Fertility of norgestomet treated suckler cows.

Four studies are described involving 3050 single suckled mainly Hereford-Friesian cross beef cows treated with norgestomet and oestradiol valerate to control the ovarian cycle. In study 1 the effect of insemination timing on pregnancy rate was studied. A greater proportion of cows inseminated 48 and 72 hours after treatment became pregnant than after a single insemination at 48 hours. In study 2 large variations in fertility among farms were recorded in field trials of norgestomet and oestradiol valerate. In study 3 the effect on fertility of nutrition, weight and body condition was examined. In study 4 57.9 per cent of 1113 treated cows became pregnant to insemination at 48 and 72 hours. Cows were fed a balanced ration designed to provide for a predicted daily milk yield of 9.0 kg for a 12-week period starting six weeks before insemination. The range of fertility was from 36.7 per cent to 94.9 per cent.

Fertility of norgestomet treated dairy heifers.

Four studies are described involving 2573 Friesian heifers treated with norgestomet and oestradiol valerate to control the ovarian cycle. All treated animals were inseminated at fixed times following treatment. In study 1 insemination 48 and/or 60 hours after treatment resulted in a non-significant greater proportion of heifers becoming pregnant than at 48 X 72 hours. Large variations in fertility among farms were recorded in field trials of norgestomet (Searle) and oestradiol valerate. In study III the effect on fertility of nutrition, weight and body condition was studied. In section IV a pregnancy rate to fixed time insemination of 66-8 per cent of 500 heifers inseminated at 48 and 60 or at 48 and 72 hours after norgestomet/oestradiol valerate treatment was obtained. Heifers in study IV were fed a balanced ration designed to provide a predicted daily liveweight gain of 0-7 kg for a 12-week period starting six weeks prior to the date of insemination. The range of fertility was from 59-0 per cent to 85-7 per cent.

PIP: A total of 2630 heifers were used in 4 controlled breeding studies using norgestomet and estradiol valerate to control the ovarian cycle. In Study 1, alternative times of insemination were compared; in Study 2, the 2 most successful insemination timings in the 1st study were used in heifers throughout the United Kingdom; in Study 3, the effect of nutrition level, weight, and condition on treated heifers was considered, and in Study 4 the findings were implemented. A special polymer implant containing 6 mg norgestomet was implanted sc in the outer surface of the ear and at time of implantation a 2 ml injection of 5 mg estradiol valerate and 3 mg norgestomet dissolved in sesame oil was given im. The implant was removed after 9 days. 95% of treated heifers were in estrus within 5 days after implant removal while 71.9% of controls were in estrus over a 4-week period. 73.2% of the treated animals and 52.6% of the controls became pregnant. Insemination at 48 and 60 hours after removal produced as great a pregnancy rate as insemination at 48 and 65 or 48 and 75 hours. In field trials, this method had widely varying results depending on farm. On an average 55% became pregnant. Of those nonpregnant, running with bulls proved more effective than a 2nd artificial insemination. It was found that nutritional status played a significant role in fertility.

Early pregnancy diagnosis in cattle.

Progesterone concentrations in peripheral plasma and in milk were determined by competitive protein-binding assay each day throughout the oestrous cycle of heifers and a dairy cow and also in animals after insemination. The accuracy of detecting and forecasting pregnancy and non-pregnancy was assessed in studies involving blood-sampling of heifers on the 20th and 23rd day after artificial insemination, and milk sampling of cows on the 21st and 24th day after mating. The high degree of accuracy obtained using this procedure for an early pregnancy diagnosis would be particularly useful in herds involved in a controlled breeding programme.