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Various prenatal factors including the number of littermates (fraternity size) and exposure to male littermate (fraternity sex ratio) during fetal period have been reported to influence postnatal fertility in the mammals. The present research was conducted to study the association of fraternity size and sex ratio with reproductive performance of nulliparous ewes and does. To this end, data associated with number of littermates, exposure to male littermate, birth weight, age at first pregnancy, as well as litter size, sex ratio of offspring, litter weight, and birth weight of female and male offspring after the first parturition retrieved from the database of sheep (n = 536 Romane and 289 Blanche du Massif Central ewes) and goat (n = 174 Alpine and 267 Saanen does) flocks. Fraternity size was negatively associated with birth weight of ewes and does (P < 0.05). Exposure to male littermate during fetal period was associated with younger age at first pregnancy and larger litter size in the does (P < 0.05), but not in the ewes (P > 0.05). Exposure to male littermate during fetal period was positively associated with the odds of male-biased litters in the ewes and does (P < 0.05). Fraternity size was positively associated with litter weight in the does (P < 0.05), but not in the ewes (P > 0.05). In conclusion, the present study showed that the number and sex of littermates during fetal period could impact postnatal reproduction of ewes and does. In this context, some associations, particularly those related to exposure to male littermate during fetal period, were only observed in does, which implicates that the effect of androgens on developmental programming of reproduction may be species-specific., Competing Interests: Declaration of Competing Interest The authors have no conflict of interest to disclose., (Copyright © 2024 Elsevier B.V. All rights reserved.)