260 Investigating the impacts of poor maternal nutrition on ewe lamb reproductive capacity.

Abstract Extensively managed ewes are often grazed through winter, which coincides with gestation and producers often supplement ewes at the end when nutrient demands are the highest, to support maternal maintenance and fetal growth. However, it is likely that as range decreases in quantity and quality across winter months, ewes experience nutrient challenge prior to this traditional supplementation period. Thus, the objective of this study was to determine the impact of maternal nutrient challenge during gestation on indicators of reproductive capacity in ewe lamb offspring. At 30 days of gestation (dGA), pregnant ewes were blocked by bodyweight and assigned a diet based on National Research Council (NRC) requirements, that either met all nutritional requirements for gestation or a diet that simulates winter forage, meeting approximately 50% of protein and ~70% of total digestible nutrient (TDN) requirements, to create CON (n =18) and NC (n=12) lambs, respectively. Beginning at 6 mo of life, ewe lambs were bled bi-weekly and plasma was isolated. Plasma progesterone concentration were quantified by ELISA and used to determine puberty attainment. Puberty was considered attained when progesterone concentration exceeded 1 ng/ml in for two cyclic patterns. After puberty attainment, lambs were harvested, and reproductive weights and tissues were collected for histology and transcript analysis. There were no differences final live weight, hot carcass weight, or gross weight of reproductive organs at harvest. Preliminary follicle classifications did not differ, however, there was a numerical increase in the primordial and total follicle populations of NC lambs compared to CON. Relative transcript abundance of Erα tended (P < 0.10) to be increased and Erβ was increased (P < 0.05) in NC lambs compared to controls, while PCNA and AMHr did not differ. Conversely, protein expression of Erα and Erβ was decreased (P < 0.05) in NC lambs compared to CON lambs. Despite an increase in gene expression, there is a decrease in protein synthesis suggesting an issue with the translation of mRNA into protein. The selected gene code for synthesis of receptors for hormones that regulate folliculogenesis and reduced receptor presence could precede between animal variation in reproductive capacity. Our preliminary findings suggests that if range ewes experience nutrient challenge earlier than the traditional supplementation period, offspring ewe lambs may have impaired fertility.