PASSIVE-IMMUNIZATION OF NEWBORN DAIRY CALVES ON 3 FARMS WITH DIFFERENT HOUSING SYSTEMS

Three groups, each consisting of 21 cow-calf pairs, from three differe nt farms were used to study the effect of housing system at calving on the transfer of passive immunity from mother to young. Natural suckli ng was permitted on all the farms. Farms A and B were part of the same Agricultural Research Station while farm C was a commercial dairy uni t. On farm A the cow was tethered in an individual box at calving, on farm B individual loose pens were used, while on farm C the calving co ws were kept loose in a large group pen. Behaviour was recorded from t he beginning of calving to the first suckling. On all farms, calves we re removed from the mother when 24 hours old, except for those calves which did not suckle within 12 hours after birth. The non-sucklers wer e removed at 12 hours, kept in individual pens and fed colostrum by ha nd. Blood samples were taken from all calves 36 hours after birth, and the plasma IgG concentrations were determined. On farm A 17/21 calves suckled within 12 hours after birth. The number of sucklers on farm B was 19/21 and on farm C 16/21. At 36 hours of age, significant differ ences in the plasma IgG levels were observed between the different gro ups of calves (including only calves that suckled). Calves on farm B ( individual loose pens) showed the highest levels of plasma IgG, wherea s those housed in the group pen on farm C had the lowest values. Calve s on farm A had intermediate levels. On farm C, only one calf suckled exclusively its mother and four suckled only alien cow(s). Eleven of t he calves born into the group housing suckled both their mothers and a lien cows. The low average plasma IgG levels observed for the calves o n farm C calves were attributed to their extensive suckling of non-mot her cows. Among the calves that suckled only their mothers, there was a significant effect of time on 36 h plasma IgG. The calves that suckl ed early achieved the highest 36-hour plasma IgG levels.