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OPTIMISING dairy herd fertility and productivity depends on maximising the pregnancy rate (the proportion of inseminations resulting in a pregnancy). However, pregnancy rates in dairy cattle are at an all-time low in many countries, so the study by Bijker and others (2015), summarised on p 411 of this issue of Veterinary Record, makes interesting reading. The study looks at factors that influenced pregnancy rate in a 500-cow dairy herd. Using accelerometers to monitor cow activity, the authors found that insemination was most successful 11 and a half hours after the onset of increased activity. These data are reassuring, as they support the widely used AM:PM rule for insemination, where animals observed in oestrus during the morning are inseminated in the afternoon or evening, and vice versa. However, the most striking finding from the study was that an elevated milk somatic cell count (SCC) was the only significant factor in the final statistical model that affected pregnancy rate. Specifically, pregnancy rate was reduced by 10 per cent if milk SCC measured between 0 and four weeks before insemination exceeded 20,000 cells/ml. As individual cow milk SCC is measured monthly in many dairy herds to monitor subclinical mastitis, these data are readily available to farmers and veterinarians.
The study by Bijker and others …