UTERINE MORPHOLOGY AND REPRODUCTIVE PHENOMENA IN RELATION TO NUMBER OF EMBRYOS AT DIFFERENT STAGES OF GESTATION IN PROLIFIC SHEEP

Forty prolific ewes of which half were superovulated with 800 IU PMSG were slaughtered on either d 30, d 70 of gestation or d 3-5 post-partu m. At each slaughter date, the ewes were balanced for number of ovulat ions ( 1 to > 3 at d 30) or embryos (1 to 4 at d 70 and d 3-5 post-par tum). Uterine length, width, surface and dry matter (DM); embryonic we ight and DM; plasma progesterone at d 15 and 30 of gestation; and prot ein concentration in allantoic fluids were measured. Superovulated ewe s averaged 5.8 CL vs. 3.1 CL for the control. On d 15 of gestation, pl asma progesterone concentration increased from 4.87 ng/ml in ewes with 2 CL to 8.02 ng/ml for those with > 7 CL. The corresponding figures a t d 30 were 4.19 and 9.44 ng/ml, respectively. Embryonic losses increa sed from 16.5% in ewes with 2 CL to 67.9% in those with > 7 CL. Length of uterine horns increased by 9.2, 7.7 and 4.1 cm for each increase i n number of embryos present at the three slaughter dates, respectively . On d 30, only embryo DM showed a significant (P < 0.05) increase wit h increased number of embryos present. On d 70, length, width and uter ine surface increased linearly with increase in number of embryos, how ever, little difference was observed between ewes carrying three and f our embryos. Ewes slaughtered after they had lambed one, two or three lambs had significantly smaller and narrower uteri than those with fou r lambs. It is concluded that, in prolific as in non-prolific sheep th e space available seems to be adequate for development of all embryos surviving the critical first 30 days of pregnancy.