Energy metabolism and ruminal fermentation of prolific ewes in response to scheduled increase, relative to lambing, of dietary energy source and concentration

In late gestation, to prevent metabolic disorders in prolific ewes, energy intake must align with increased energy requirements to support the growth of multiple fetuses. The present study was conducted to evaluate if providing a high-concentrate diet as early as 4 compared with 2 weeks prepartum was more effective to meet the energy requirements of prolific breeds, and if corn silage could serve as a high-energy feed for late gestational ewes. Eight weeks prepartum, 48 mature F1 crossbred (Dorset × Romanov) ewes were offered grass-legume silage ad libitum. Four weeks later, ewes were randomly assigned to 1 of 3 isoenergetic dietary treatments: a grass-legume silage and ground corn-based total mixed ration (TMR) from week -4 (GC4; gradual increase from week -5) or week -2 (GC2; gradual increase from week -3) or a corn silage-based TMR from week -4 (CS4; gradual increase from week -5). Dry matter intake (DMI), body condition score (BCS), circulating beta-hydroxybutyrate (BHB), glucose, and non-esterified fatty acids (NEFAs) were monitored throughout the last 6 weeks of gestation. Rumen fluid was collected at week -2 to assess fermentation parameters. Inclusion of concentrates at 4 (GC4) compared with 2 weeks prepartum (GC2) resulted in greater DMI and metabolizable energy intake (MEI) from weeks -5 to -3. Overall, during the last 5 weeks of gestation, DMI and MEI of GC4 ewes were 12 and 20% higher compared with GC2, respectively. At week -4, circulating BHB concentrations were greater for GC4 compared with GC2, despite an improved energy balance, as confirmed by lower NEFA and greater glucose concentrations. Except for a decreased DMI and MEI at week -4, resulting in greater NEFA concentrations for CS4 compared with GC4, no other impact of energy source on intake or circulating NEFA and glucose was observed during the prepartum period. Compared with GC4, BHB concentrations were greater for CS4 from weeks -5 to -1. Rumen proportion of acetate decreased by 7%, whereas butyrate increased by 22% for CS4. The current experiment demonstrates that blood BHB concentration was affected by dam energy balance and ingredient composition of the diet. Our study also shows that a high-energy corn silage diet provided from 4 weeks prepartum can prevent the onset of a negative energy balance during late gestation, similar to adding ground corn to a grass-legume silage-based diet.