134. Preconceptional Maternal Nutrition Affects Postnatal Growth Performance in Singleton Female Lambs.

Abstract Maternal nutrition prior to conception is increasingly recognized as an important window for developmental programming, with the potential to influence offspring growth and later reproductive development. While the effects of gestational nutrition on offspring growth performance are well studied, less is known about whether short-term alterations in maternal energy intake before conception affect offspring growth before and after weaning. This study examined the impact of maternal preconception nutrition on offspring postnatal growth performance from birth to weaning, with a specific focus on singleton pregnancies. Crossbred Polypay×Dorset ewes (n = 99) were assigned to one of three dietary treatments during the suboptimal breeding season (Northern Hemisphere) and fed different nutritional diets for 21 days prior to mating: control (CON:100% of maintenance energy), undernutrition (UN:50%), or overnutrition (ON:200%). Following breeding, all ewes were managed under common nutritional conditions throughout gestation and lactation. Across treatments, 113 lambs were born, of which 57 were females (singletons:27 and twins:30). Dams and progeny were housed together until weaning (range: 54 to 74 days old). Lambs consumed milk and had unlimited access to a creep diet formulated to deliver 11.5 MJ of metabolizable energy per kg of dry matter, containing 15% protein and mineral supplementation to support growth up to weaning. Weekly weights from birth to weaning from female singletons (UN:10; CON:8; ON:5) were used for analyses including birth weight, weight gain, and body mass index (BMI). BMI was used as a composite measure of body mass relative to skeletal size and served as a proxy for body condition during early growth. Each animal was considered the experimental unit, and data were analyzed using ANOVA procedures and mixed models with repeated measures in SAS. Significance was declared at P ≤ 0.05. Birth weight (UN:5.3±0.13; CON:4.9±0.36; ON:4.9±0.25) and birth BMI (UN:0.66±0.05; CON:0.53±0.04; ON:0.62±0.05) did not differ among treatments (P > 0.05). Weaning weight (UN:28.9±1.17; CON:25.3±1.31; ON:29.0±1.40 kg) tended to differ among treatments (P = 0.09), while BMI (UN:1.1±0.16; CON:1.4±0.16; ON1.3±0.19) differed among treatments (P ≤ 0.05). Live weight gains across the experiment did not significantly differ among maternal nutritional treatments (UN:18.8±0.70; CON:16.4±0.71; ON:17.6±0.59 kg; P ≤ 0.05). Collectively, these findings indicate that short-term alterations in maternal energy intake prior to conception do not affect offspring size at birth but are associated with differences in body condition by weaning, suggesting maternal nutritional status before conception may influence early growth patterns in singleton offspring. These early differences in growth and body condition may represent one pathway through which preconception nutrition contributes to developmental programming of later reproductive function.