The consequences of using a sub-fertile or infertile bull is that it will take several years to restore productivity and calving patterns in a herd and will usually involve a significant increase in the involuntary culling rate, Michael McGowan of the Royal Veterinary College told the BVA meeting in Edinburgh. These consequences representd a considerable cost to the farmer, said professor McGowna. He said: "A normal, fertile bull is expected to get 90 per cent of 50 normal, cycling, disease free females pregnant within nine weeks and 60 per cent of these should be pregnant in the first three weeks of joining.
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