Relationships between milk production parameters and reproductive performance in a dairy herd using natural service

The relationship between milk production in early lactation and calving int erval (CI) was investigated in an organic dairy herd in which natural servi ce was used. Cows were loosely housed with one bull per 60 to 80 cows. 582 lactations starting between September 1996 and August 1998 were included in the analyses. A total of 495 lactations ended with a further parturition a nd 87 cows were culled more than 150 days after calving. Cows culled before 150 days of their lactation were excluded from the analyses. In addition t o the milk production parameters, the year, season of calving and parity (f irst lactation and second lactation) were included in the statistical model . Of the production parameters included in the analyses (milk kg, fat %, pr otein %, urea mg/kg and somatic cell count) only milk protein content in th e samples obtained at the first three milk sampling were negatively correla ted with the calving interval. A univariate analysis of variance revealed t hat only the protein content in the first milk sample was related significa ntly to CI. Cows culled 150 days after calving had lower milk yields and gr eater somatic cell counts than cows that remained in the herd. As the corre lation between protein content of milk and CI was weak, the conclusion was drawn that milk protein concentration is not a useful predictor of fertilit y problems in individual cows. As milk yield was not associated with the CI it is not advisible to have varying voluntary waiting periods for cows wit h different levels of milk production.