Pair-housing of dairy calves in outdoor calf hutches : impact on growth and play behaviour

Sammanfattning: The aim of this study was to test the effects on dairy calves (Bos taurus) in outdoor calf hutches of individual vs. pair-housing on behaviour, growth and health. In total 33 female dairy calves of the breeds Swedish Holstein (SH) and Swedish Red (SR) cattle were used in the study. Twenty calves were pair-housed and 13 calves were individually housed. All calves had ad lib. access to water, concentrate, hay and silage and were fed three litres of whole milk twice per day with buckets equipped with a rubber teat. An extra teat bucket was always available in the calf hutch. Calves were weighed at birth and then once a week. Health protocols were filled in by the farm staff every day and collected monthly. At six, seven and eight weeks of age, calves were observed in a test arena (3.7 x 6.4 m) with a large rubber ball, five pieces of rope tied to the gates and an alien calf. Social play, locomotor play, object play, vocalisation, walk, standing together and defecate were recorded using one-zero sampling at one minute intervals for 20 minutes per session. The study began in wintertime 2017 (January 27th) and ended in early summer the same year (June 2nd). Data from the behaviour observations was analysed in SAS using a generalised linear model that tested for the effect of housing treatment, age at testing, observation period (first 10 vs. last 10 minutes in test arena) and their interactions. Diarrhoea was tested with a Chi2 -test and the relative risk to be diagnosed with diarrhoea was calculated with a Cohort. Weight gain was analysed with a t-test with the Cohran method. The behaviour observations in the test arena showed that pair-housed calves performed more social play (p<0.05) and stood more together (p<0.001) than did individually housed calves. The expression of social play increased with age (p<0.01) and occurred the most during the second observation period (min 11-20) (p<0.0001). There was no significant effect of treatment or age on locomotor play (n.s.). However, the calves performed more locomotor play during the first observation period (min 1-10) (p<0.0001). There were no significant effects on object play of treatment or period, but the calves performed more object play when six weeks old than when seven weeks (p<0.05) or eight weeks (p<0.01) old. The amount of vocalisation also decreased with age (p<0.0001), but did not differ between treatments. No significant effects were found of treatment, period or age on the number of recordings of walk. Pair-housed calves had an average daily weight gain of 0.88 kg/d and individually housed calves had average daily weight gain of 0.81 kg, but there was no significant difference in weight gain between treatments. Twelve pair-housed and five single-housed calves got diarrhoea and one pair-housed calf got an airway infection, but there were no significant differences in occurrence of diarrhoea between pair-housed and individually housed calves. In conclusion, pair-housed calves had more social behaviours in an arena test than individually housed calves. However, pair-housing as compared to individual housing of dairy calves did not significantly affect weight gain, health, locomotor play, object play or vocalisation. Further research may be needed to evaluate the effects of pair-housing on calf welfare.