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Synopsis An experiment is reported in which hatching eggs were stored in a room at 12.7° ± 1.1° C. for up to 3 weeks after storage on the farm for 2 to 5 days. The eggs were stored in the room on keyes trays in part open‐sided wooden boxes or in sealed Cryovac bags or in sealed Cryovac bags flushed out with nitrogen before sealing. It was found that the normal decline in hatchability with storage time was reduced by storage in bags. There was no difference in hatchability between bags with or without nitrogen though there was an indication that the proportion of cull chicks at hatching was reduced by storage in bags flushed out with nitrogen for eggs stored more than 8 days. The effect on hatchability of the storage in bags is pinpointed as resulting from reduced embryonic loss between fertilisation and the 2nd day of incubation. This disagrees with a previous result and it is suggested that differences in genetic origin of eggs may account for differences in time of effect of storage treatment.

1. Twenty-four Merino ewes acclimatized to a hot environment were compared with twenty-four kept at normal temperatures, with respect to ovulation rate and embryonic loss by 25 days' pregnancy. Possible modifying effects of the three subsidiary factors, thyroxine level, vitamin A intake and progesterone level, were sought. The design of the experiment was a balanced factorial one.2. While the differences between the hot-room and yard groups as a whole were not significant, in the former there were fewer ovulations, a smaller proportion of the potential embryos actually began to develop and, of these, a larger proportion had died by 25 days' pregnancy. Consequently only thirteen hot-room ewes contained live embryos compared to twenty in the yard; the total numbers of live embryos were fourteen and twenty-seven, respectively.3. Of the subsidiary factors only thyroxine produced any marked effect. Both in the hot-room and in the yard the proportion of potential embryos developing and the proportion of actual embryos surviving at 25 days' pregnancy were greater where thyroxine injections were given. There appeared, however, to be no effect on ovulation rate. There was a significant increase in the proportion of hot-room ewes with live embryos due to thyroxine. Grouping hot-room and yard ewes together, thyroxine injections were associated with a significant increase in the proportion of potential embryos developing and in the proportion of actual embryos surviving; also, consequently, in the proportion of ewes with live embryos.4. The results are discussed in relation to published work on the effects of high temperatures on reproduction.

A single oral dose of mestranol (l7ct-ethynylestradiol 3-methyl ether) was administered to two groups of eight adult female beagle dogs each on Day 6 or 21 after first acceptance of the male. Based on corpora lutea counts, embryonic loss was 95.5 and 67.3%, respectively, for the two treatment groups, and only 34.5% for the control. In a second study a group of 12 beagles were used to determine the effect of mestranol on ova transport. Nine bitches were dosed on Day 6 and the reproductive tracts were removed between 1 and 5 days later and three controls were examined on Day 11. Thirty-nine of a possible 56 ova were flushed from the tracts of the treated females and all but one were from the oviducts. Eighteen (46%) of the ova were degenerating. The controls produced 17 normal zygotes out of a possible 24, and all were flushed from the uteri. Mestranol apparently did not accelerate ova transport, and the possibility of both a direct effect on the ova and an indirect effect via a delay in ova transport is discussed.

Normal pregnant guinea pigs were killed on gestation days 12–20 and examined for implantation sites and resorbing embryos. Their ovaries were removed and serially sectioned, and the functioning corpora lutea counted for comparison with the number of conceptuses. It was found that a single corpus luteum was associated with two implantation sites with a frequency of 9.55%. Embryonic loss prior to implantation was 12.6% and the value for resorption following implantation varied from 5.8 to 7.2% depending on the time of killing and the method employed for determining resportion. A count of functioning corpora lutea facilitated the determination of embryonic loss prior to implantation, but offered little advantage over simpler techniques for determining resorption after implantation.

Summary A total of 837 services were analyzed for the effects of sire and system of mating on estimated embryonic mortality by 150 days of gestation. The sire had a highly significant effect on the rate of embryonic death in the females to which he was bred. Outbred embryos had an estimated death rate of 19.8% by 150 days as compared-to 22.3% for inbred embryos. Outbred dams had 19.2% embryonic death by 150 days, whereas embryonic mortality in inbred dams was 28.4%. Although the difference between outbreds and inbreds was not statistically significant in either case, the trend was for inbreeding of either embryos or dams, particularly the latter, to increase embryonic mortality.

