Effects of short- or long-term infusions of acetate or propionate on luteinizing hormone, insulin, and metabolite concentrations in beef heifers

Two trials were conducted to evaluate the effects of short- (Trial 1) or lo ng-term (Trial 2) intraruminal isocaloric infusions of acetate or propionat e on secretion of LH, insulin, and selected metabolites in short- or long-t erm energy-restricted beef heifers. In Trial 1, 16 Angus heifers were assig ned on d 6 to 12 of a synchronized estrous cycle (estrus = d 0) to a body w eight-maintenance (BWM; n = 4) or an energy-restricted, body weight-loss (B WL; n = 12) treatment. On d 12 of a synchronized estrous cycle, heifers rec eived PGF(2 alpha) to synchronize estrus, and 12 h later BWL heifers receiv ed intraruminal, isocaloric infusions of acetate, propionate, or vehicle fo r 6 h and BWM heifers received vehicle concurrently. Mean plasma LH and LH pulse frequencies and amplitudes were not affected by treatment (P > .05). In contrast, infusion of propionate increased plasma insulin (P < .05) and reduced plasma concentration of NEFA (P < .05). In Trial 2, six ovariectomi zed Angus heifers were energy-restricted for 30 d. On d 14 and 26 of restri ction, heifers began receiving intraruminal isocaloric infusions of acetate or propionate for 96 h in a switchback approach. Intraruminal infusions of vehicle for 6 h preceded infusions of acetate or propionate. Jugular blood was collected at 12-min intervals during infusions of vehicle and during t he last 6 h of infusion of acetate or propionate. Mean concentration of LH and amplitude of pulses of LH were lower during acetate vs propionate or ve hicle infusion (P < .05). Infusion of propionate increased insulin relative to acetate or vehicle infusion (P < .05). Plasma NEFA were reduced by infu sion of propionate (P < .05) and increased by infusion of acetate (P < .05) .