Rumen-protected arginine in ewe lambs: Effects on circulating serum amino acids and carotid artery hemodynamics.

Sixty non-pregnant, nulliparous Rambouillet ewes (51 ± 1.4 kg initial body weight) were used in a completely randomized design to determine (1) if rumen-protected Arg supplementation would increase serum concentrations of amino acids resulting from Arg supplementation and metabolism, and decrease serum concentrations of amino acids that compete with Arg for transporters, (2) if rumen-protected Arg supplementation would alter carotid artery hemodynamics, and (3) the most effective oral dose of rumen-protected Arg to positively increase both circulating amino acids and improve peripheral tissue blood perfusion as measured by carotid hemodynamics. Ewes were penned individually in a temperature-controlled facility. Ewes were randomly assigned to one of four treatments: a control group that received no supplemental Arg (CON; 50 g fine ground corn, only), or Arg supplemented groups that received 90 (90), 180 (180), or 360 (360) mg rumen-protected L-Arg•kg BW-1•d-1 mixed in 50 g of fine ground corn. Supplements were administered once daily for 14 days and fully consumed before delivery of a total pelleted diet at 0630 and 1830 daily. Baseline and final blood samples were collected at d 0 (before treatment initiation) and 15, respectively. Doppler ultrasound was used to assess carotid arterial hemodynamics at 0600 on d 0 (before treatment initiation), 5, 8, 12, and 15. After 14 days of supplementation, ewes fed 180 had greater Arg (P = 0.05) and Orn (P = 0.05) and tended (P = 0.08) to have greater Asp in serum than ewes fed 90, and for these amino acids, ewes fed 180 were similar (P ≥ 0.16) compared with ewes fed 360. All supplemented ewes (90, 180, and 360) had a negative change (P = 0.02) from baseline when normalized to CON for the pulsatility and resistance indices, which indicate greater distal tissue blood perfusion and lower vascular resistance of blood flow, respectively. Additionally, there were quadratic responses for the pulsatility and resistance indices (P = 0.03 and 0.01, respectively) where ewes fed 180 had the greatest change from baseline when normalized to CON. Results indicate Arg supplementation increased serum amino acid concentrations and improved peripheral tissue blood perfusion. The 180 mg•kg BW-1•d-1 rumen-protected Arg dose was determined to be the optimal dose for non-pregnant, nulliparous Rambouillet ewes.