Comparison of production and calving data for 10 Irish dairy herds in the vicinity of an industrial chemical complex and 10 herds in rural, non-industrialised areas.

Production and calving data for 2001 to 2004 inclusive were collated for 10 dairy herds located in the vicinity of a complex of chemical industries in the Cork harbour region (target herd) and 10 herds located in rural, non-industrialised areas (control herds). The average milk yield per cow, stocking rates and culling rates were similar for the two groups of herds. The prime reasons for the disposal of animals from both groups of herds were infertility, 'old age', mastitis, lameness and low milk production, and the proportions of deaths recorded were similar. Overall, significantly more male calves were born (52 per cent), but there were no significant differences between the groups in the sex ratio, the incidence of calving difficulty or the incidence of retained placentas. A higher proportion (P<0.05) of stillbirths was observed in the control herds (5.7 per cent) than in the target herds (4.7 per cent), but there was no significant difference in perinatal mortality. There was a higher proportion of multiple births (P<0.05) in the target herds (3.93 per cent) than in the control herds (2.27 per cent). No cause-and-effect relationships between location and multiple birth rate or location and stillbirth incidence were found.