Impact of supplementing rumen-protected arginine on blood flow parameters and luteinizing hormone concentration in cyclic beef cows consuming endophyte-infected tall fescue seed

Livestock grazing endophyte-infected tall fescue can have decreased performance due to vasoconstriction and reduced reproductive performance. Therefore, the objective of this study was to determine the effect of supplementing rumen-protected arginine to cows consuming endophyte-infected tall fescue seed on caudal blood flow and LH dynamics. Four ruminally cannulated, open beef cows (539 ± 30 kg) were used in a 2 x 2 factorial arrangement of treatments utilizing a Latin Square design with 4 periods of 31 d each. Each cow was assigned to individual pens and fed orchardgrass hay (10.3% CP and 85% NDF; OM basis) during a 10-d adaptation period, followed by a 21-d collection period in which each cow was assigned one of 4 treatments: (1) rumen-protected ARG (180 mg/kg of BW) and 1.0 kg/d of endophyte-infected fescue seed (AE+); (2) rumen-protected ARG (180 mg/kg of BW) and 1.0 kg/d of non-infected fescue seed (AE-); (3) 1.0 kg/d of endophyte-infected fescue seed (E+) alone; or (4) 1.0 kg/d of non-infected fescue seed (E-) alone. In each period, doppler ultrasound measurements for blood flow parameters were quantified on d 1, 5, 10, 15, and 19. On d 20 of each period, blood samples were collected every 10 min for 6 h and then once every hour for 12 h. Caudal blood flow exhibited an interaction (P = 0.05) of ARG × fescue seed type, resulting from an increase in blood flow in cows fed rumen-protected ARG. In addition, mean velocity was greater (P = 0.01) with the inclusion of rumen-protected ARG in the diet. Caudal artery area (P = 0.03) and diameter (P = 0.01) were decreased in cows consuming E+ compared to E- with no effect (P ≥ 0.38) by ARG supplementation. Mean serum LH concentration exhibited (P = 0.02) an ARG × fescue seed type interaction. Cows consuming E+ had decreased LH concentrations compared to all other treatments. However, cows consuming AE+ had similar LH concentrations compared to cows consuming AE- or E-. Thus, supplementing rumen-protected ARG to cows grazing endophyte-infected fescue seed has the potential to increase reproductive performance and peripheral blood flow.