Maternal oral supplementation with citrulline increases plasma citrulline but not arginine in pregnant Merino ewes and neonatal lambs

Context Arginine supplementation can counter the negative effects of fetal growth restriction in ewes bearing multiple lambs by increasing birth weight and brown adipose fat stores in lambs; however ruminal degradation limits its bioavailability and necessitates ruminal protection. The arginine precursor citrulline increases circulating arginine after a single oral dose without ruminal protection, and bolus intravenous infusion of citrulline increases maternal and fetal circulating arginine for at least 4 h post infusion. Responses to oral and chronic citrulline have not, however, been evaluated in neonatal lambs. Aims This experiment sought to determine whether orally fed citrulline would increase circulating plasma concentrations of citrulline and arginine in pregnant Merino ewes. Methods Pregnant Merino ewes were fed citrulline (CIT, 8 g/day, n = 9) or no supplement (CON, n = 9) from Day 125 of gestation (DG 125) until parturition. Ewe (DG 125) and neonatal lamb serum (<2 h old) was analysed for circulating plasma citrulline and arginine concentrations. Key results Circulating concentrations of citrulline were higher in CIT than CON ewes 4 h post feeding at DG 125, and in CIT compared to CON neonatal lambs. Despite higher citrulline concentrations, supplementation did not increase maternal or neonatal circulating arginine concentrations. Conclusions Maternal supplementation with this dose of citrulline was not effective in increasing circulating levels of arginine. Implications Further studies may be merited in pregnant sheep to determine whether higher doses of oral citrulline can increase arginine availability during gestation.