IN the USA, it is not unusual for conception rates in dairy herds to be as low as 22 per cent and it is of concern that, in the UK, the overall conception rate is approximately 40 per cent and declining by about 1 per cent every three years. At the same time, heat detection (submission) rates are currently 50 per cent. The arguments put forward to explain this decline in fertility are, first, that yields and herd sizes have greatly increased, creating management difficulties in terms of supplying adequate nutritional energy; and, secondly, that there has been an accompanying radical change in breed structure. In 1975, the UK black and white herds were 100 per cent British Friesian in their genetic make‐up. By 1997, it was estimated that these herds contained 80 per cent North American Holstein genetics. Has there been a disregard of the heritability of fertility over the past 25 years and a reduction in heterosis? Meanwhile, the question of the optimal calving index remains to be answered. This article, part of an occasional series discussing key aspects of veterinary input into the dairy enterprise, reviews factors affecting reproductive efficiency and points to areas where effort may best be directed in terms of fertility management.
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