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THE APPLICATION OF LONG- AND SHORT-TERM PROGESTAGEN TREATMENTS FOR OESTROUS CYCLE CONTROL IN HEIFERS

Summary.: Progestagen-impregnated pessaries were inserted into 205 heifers on eight farms. Treatments were either pessaries only for 20 days or pessaries for 10 days combined with an intramuscular injection of 250 mg progesterone+ 7·5 mg oestradiol benzoate on the day of insertion. Pessary retention was low (86·7%) over the 20-day period, but high (93·6%) during the 10-day period. Calving rates of heifers inseminated in oestrus following the 20-day treatment were low, while those of heifers inseminated on a fixed-time basis with the 10-day treatment were slightly higher than those of control heifers.