1. Embryonic mortality and reproductive performance were studied in 150 mature Merino ewes, groups of which were restricted to approximately 15% of their maintenance requirement from days 0to7 (group 1), 6to13 (group 3) and 13to20 (group 4) respectively. Groups 2and5 were controls. Ovulation point counts, returns to service, pregnancy test by laparotomy at day 40 and lambing performance were used to assess and apportion the embryonic loss.

White Leghorn pullets were fed standard diets supplemented with 0.0%, 0.1%, 0.5%, and 1.0% levels of dietary caffeine. The two highest levels of caffeine caused the production of soft-shelled eggs and a cessation of egg production within 3 days. Although 0.1% caffeine did not effect fertility, it significantly increased embryonic mortality over a 14-day period following a single insemination.

White Leghorn pullets were fed standard laying rations supplemented with 0.0%, 0.05%, and 0.1% levels of dietary caffeine. There was no statistical difference in fertility among the three groups. Embryonic loss in eggs from pullets fed 0.05% caffeine was between values previously reported for 0.0% and 0.1% dietary caffeine. This suggests that embryonic mortality increases as levels of caffeine are increased in the diet up to 0.1%.

A series of studies was conducted in 1968 and 1969 to compare fertilization rates, return rate, and sperm distribution in the genital tract in Bungaree and Peppin Merino ewes. Differences in lambing rates of the two ewe strains were demonstrated, but there was no major difference in fertilization rate in either year. A significantly higher proportion of Bungaree ewes had less than 1000 sperm in the fallopian tubes 24 hours after service, but there were no significant differences in any other character examined. Contrary to an earlier report, fertilization failure is unlikely to have been a major cause of a difference in the fertility of the two strains in the two years, and embryonic loss is likely to have made a significant contribution to the difference in their fertility.

Ewes which fail to lamb can be classified as failing to conceive (ENC) or conceiving but failing to carry at least one embryo to full term (ENE). Estimates of ENE have been made indirectly from mating and lambing records involving 2509 observations over 3 years in a flock of medium Peppin Merinos. Estimates of ENE and of individual embryo loss have been made directly from autopsies of 419 ewes in the same Peppin flock and in one of mixed strains. The indirect estimate of ENE (ewes served and expected to have conceived but failing to lamb, as a percentage of ewes joined) averaged 4.3% for ewes aged 1½–9½ years at joining. Two measures of early embryonic loss were obtained from the autopsies of ewes expected to have been pregnant for approximately 28 days: (i) Ewes predicted not to lamb, as a percentage of ewes expected to have conceived, gave an estimate of 2.8–3.9 % at 1½ years, and 10.1–12.0% at 8½–11½ years. (ii) By relating the number of active corpora lutea to the number of healthy embryos, the estimates of loss obtained were 4.7–5.8% for maidens and 18.6–20.6% for aged ewes. From approximately 28 days to term no significant foetal loss from resorption or abortion could be demonstrated by comparing autopsy predictions with observed performance in ewes proceeding to term, though a very small loss of one of a pair of twins may have occurred in ewes aged 1½ years. Ewes with two active corpora lutea suffered a significantly greater loss of embryos than did ewes with one. With the corpus luteum as the unit, the loss in maiden ewes was 20.0% with two corpora lutea and 2.9–4.1% with one, the corresponding figures for aged ewes being 34.7–36.1 and 9.0–11.5%. These differences are not evident with the ewe as the unit, as a ewe with two corpora lutea which had lost one embryo would remain in the group predicted to lamb. Estimates of ENE from autopsy were made on ewes selected from the complete flock because they had not returned to service. Estimates for the same ages on the complete flock were 3.6–4.5% for maiden and 8.7–10.2% for aged ewes. Calculations of ENC have been based on the estimate of ENE made here and on previously reported figures of the numbers of dry ewes per ewe joined and present at lambing. Ranges of ENC were 13.6–14.5% at 2 years, and 3.3–4.8% respectively. No identical twins were observed at autopsy, and there is no reason to believe that any would have been present at any earlier stage of pregnancy.