Lactations were successfully induced in 15 out of 18 non-pregnant cows treated with oestradiol-17P (0·1 mg/kg body weight) and progesterone (0·25 mg/kg body weight) on days 1-7 (where day 1 is the first day of treatment). A further 23 out of 26 cows were successfully treated with oestradiol-17 p and progesterone standardized at 40 and 100 mg/day respectively. No significant differences in milk yields were obtained by the additional treatments of twice daily milking from day 10, sustained elevation or suppression of plasma prolactin during the induction phase by reserpine and bromocryptine respectively, or by continuing oestradiol-17 p injections alone on days 8-11. Levels of plasma prolactin less than 20 ng/mI were adequate for the preparation of the mammary gland for lactation to occur. The induced lactations of 24 monozygotic twin cows ranged from 20 to 87 % of their respective siblings which had normal parturient lactations.All 11 cows treated with the standard oestrogen-progesterone treatment plus reserpine had successfully induced lactations. In the absence of oestrogen and progesterone treatment, a short period of reserpine treatment followed by dexamethasone trimethylacetate failed to induce lactation in five cows.Ninety per cent of induced cows (n = 39) and 91 % of parturient cows (n = 22) conceived and subsequently calved following natural mating.
The effects of multiple suckling by dairy heifers for short periods both before and after calving on milk production were studied. Results from heifers sucked by three calves per heifer for 1, 2, 3 and 4weeks after calving were pooled and a regression equation derived. This predicts that for each additional week that heifers are sucked in early lactation (up to 4 weeks), the post-suckling milk yield will be increased by 4.3 � 0.8% (mean � standard error) compared with similar heifers machine milked from the commencement of lactation. The sucking of heifers before calving did not enhance post-partum milk yields. However, the sucking of heifers for short periods after calving by calves that are being reared as dairy replacements offers a practical means of both increasing milk production, and possibly reducing the labour input of rearing the calves.
Oestradiol-17 p, progesterone and reserpine were utilized in three experiments in an attempt to improve the success rate and the magnitude of hormonally induced lactations. Onset of lactogenesis induced by steroid administration was measured by a surge in the lactose content of the mammary secretion and lactations were regarded as being successfully induced if milk yields exceeded 3 kg/day.In all experiments, the dose rate of oestradiol-17 p was standardized at the reduced level of 20 mg/day (approximately 0·05 mg/kg body weight daily), and progesterone maintained at 100 mg/day (approximately 0·25 mg/kg body weight daily) for the initial 7 days (days 1-7). The halving of the dose rate of oestradiol-17 p from the commonly used 0·1 mg/kg body weight daily eliminated the occurrence of noticeable physical injuries in the 60 animals so treated.Induced milk yields were not improved by either repeating the standard ovarian steroid treatment on days 16-22, extending the standard treatment for days 8-21 or continuing the steroid treatment at one-quarter the standard rate for days 8-21.Addition of reserpine to an oestradiol-17 p-progesterone treatment does improve the success rate of the hormonal induction of lactation. In experiment 1, 86% (n = 14) of heifers receiving reserpine were successfully induced into lactation compared to 45 % (n = 15) which were not.In experiments 2 and 3, 95 % (n = 19) of cows receiving both ovarian steroids and reserpine were successfully induced into lactation. However, when we consider only the milk yields of those cows sucessfully induced into lactation, reserpine (3 mg/day) administration on days 1, 6, 11, 16, 21 and 22-28, on days 22-28 alone, or on days 8, 10, 12 and 14 did not enhance induced yields.In one experiment all eleven cows failed to be induced into lactation and this was attributed to an inadequate dry period (25-43 days).
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