49. N-carbamylglutamate and Melatonin Supplementation Alters Peripheral Blood Flow in Lambs Without an Apparent Benefit to Heat Stress

Abstract Recently, combined supplementation of N-carbamylglutamate (NCG) and Melatonin (MEL) have demonstrated beneficial effects in vasodilatory properties; nevertheless, its potential usage to treat hyperthermia in heat-stressed animals remains underexplored. Therefore, the objective of this study was to evaluate the effects of NCG and MEL supplementation on carotid artery hemodynamic and physiological indicators in heat-stressed lambs during a 42-day trial period. We hypothesized that the NCG and MEL supplementation will increase peripheral blood flow to facilitate heat dissipation and alleviate heat stress decreasing rectal temperatures. Four month old commercial Dorper ram lambs (n = 35) were assigned to three different treatment groups: a cooled control group housed under shade without supplementation (CL-CON, n = 11), a group housed without shade and without supplementation (HS-CON, n = 11), and a group housed without shade receiving a supplementation of 1.4 g/h/d N-carbamylglutamate and 8 mg/h/d of melatonin (HS-NCGMEL, n = 13). On day 40±2 d posttreatment, hemodynamic measurements of the right carotid artery were assessed at 1600h via Doppler ultrasonography while respiration rates (RR), heart rate (HR), and rectal temperature (RT) were recorded at 0400h and 1600h as physiological indicators. The model evaluated the fixed effect of treatment using blood flow as a dependent variable; whereas RR, HR, and RT data were analyzed using repeated measures by the MIXED procedure of SAS and the model included treatment, time of day, and their interactions. A significant difference in carotid artery blood flow was observed between groups (P = 0.0351) where HS-CON had decreased blood flow (281.65±21.17 mL/min) compared with CL-CON (358.94±22.19 mL/min) and HS-NCGMEL (340.25±19.54 mL/min). Interestingly, no difference was observed between CL-CON and HS-NCGMEL lambs (P > 0.05). Rectal temperatures were increased (P = 0.0004) in HS-NCGMEL (40.19±0.11ºC) when compared with CL-CON (39.60±0.12ºC) and HS-CON (39.89±0.12ºC). Similarly, heart rates were increased (P = 0.0063) in HS-NCGMEL (122±7 bpm) compared with CL-CON (105±7 bpm) and HS-CON (117±7 bpm). All groups experienced increased respiration rates in the afternoon (P < 0.0001), with HS-NCGMEL having the greatest increase (P < 0.0001) compared with CL-CON and HS-CON (207±8 bpm, 150±8 bpm, 181±8 bpm; respectively). Contrary to our hypothesis, these results indicate that treated animals experienced an increased thermoregulatory response perhaps due to increased metabolic activity rather than alleviation of heat stress.