The effect of N-carbamylglutamate supplementation during the last third of gestation on maternal nutritional status and colostrum quality of nutrient-restricted twin-bearing ewes

Maternal nutrient restriction in twin-bearing ewes reduces the colostrum protein content, resulting in reduced postnatal growth and greater lamb mortality in twin- compared with single-bearing ewes. N-carbamylglutamate (NCG), an analogue of N-acetylglutamate increases endogenous arginine synthesis and is postulated to influence fetal growth and development and potentially lamb survival. The effect of maternal supplementation with NCG in mid-late gestation on colostrum quality and nutrient status of nutrient-restricted ewes has not been reported. The aim of this study was to evaluate the effect of oral maternal supplementation with NCG during mid–late gestation in nutrient restricted twin-bearing ewes on maternal body weight (BW) gain, body condition score (BCS), nutritional status and colostrum composition. Twin-bearing ewes (n = 20), managed in individual pens, were orally dosed once-daily with 60 mg/kg BW NCG in a water carrier from 100 d of gestation (dg) to lambing and were compared with unsupplemented controls (CON; n = 21). The ewes received a ration based on alfalfa (12.12% CP and 2.10 Mcal/kg ME) and pasture (6.85% CP and 2.13 Mcal/kg ME) hay, covering 50% of National Research Council nutritional requirements for twin-bearing ewes to reflect commercial conditions. Maternal BW and BCS were recorded every 10 d, from 100 dg until lambing. Maternal blood samples were collected at 130 dg and 30 min after lambing and plasma beta-hydroxybutyrate (BHB), total protein, albumin and urea were evaluated. Colostrum was collected 30 min after the second lamb was delivered and fat, non-fat solids, density and protein contents were determined. The effect of treatment on ewe BW, BCS were analyzed using REML analysis in R (lme4 R package) with time (dg) and treatment (and their interaction) as fixed effects. Plasma and colostrum metabolites were analyzed using REML with treatment as the fixed effect. Ewe BW increased (P < 0.0001) and BCS decreased (P < 0.0001) with advancing gestation, but there was no effect of treatment (P > 0.05). At 130 dg plasma urea was a 12% greater (P = 0.02) and albumin tended to be 4% greater (P = 0.08) in NCG compared with CON ewes, but no treatment effect on BHB or total protein content was observed (P > 0.05). No treatment effect on maternal plasma metabolites were observed post lambing (P > 0.05). Colostrum protein content was 21% greater in NCG compared with CON (P = 0.04) ewes, but fat, non-fat solids or density (P > 0.05) did not differ between groups. Collectively, these results suggest that supplementation of nutritionally restricted ewes with 60 mg/kg BW from 100 dg to lambing may alter maternal nitrogen metabolism and colostrum protein content. The potential impact of these changes on lamb growth and/or survival, warrants further investigation.