aGENO Breeding and A.I. Association, Post Box 4123, N-2300 Hamar, Norway bTINE Norwegian Dairies BA, Post Box 9051, Grønland, N-0133 Oslo, Norway cSection of Preventive Veterinary Medicine, Department of Large Animal Clinical Sciences, The Norwegian School of Veterinary Sciences, Post Box 8146, Dep., N-0033 Oslo, Norway dDepartment of Population Medicine, Ontario Veterinary College, University of Guelph, Guelph, Ont., Canada N1G 2W1 eSection of Food Hygiene, Department of Pharmacology, Microbiology and Food Hygiene, The Norwegian School of Veterinary Science, Post Box 8146, Dep., N-0033 Oslo, Norway
Dairy herds in Møre and Romsdal County, Norway (regarded as initially free from the bovine virus diarrhoea virus (BVDV) infection) were studied retrospectively from 1992 to 1996. The herd reproductive performance (time to first calving, calving interval, and number of breeding services) was investigated for a potential effect of BVDV sero-conversion. The herd culling pattern — possibly affecting the above measurements — was included for investigation. Two different statistical models were used: the generalised estimating equation (GEE) method and multilevel modelling using Gibbs sampling.
Though slightly different estimates resulted, both models agreed on an effect of BVDV in the second year after sero-conversion on the herd average time to first calving by — on an average — 14–16 days. In subsets of case herds testing positive for BVDV antibodies among young stock, the impact on time to first calving tended to be more pronounced by an additional increase of 18 days. No effect on the number of breeding services for heifers or cows was observed (indicating a need to search for other determinants than reduced conception risk). There appeared to be no effect of BVDV on the herd average calving interval.
There was a tendency for a higher risk for reporting animals lost/died in sero-converted herds, which we believe might be related to the occurrence of mucosal disease.
This article was published in Preventive Veterinary Medicine, 51, Paul S. Vallea,b,c, S. Wayne Martind and Eystein Skjervee, Time to first calving and calving interval in bovine virus diarrhoea virus (BVDV) sero-converted dairy herds in Norway, 17-36, Copyright Elsevier 2001.