The Effect of N-Carbamylglutamate Supplementation during the Last Third of Gestation on the Growth and Development of Fetuses Born to Nutrient-Restricted Twin-Bearing Ewes

Simple Summary Improvement of fetal growth in twin pregnancies is one of the major goals of extensive sheep production systems, as lambs' birth weight is correlated with their survival. This is especially relevant in harsh environments where natural maternal nutrient restriction is common. Maternal arginine (Arg) supplementation improves fetal growth, but Arg is degraded in the rumen, has a short biological half-life, and the high cost of protected forms limits its use in extensive sheep systems. N-carbamylglutamate (NCG) is not degraded in the rumen, increases arginine synthesis, and improves urea recycling, suggesting it may be an option as an alternative to Arg. The aim of this study was to evaluate the effect of oral NCG supplementation from 100 days of gestation (dga) to term in naturally nutrient-restricted grazing twin-bearing ewes, on maternal, placental, and fetal variables. The serum concentrations of NCG were increased 15-fold, and the plasma urea, albumin and phosphorus concentrations were reduced in supplemented ewes compared to controls, but there was no major effect on the dam or fetal body or organ weights nor the antioxidant markers and other blood biochemical parameters. These results indicate that NCG supplementation in mid-to-late gestation in grazing ewes was unable to rescue the negative production effects of severe natural nutritional restriction on both the dam and fetuses. The challenge of meeting the nutrient requirements of pregnant ewes in harsh environmental conditions reinforces the need for future research to identify novel strategies to improve lamb survival in such environments around the world.Abstract N-carbamylglutamate (NCG) is postulated to improve fetal growth in nutrient-restricted gestations when supplemented from day 35 to 110 of gestation, but the effects of supplementation from 100 days of gestation to birth have not been evaluated. The aim of this study was to evaluate the effect of oral NCG supplementation from 100 days of gestation (dga) to term in naturally nutrient-restricted grazing twin-bearing ewes, on the maternal body weight (BW), body condition score (BCS), placental morphology, fetal body and organ weights and blood biochemistry and antioxidant status in the ewe and fetuses. Eighteen twin-bearing ewes maintained under grazing management were randomly allocated to either a treatment group (NCG; n = 10), orally dosed once daily with 60 mg/kg of NCG from day 100 until 140 dga, or an unsupplemented control group (CON; n = 8). At 140 dga, blood gases, redox status, maternal and fetal plasma and fetal biometrics were obtained after caesarian section. The serum concentration of NCG was increased 15-fold in the NCG ewes compared to the CON. No major effects on dam or fetal body weight nor on blood biochemistry or antioxidant parameters were observed. These results indicate that NCG supplementation in mid-to-late gestation to grazing ewes was unable to rescue the negative production effects of severe natural nutritional restriction on both the dam and fetuses.