The control of ovarian activity in the cow using orally active 6-methyl-17-acetoxyprogesterone ( MAP).

Abstract

THE CONTROL OF OVARIAN ACTIVITY IN THE COW USING ORALLY ACTIVE 6 -METHYL - 17 ACETOXYPROGESTERONE (MAP) E. M. ROBERTS*, B. J. DOYLE and B. M. BINDON I. INTRODUCTION Synchronization of oestrus in cattle would have a great practical advantage in artificial insemination. Hansel and Malven (1960) reported suppression of oestrous cycles following the feeding of 6-methyl-17-acetoxyprogesterone (MAP) $ to Friesian heifers. Hansel ( 1961) reviewed subsequent work using oral progestogens and concluded that the minimum period of feeding for effective synchronization of oestrus was 15 days with a minimum dose rate of MAP of 0.44 mg per kg of body weight (0.2 mg/lb) . Lamond ( 1962) reported the use of injected progesterone to suppress oestrus in the beef heifer, but no other work has been reported in Australia on the use of orally active progestogens for control of oestrus and ovulation in the cow. Because of the greater control over feeding and more simple observation of oestrus in dairy than in beef cattle, a series of trials was conducted to investigate the efficacy of MAP in synchronizing oestrus and ovulation in a group of cows. The level of fertility following mating or insemination at the first oestrus after treatment was also determined. II. MATERIALS AND METHODS Three trials were conducted: (a) Trial 1, at Penrith, 40 miles west of Sydney. Ten lactating Australian Illawarra Shorthorn cows of (455 kg) mean body weight were individually fed 165 mg mixed with a concentrated dairy meal. The total intake 15 days was 330 mg per cow. All cows were observed for equal numbers were naturally mated or inseminated. Returns to service and calving dates were noted. approximately 1000 lb of MAP, twice daily, of MAP per day for oestrus twice daily and *School of Wool Technology, The University of New South Wales. tN.S.W. Milk Board, Artificial Stock Breeding Centre, Graham Park, Berry. $School of Wool Technology, The University of New South Wales. Present Address: C.S.I.R.O. Division of Animal Physiology, St. Lucia, Brisbane. !$Provera-The Upjohn Company. 40 (b) Trial 2 at Aberdeen, N.S.W. To provide heifers in oestrus for test mating of bulls, 42 virgin dairy heifers of mixed breed and approximately 5.00 lb (227 kg) liveweight, were group fed 2 lb (0.9 kg) of dairy meal daily in open troughs for a period of 15 days. Each 2 lb of meal contained 150 mg of MAP. Pre-feeding of untreated dairy meal for 2-4 days was suficient to accustom all cows to the routine necessary to ensure a reasonably equal intake of the progestogen-meal mixture. Twenty one pairs of heifers were each mated naturally to a different bull from a group of 21 stationed on the N.S.W. Milk Board' Artificial Stock Breeding s Centre at Aberdeen. Heifers not in oestrus within 120 hr of the end of treatment were given oestrogen to induce oestrus; but these were not identified. All heifers were observed subsequently for recurrence of oestrus; pregnancy was confirmed by rectal examination and slaughter. (c) Trial 3 at Aberdeen, N.S.W. Trial 3 was essentially a replicate of Trial 2; 15 non-pregnant dairy heifers of mixed breed were used. III. RESULTS AND DISCUSSION (a) Oestrus The incidence of oestrus after treatment was similar in each trial (Table 1). Sixty eight '/o of all animals exhibited oestrus between 48 and 72 hr; most of the remainder came into oestrus during the following 48 hr. It appears therefore that MAP fed daily at the rate of 0.66 mg/kg (0.3 mg/lb), was effective in the synchronization of oestrus. TABLE 1 Oestrus patterns for all cows and heifers fed MAP (b) Conception In Trial 1, 5 of the 10 cows conceived. In Trial 2, 21 of the 42 heifers became pregnant; this proportion may have been higher had not some heifers been 41 treated with oestrogen. Four, or possibly five, of the 11 heifers untreated with oestrogen in Trial 3 were pregnant six weeks after mating. Thus fertility at the first oestrus after treatment was lower than normal. It remains to be determined whether fertility would be higher at subsequent oestrous periods. (c) Normality of oestrus. In Trials 2 and 3 oestrus was not completely normal since successful service could not be accomplished in some heifers unless they were tethered. IV. ACKNOWLEDGMENTS The authors wish to thank the following for assistance in the trials : -Upjohn Pty. Ltd. for the supply of MAP (Provera) ; the Prisons and the staff of the dairy at the Emu Plains Training Farm; Veterinarian of the N.S.W. Department of Agriculture; Mr. B. W. Veterinary Officer, Newcastle and Mr. M. Leake, N.S.W. Milk Stock Breeding Centre, Aberdeen, N.S.W. V. REFERENCES H ANSEL conduct of these Comptroller of Mr. H. Beattie, Bootes, District Board Artificial , W. ( 1961) . Oestrous cycle and ovulation control in cattle. Journal Dairy Science 44: 2307. H , W. and M ALVERN , P. V. ( 1960 ) . Oestrous cycle regulation in beef cattle by orally active progestational agents. Journal Animal Science 19: 1324. L AMOND , D. ( 1962). Synchronization of oestrus and ovulation in beef heifers. Proceedings ANSE L of the Australian Society of Animal Production 4: 72. 42