Prolificacy-survival trade-off in Morada Nova sheep under Brazilian semiarid conditions

We used long-term data from 13 Morada Nova sheep flocks monitored between 1999 and 2015 in the Brazilian semi-arid region to evaluate how prolificacy and seasonality shape maternal reproductive output and progeny survival. For each ewe lambing event, we quantified total progeny weight at birth (PWB) and weaning (PWW), as well as survival rates at birth (PSRB) and weaning (PSRW), and classified births as occurring in the dry or rainy season. Ewes with single births showed lower PWB and PWW, but higher PSRB and PSRW, than ewes with multiple births (p < 0.0001). When the number of lambs at birth was included as a covariate, each additional lamb was associated with an increase of 1.74 kg in PWB and 3.51 kg in PWW (p < 0.0001), but also with an absolute reduction of 6% points in PSRB and 17% points in PSRW, findings that are consistent with a trade-off between litter size and offspring survival. Ewes with multiple births were more productive in terms of total kilograms of lamb weaned, despite lower survival rates per offspring. No significant association was found between type of birth and progeny across seasons (χ² test: p > 0.05). However, the number of lambs weaned differed slightly between seasons (p = 0.014), with marginally higher values in the dry period (1.65) than in the rainy period (1.60), although the magnitude of this difference was small. In Morada Nova ewes, multiple births increased total weaned lamb biomass but were associated with reduced progeny survival, indicating a trade-off between prolificacy and lamb viability. Intermediate prolificacy provided a more balanced compromise between productivity and survival under semiarid conditions.