D. R. LAMOND
Three groups of Merino ewes (a total of 150) kept in yards were studied for a period of 1 year. Vasectomized rams were with one group and occurrence of oestrus was noted. The presence and number of corpora lutea were observed by laparotomy at 6-week intervals. The annual rhythms in these characteristics were determined.
A second group of ewes received progesterone treatments at intervals of 6 weeks. Half the ewes were with vasectomized rams continuously but rams were with the others for only 1 week after the final progesterone injection. The period from the final injection to the onset of oestrus was determined. Introduction of rams increased the number of ewes showing oestrus at the beginning (late summer) and end (late winter) of the breeding season. The period to onset of oestrus was related to dose and frequency of progesterone injections, the time of the year, and introduction of rams. Periods to onset of oestrus became progressively longer after mid-winter (June) and a proportion of progesterone-treated ewes did not show oestrus in the 1 week period after cessation of progesterone injections in July, at a time when all untreated ewes were experiencing oestrous cycles. The implications of the seasonal change in the effects of progesterone on the ewes are discussed in relation to the sexual season.
A third group of ovariectomized ewes received progesterone followed by oestrogen, also at intervals of 6 weeks. The number of ewes showing oestrus during the period January to June was dependent on the dose of progesterone independently of the effect of dose of oestrogen. The relationship did not hold at other times. In general, there was considerable heterogeneity in mean responses and slopes of the dose-response lines.
D. R. LANG
D. R. LAMOND
An experiment was carried out to obtain quantitative information on time of ovulation after hormonal treatments at four times of the year. Four groups of Merino ewes were used in a 4 × 2 × 3×2 factorial experiment, the factors being:
- Four times in one year: July 1960, October 1960, January 1961, April 1961.
- Two doses of pms: 300 i.u., 900 i.u.
- Three doses of hcg: 300 i.u., 600 i.u., 1200 i.u.
- Administration of hcg at two different periods after pms: 24 hr, 48 hr.
All ewes were given 12·5 mg of progesterone in oil every 2 days for 2 weeks. pms was given at the time of the final injection of progesterone. The time of ovulation was determined at laparotomy at various periods after the final hormone injection.
There were no significant differences between times of year in either number of ovulations occurring during progesterone treatments or in numbers of multiple ovulations following cessation of hormone treatments.
Seasonal differences in numbers of ewes not ovulating and in the time of ovulation in the remainder were observed.
The results cannot be explained by a simple theory of seasonality in ovulating hormone production, but point to a more fundamental problem of a neuro-hormonal nature.
D. R. S. KIRBY
During delayed implantation mouse blastocysts were transferred from the uterus to the animal's own kidney. Under the kidney capsule the blastocysts `implanted' and developed normally, whilst those in the uterus remained in delay. The implications of these findings are discussed.
D. R. ACKERMAN
The enzyme hyaluronidase is believed to permit spermatozoa to disperse or to penetrate the cumulus oophorus (Kurzrok, Leonard & Conrad, 1946; Swyer, 1947a; Austin, 1948). The mechanism by which hyaluronidase mediates fertilization may not be the same in all species; Swyer (1947b) has discussed the release of enzyme by spermatozoa as a function of cell concentration, and of hyaluronidase concentration in the suspending medium. He noted that spermatozoa appear to be diffusing preformed hyaluronidase, and not to produce the enzyme. This was also the finding of Bergenstal & Scott (1948). It is well established for several species including man (Bergenstal & Scott, 1948) that hyaluronidase is a product of the seminiferous epithelium (Swyer, 1947b), and associated with spermatozoa, not with the accessory reproductive organs. In particular, the cellular enzyme was shown
R. D. LISK
D. R. LINDSAY
The sexual activity of groups of Merino, Dorset Horn and Border Leicester rams, from which weekly semen collections were made by artificial vagina, was studied at controlled temperatures from 27 to 43° C. Only Merino rams maintained sexual activity at the highest temperature (43° C). Dorset Horns recovered activity after the temperature was lowered but Border Leicesters did not. Semen motility was poor at high temperatures in all but two rams, both Dorset Horns. The Merino rams had shorter reaction times than the other breeds. There was no significant correlation between reaction time and number of ejaculates. The rectal temperatures of the Dorset Horn rams were 0·3 to 0·4° C lower than those of the Border Leicesters; Merinos were intermediate.
At a given ambient temperature, rams had lower rectal temperatures after severe heating than before, apparently owing to increased thermoregulatory ability. Mounting and ejaculation resulted in virtually no rise in rectal temperature.
D. R. LAMOND
Hereford heifers in yards were given progesterone for periods of 2 weeks, at intervals of 7 weeks over a period of 1 year. Seasonal changes in the effects of progesterone were observed. During the late winter and spring months the ovarian cycles were not suppressed by doses of progesterone that were satisfactory at other times of the year. The interval from the cessation of treatments to onset of oestrus was also shorter in the late winter/spring period.
D. R. LAMOND
Injections of progesterone were given to ewes to suppress ovarian cycles; pregnant mare serum gonadotrophin (pms) was administered within 2 days of the final injection of progesterone. Oestrus, numbers of ovulations and follicle growth were observed during the week following treatment. In some experiments, ewes were mated to fertile rams and fertility and fecundity were recorded. Experiments were carried out at different stages of the breeding season.
Relationships between methods of suppression of ovarian cycles (dose and frequency of injections of progesterone) and methods of ovarian stimulation (dose and time of administration of pms in relation to the final progesterone injection) for each of the responses were examined. The most important finding was that for comparable dosage levels of pms, the numbers of ovulations were greater after progesterone injections on alternate days than after daily injections. Stage of the breeding season and introduction of rams influenced the results.