Plasma fatty acids and reproductive performance of lactating beef cows fed rumen-protected fat

Two experiments were conducted to evaluate the effects of rumen-protected fat (RPF) supplementation after or during estrus synchronization on plasma fatty acid concentrations and reproductive performance of lactating beef cows. In Exp. 1, primiparous (n = 59; 495 ± 50 kg) and multiparous cows (n = 43; 552 ± 64 kg) were used in a randomized complete block design. On d -10, cows were stratified by BW and age to receive either a beet-pulp-based supplement fed at 1.8 kg/d per cow (control) or a beet-pulp-based supplement containing RPF at 1.4 kg/d per cow. Cows were estrus synchronized from d -10 to -3, with timed AI on d 0. On d 0, cows were transferred to bromegrass pastures and supplemented for 30 d. In Exp. 2, multiparous cows (n = 168; 525 ± 62 kg) were used in a randomized complete design and estrus synchronized similarly as in Exp. 1. However, cows were supplemented from d -10 to 10 after timed AI. In Exp. 1, plasma concentrations of 18:2n-6 tended to be greater (P = 0.07) for cows fed RPF than for control cows after 30 d. In Exp. 2, plasma concentrations of 18:2n-6 and total fatty acids were greater (P ≤ 0.002) for cows fed RPF after 20 d of supplementation. In Exp. 1 and 2, reproductive performance was similar (P ≥ 0.72) between treatments. Rumen-protected fat fed to lactating beef cows during and after estrus synchronization increased plasma fatty acid status; however, the increased fatty acid status was not sufficient to improve reproductive performance of lactating beef cows.