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  • Title: Fertility of norgestomet treated dairy heifers.
    Author: Wishart DF, Young IM, Drew SB.
    Journal: Vet Rec; 1977 May 14; 100(20):417-20. PubMed ID: 878243.
    Abstract:
    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. 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.
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