (HRR). In experiment 2, 144 Holstein female calves [58.0 ± 0.9 d; 72.5 ± 0.9 kg of body weight (BW)] were distributed in 2 treatments consisting of 9 super hutches housing integrally 8 calves with no previous BRD, and 9 super hutches housing integrally calves with a previous BRD case. The number of BRD cases after weaning progressively increased from HHH to HRR as the proportion of calves previously affected by BRD within super hutch increased, mainly due to the fact that both animals affected by BRD before weaning and those with no previous history of BRD had more relapses in HHR and HRR groups than in the HHH group. Odds of incurring BRD after grouping were 3.89 greater in calves that had a previous case of BRD than in those that did not. The average time elapsed between commingling the animals and the appearance of the first BRD case was shorter when calves that had at least one BRD episode prior to weaning were present in a group (10.8 ± 3.3 d) than when the group was formed with calves that had never experienced BRD before weaning (22.5 ± 3.3 d). Final BW (at 115 d of life) and average daily gain tended to decrease as the number of BRD cases incurred increased. In experiment 2, calves in the HHH group reached a greater BW at the end of the study than those in the RRR group and tended to have a greater average daily gain in the HHH group than in the RRR group. It is concluded that forming groups of animals with a previous BRD history should minimize the incidence of respiratory cases in those groups of calves formed by animals without a previous history of respiratory disease.