A systematic review of the effects of prolonged cow–calf contact on behaviour, welfare, and productivity and A systematic review of the effects of early separation on dairy cow and calf health.

Concern from the public is growing regarding early cow-calf separation, yet proponents of this practice maintain that artificial rearing is critical for cow and calf health. Early separation is assumed to reduce the risk of transfer of pathogens from dam to the neonatal calf, but a wide range of health benefits associated with extended cow-calf contact has also been documented. The aim of the two systematic reviews discussed here was (1) to critically evaluate the scientific evidence for both acute and long-term effects of early separation versus an extended period of cow–calf contact, and (2) to report and synthesize conclusions from the literature on dairy cow and calf health in conventional rearing versus cow-calf contact systems. The reviews were published in the Journal of Dairy Science, Volume 102 of 2019, respectively page 5765 to 5783, and page 5784 to 5810. The respective titles of the reviews are: A systematic review of the effects of prolonged cow–calf contact on behaviour, welfare, and productivity and A systematic review of the effects of early separation on dairy cow and calf health. 

In the studies, primary research papers were found through targeted Web of Science searches, the reference lists of recent reviews for each topic, and the reference lists of papers identified from these sources. Studies were included if they were published in English, the full text was accessible, and they compared treatments with and without contact between dairy cows and calves for a specified period. The resulting manuscripts underwent a 4-step appraisal process, and further manuscripts were sourced from reference lists. The outcomes investigated were the behaviour, welfare (excluding physical health), and performance (milk yield and growth, respectively) of dairy cows and calves. Sufficient literature was also available to assess mastitis in cows, and scours, cryptosporidiosis, Johne’s disease, pneumonia, immunity and mortality in calves. 

Early separation (within 24 h postpartum) was found to reduce acute distress responses of cows and calves. However, longer cow–calf contact typically had positive longer-term effects on calves, promoting more normal social behaviour, reducing abnormal behaviour, and sometimes reducing responses to stressors. In terms of productivity, allowing cows to nurse calves generally decreased the volume of milk available for sale during the nursing period, but the authors found no consistent evidence of reduced milk production over a longer period. A prolonged period of nursing increased calf weight gains during the milk-feeding period. In summary, extended cow–calf contact aggravates the acute distress responses and reduces the amount of saleable milk while the calves are suckling, but it can have positive effects on behaviours relevant to welfare in the longer term and benefit calf growth. The strength of these conclusions is limited, however, given that relatively few studies address most of these effects and that experimental design including timing of contact and observations are often inconsistent across studies. Few studies presented indicators of long-term welfare effects other than abnormal and social behaviour of the calves.

The results for cryptosporidiosis, pneumonia, immunity, and mortality were mixed, with some differences between studies likely attributable to flawed comparisons between cohorts. Overall, the articles addressing calf scours and mastitis pointed to beneficial or no effects of suckling. The studies addressing Johne’s disease did not find cow-calf contact to be a significant risk factor. In conclusion, the scientific peer-reviewed literature on cow and calf health provides no consistent evidence in support of early separation.