Nutritional stress and pre-implantation embryonic mortality in Merino sheep, 1965

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Abstract
SUMMARY Of 120 mature Merino ewes, balanced groups received the following treatments from days 8 to 15 after fertile mating: 1, submaintenance nutrition plus 10 mg/day progesterone; 2, submaintenance without progesterone; 3, maintenance nutrition plus progesterone as above; 4, maintenance nutrition without progesterone. The ewes were in light condition, they lost some weight before mating, they had an ovulation rate of 108·3% and they barely maintained their mating weight during the first 3 months of pregnancy. The percentages of ova shed not represented by lambs at term were 60·6, 58·1, 48·5 and 62·5 for groups 1–4 respectively. There were no significant treatment differences or interactions. The high overall loss of ova could have been due in part to depressed fertilization rate: however, the general environmental conditions and low body weight of the ewes seems likely to have made an important contribution to the high basal loss. There was a significant regression of prenatal mortality on body weight at mating, but no detectable relationship between prenatal mortality and condition score. Sixteen oestrous cycles of over 21 days were distributed through all groups, indicating that considerable mortality occurred after day 13.