Early reproductive failure of ewes in a hot environment IV. The ovary

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Abstract
1. A balanced factorial experiment was carried out with 48 Merino ewes. There were two levels of each of the four factors: environmental temperature, thyroxine status, vitamin A intake and progesterone status. Each ewe was killed at 25 days' pregnancy. The ovaries were removed, weighed and examined histologically.2. There were no significant treatment effects on ovarian weight, corpus luteum diameter, lutein cell frequency, lutein cell nuclear diameter, the number of Graafian follicles exceeding 0·9 or 1·9 mm. diameter, or mean follicle diameter. The results suggest that with more animals heat might prove to depress ovarian weight and vitamin A to increase ovarian weight, corpus luteum diameter and the number of large follicles.3. There were no significant differences between the mean values for those ewes with live embryos and those with dead ones with respect to any of the above indices.4. The results support the conclusion that variations in embryonic viability due to the experimental treatments were not mediated primarily through variations in ovarian hormone secretion.