Separation of calves from cows within hours or days of birth is common on dairy farms. Stakeholders have conflicting perspectives on whether this practice is harmful or beneficial for the animals' welfare and production. Our objective was to critically evaluate the scientific evidence for both acute and long-term effects of early separation versus an extended period of cow-calf contact. The outcomes investigated were the behavior, welfare (excluding physical health), and performance (milk yield and growth, respectively) of dairy cows and calves. 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. 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 behavior, reducing abnormal behavior, 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 we found no consistent evidence of reduced milk production over a longer period. Allowing 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 behaviors 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 behavior of the calves.

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 neonatal calf, but a wide range of health benefits associated with extended cow-calf contact has also been documented. The aim of this systematic review was to report and synthesize conclusions from the literature on dairy cow and calf health in conventional rearing versus cow-calf contact systems. Peer-reviewed, published manuscripts, written in English, directly comparing dairy cow or calf health in artificial versus suckling systems, were eligible for inclusion. We conducted 7 targeted searches using Web of Science to identify key literature on important health conditions. The resulting manuscripts underwent a 4-step appraisal process, and further manuscripts were sourced from reference lists. This process resulted in a final sample of 70 articles that addressed cow and calf health. Sufficient literature was available to assess mastitis in cows, and scours, cryptosporidiosis, Johne's disease, pneumonia, immunity, and mortality in 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.

Longitudinal infection data on Mycobacterium avium subspecies paratuberculosis (MAP) was collected on three dairy farms in Northeastern United States during approximately 10 years. Precise data on animal characteristics and animal location within farm were collected on these farms. Cows were followed over time with regard to MAP status during biannual fecal and serum sampling and quarterly serum sampling. Approximately 13 000 serum samples, 6500 fecal samples and 2000 tissue samples were collected during these years. Prevalence of positive samples was 1.4% for serological samples, 2.2% in fecal samples and 16.7% in tissue samples. Infection dynamics of MAP was studied and resulted in a number of potential changes in our understanding of MAP infection dynamics. First, a high prevalence of MAP infection was observed in these herds due to lifetime follow up of cows, including slaughter. Second, two distinctly different infection patterns were observed, so called non-progressors and progressors. Non-progressors were characterized by intermittent and low shedding of MAP bacteria and a virtual absence of a humoral immune response. Progressors were characterized by continuous and progressive shedding and a clearly detectable and progressive humoral immune response. Strain typing of MAP isolates on the three farms identified on two of three farms a dominant strain type, indicating that some strains are more successful in terms of transmission and infection progression. Continuous high quality longitudinal data collection turned out to be an essential tool in our understanding of pathobiology and epidemiology of MAP infections in dairy herds.

a b s t r a c tDairy calves are often separated from the cow soon after birth and prevented from nursing, but little is known about the effects of nursing on the development of the cow-calf bond. This study evaluated the effect of nursing on affiliative behaviours between the dam and her calf including allogrooming, proximity and latency to reunite after a period of separation. Holstein cow-calf pairs were randomly allocated to three treatments differing only in nutritional dependency on the dam: milk feeder (n = 10 pairs), combined (n = 10 pairs) or nursing (n = 10 pairs). Milk feeder calves could feed ad libitum from an automated milk-feeder, combined calves could suckle from their dams at night and could feed ad libitum from an automated milk feeder and nursing calves could suckle from their dams at night. Cows and calves were kept together during the night (between 20:00 h and 08:00 h) and were housed adjacent to each other during the day (between 08:00 h and 20:00 h). Direct live observations were performed 2 h following the opening of the gate that allowed calves to mix with cows at night. All pairs spent more time (% of observations) allogrooming each other (i.e. own cow/calf) than they did grooming other cows and calves within the same group (10 ± 0.8% vs. 0.4 ± 0.7%, t 29 = 168.8, P < 0.001). The time cow-calf pairs spent allogrooming did not vary with treatment; 10.0 ± 0.8%, F 2, 27 = 0.4, P = 0.696). Similarly, time spent in close proximity without nursing did not differ among treatments; 31 ± 2.6%, F 2, 27 = 0.6, P = 0.543). The percentage of occasions a pair did not reunite (i.e. not observed within 1 m of each other within 3 min) was 23% for the milk feeder pairs, 38% for the combined pairs and 32% for the nursing pairs ( 2 = 3.9, P = 0.415). Nevertheless suckling from another cow than own dam was observed at least once by 19 of the 20 calves that were allowed to suckle. Latency to reunite (among pairs that did so within 180 s) was highest for the combined pairs and tended to be lower for milk feeder and nursing calves; 52.5 ± 16.0, 23.3 ± 8.3 and 12.9 ± 5.8; F 2, 24 = 3.1, P = 0.062). These results indicate that dam and calf form a bond independent of nursing.

Many contemporary dairy cattle housing practices are at odds with societal perceptions of positive animal welfare. The public (i.e., those external to the dairy industry) typically emphasizes the importance of naturalness for dairy cattle, such as through provision of pasture, freedom of movement, and the ability to interact socially with conspecifics. Yet, in the United States, the majority of lactating dairy cattle are reportedly housed without any access to pasture, and almost 39% of dairy farms use tiestalls, which restrict movement and social interactions. In addition to being in conflict with public expectations, a lack of pasture access and restrictive housing systems are also in conflict with the animals' own motivations, which can adversely affect their welfare. For example, dairy cattle are highly motivated to access pasture and show a reduction in oral stereotypies when allowed on pasture after periods of tethering. Calves housed without social contact have cognitive deficits and exhibit increased fear responses to novelty. We argue that the long-term sustainability of the dairy industry will depend on the extent to which housing systems reflect public concerns and the animals' priorities. The adoption of technologies, such as automated feeders and remote monitoring systems, may represent a means to practically promote the animals' natural behavior while simultaneously improving individualized care. Although older generations of the public may consider technological solutions to be a further deviation from naturalness and a departure from dairy farming's agrarian roots, the definition of "naturalness" for younger generations may well have expanded to include technology. As the buying power shifts to these younger generations, the adoption of technologies that promote natural cattle behaviors may be one means toward reconciling the disconnect between public perceptions of animal welfare and contemporary dairy farming practices.