Synchronization of ovulation in ewes during the breeding season was achieved by a 14 day course of progesterone injections followed by injections of pregnant mare serum gonadotrophin (PMS) and human chorionic gonadotrophin (HCG). Optimal control was attained when the PMS was given at the time of the last progesterone injection and the HCG 24 hr later. With this treatment most ovulations occurred between 20 and 28 hr after the HCG injection. However, none of the ewes exhibited oestrus at this time. Greater variability in the time of ovulation was found when the progesterone-PMS and PMS-HCG intervals were 0 hr and 48 hr, or 24 hr and 24 hr, and with these treatments about 80 per cent. of the ewes exhibited oestrus just before ovulation. On the 0-48 hr treatment schedule with artificial insemination 3-7½ hr after the HCG injection, 13 of 22 ewes had fertilized eggs or embryos when killed 3 or 35 days later.
Each year, commencing in 1957, fine-wool Merino ewes that were born in 1954 grazed native and improved pasture from the time of weaning of their lambs (usually late January) until the end of the period when they were joined with rams (early June). For the remainder of each year, one group each grazed (A) improved pasture, (B) native pasture, and (C) a red clover (Trifolium pratense) pasture. Records of services, lambings, and birth and weaning weights of lambs were obtained each year until the final weaning in January 1963. Lambing, as a percentage of ewes joined, declined between 1957 and 1962 from 85–88% to 66% in groups A and B and to 25% in group C. An average of 89% of ewes that lambed each year conceived to the first service. This was not influenced by years or treatments. The total number of services recorded per group was greatest for group C. Birth weights were lighter and weaning weights were heavier for the lambs of group C when compared with those of groups A and B. Ewes that failed to lamb in any year tended to fail in successive years; hence the increases in flock infertility were due to ewes becoming sterile. A number of sterile ewes had cystic glandular hyperplasia of the endometrium.
Observations were made on the effect of progesterone and pregnant mare serum (PMS) on the incidence of oestrus, the macroscopic changes in the ovaries, and the total content of gonadotrophins in each anterior pituitary gland of 105 anoestrous Romney ewes. When progesterone alone was administered for 4 days neither oestrus nor ovulation resulted. In the group receiving PMS alone, ovulation occurred in 6 of 10 ewes but none exhibited oestrus. All 10 ewes injected with both hormones ovulated; only 6 came on heat. No effect of progesterone or PMS on pituitary activity was apparent when the animals were killed 4-7 days after the last injection of hormone. Some evidence for an increase in numbers of small follicles over an 8-day period in January suggested perhaps a natural increase in ovarian activity with the approach of the normal breeding season, or a stimulatory effect of the introduction of the rams a t that time of year. Over the same period the gonadotrophic potency of the control sheep showed a slight increase. These observations are discussed in the light of current views of pituitary control of the breeding season in sheep.
Beef heifers aged 1-3 years were kept on different planes of nutrition and given progestins to synchronize ovarian cycles. Treatments included fasting for 24 or 72 hr and/or administration of PMS 0 or 4 days, before the end of the synchronization regime. Ovulations and follicles greater than 3 mm in diameter were recorded at laparotomy and slaughter. Plane of nutrition, fasting, progestin treatment, time of year, and the dose and time of injection of PMS influenced follicular development and ovulation in PMStreated heifers. PMS given before the end of the progestin regime resulted in ovulation of a high proportion of follicles. The results are discussed in relation to design of experiments concerned with understanding the physiological basis of control of ovarian function in the cow.
This paper reports an experiment examining the effect of age and protein supplementation on growth and fertility of Shorthorn-Devon cross heifers grazing natural pastures in the summer rainfall, subtropical environment of the Upper Clarence valley, north-eastern New South Wales. Heifers born over the period October to January 1963-64 were weaned in June 1964 and allotted at random within age groups (by month of birth) to a supplemented or non-supplemented treatment. The supplemented heifers were given linseed meal during the dry winter period each year from 1964 to 1966 inclusive (May-June to September-October). They were weighed each month and joined with bulls in the early summer of 1965 (2 years) and 1966 (3 years). They were examined for pregnancy in the autumn, and their calves were identified at birth. Supplemented heifers gained weight throughout and non-supplemented heifers generally lost weight in the winter periods. At two years fertility was closely related to liveweight at joining in supplemented heifers, but not in others. Heifers born in January gave the poorest reproductive performance, as the two supplemented ones that became pregnant in 1965 died at calving, and two-thirds of the non-supplemented ones were still empty after joining as 3-year-olds. The advantage of high 2-year-old fertility gained by heifers born in October and November, due to their greater size at joining, was partly offset by low fertility when lactating the following year. It is concluded that a decision as to whether a heifer should be supplemented during a period of nutritional stress prior to joining ought to be based on the probability of her reaching a prescribed target weight at joining as a result of receiving the supplement. The target weight for lactating heifers was at least 100 Ib higher than for dry hdfers. The results also indicate specific areas for further research.
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