The effect of an outbreak of respiratory disease on herd-level milk production of Norwegian dairy farms

This study was done to evaluate the effect of an outbreak of acute respirat ory disease associated with bovine respiratory syncytial virus (BRSV) on th e daily milk yield per cow in Norwegian dairy-cattle farms. Retrospective d ata from 184 dairy herds located in two neighbouring veterinary districts d uring the study period (December 1994-May 1995, during which an epidemic of acute respiratory disease associated with BRSV occurred in this area) were analysed. Data on the bulk-milk deliveries and the date of the outbreak we re collected at herd level, whereas information on calving dates and parity was collected at cow-level. The effect of the herd outbreaks on the daily milk yield was analysed with a repeated-measurement approach. The average d aily milk loss was estimated to be 0.70 kg per cow for 7 days after a herd outbreak (compared with the period >1 week prior to an outbreak), adjusted for the herd-level lactation stage, parity and their interaction term. We c onsider the estimated milk loss associated with a herd outbreak of epidemic respiratory disease to be of minor importance. (C) 2001 Elsevier Science B .V. All rights reserved.