Pair-holding of dairy calves in outdoor calf hutches : Impact on growth and redirected suckling behaviour

Abstract: Cows are social animals but today dairy calves are generally housed in single-hutches or -pens instead of together with other calves during the first period of their lives. Concerns are that housing calves in pairs or groups increases the risk of health problems such as diarrhoea and respiratory diseases and also increases the occurrence of redirected suckling behaviours including cross-sucking. Especially cross-sucking is problematic as it can lead to injuries to the receiving calf and calves performing the behaviour can continue to perform the behaviour when older. The aim of this study was to test the effects on dairy calves (Bos taurus) of single vs. pair-housing in outdoor calf hutches on growth, general health and redirected suckling behaviour. In total 21 calves of Swedish Red and Swedish Holstein cattle were used whereof 14 calves were housed in pairs and 7 were single-housed. Both treatments were given six litres of whole milk per calf divided into two meals per day in teat-buckets. They also had access to an empty, clean teat-bucket at all hours of the day except during feeding. Calves were kept individually in calf hutches until they joined the study at day ten. Cases of diarrhoea and other diseases were recorded daily and the calves were weighed weekly. Temperature was recorded in four hour intervals. Behavioural observations were done on day 14 and then twice per week for each hutch until eight weeks of age. Recordings from behavioural observations during week 2-6 were included in the statistical analysis. Behavioural observations were made by continuous recording ten minutes before milk feeding and 20 minutes after the calves received their milk in the morning and afternoon. Non-nutritive sucking and cross-sucking were considered redirected suckling total and were grouped to test separately from only cross-sucking. Both single- and pair-housed calves were able to perform cross-sucking. All data except diarrhoea were tested for normality and homogeneity assumptions with the Shapiro-Wilk test and Bartlett’s test, respectively, and all variables were square root transformed to provide normal residuals. Not normally distributed after data transformation was tested with a non-parametric Wilcoxon rank-sum test with continuity correction. REML analysis was performed on weight and behaviour, and ANOVA was also used on weight gain. Diarrhoea was tested with a Chi2-test. Weight gain was not affected by treatment or temperature (N.S.). Pair-housed calves had more diarrhoea than single-housed calves (P<0.05). Pair-housed calves had a higher frequency of drinking milk (P<0.001) while single-housed calves licked fixtures more often than pair-housed calves before receiving milk (P<0.05). Pair-housed calves performed all registered cross-sucking both before and after receiving milk (P<0.01). There was no significant difference in redirected suckling total (non-nutritive sucking and cross-sucking) between treatments before receiving milk (N.S.), but after milk delivery pair-housed calves performed more redirected suckling total than single-housed calves (P<0.01). There were no sucking induced injuries found on any of the calves and no coughing was recorded nor any antibiotics prescribed to the calves. In conclusion, as diarrhoea and cross-sucking have negative impacts on calves’ welfare more research is needed in how to be able to house dairy calves in a way where they are able to perform social behaviours without a negative impact on welfare in terms of an increase of health issues and subjection to cross-sucking.