Use of a five-day progesterone-based timed AI protocol to determine if flunixin meglumine improves pregnancy per timed AI in dairy heifers

Two experiments were conducted to test the hypothesis that the 5 d Co-Synch + CIDR (Controlled Internal Drug Release insert containing progesterone) protocol could be applied as an efficient timed AI (TAI) protocol in dairy heifers, and that treatment with flunixin meglumine (FM) during the period of CL maintenance would increase pregnancy per TAI (P/TAI) and late survival of embryos. Objectives were: 1) in Experiment 1, to compare P/TAI with the 5 d Co-Synch + CIDR protocol to a PGF_2α/GnRH protocol; and 2) in Experiment 2, to determine if FM administered 15.5 and 16 d after first TAI would increase P/TAI, using the 5 d Co-Synch + CIDR protocol with a new or previously used (5 d) CIDR insert. In Experiment 1, 248 heifers were assigned randomly to either the PGF_2α/GnRH protocol (n = 120) or the 5 d Co-Synch + CIDR protocol (n = 128). Pregnancy per TAI did not differ between the 5 d Co-Synch + CIDR protocol (53.1%) and the PGF_2α/GnRH protocol (45.8%; P = 0.22). In Experiment 2, 325 heifers synchronized with the 5 d Co-Synch + CIDR protocol were assigned randomly to receive two injections of FM (FM group; n = 158) at 15.5 and 16 d after TAI, or to remain as untreated controls (n = 165). Pregnancy per TAI in Experiment 2 was 59.4 and 59.5% at 45 d for control and FM groups, respectively, with no differences between groups (P = 0.83). The 5 d Co-Synch + CIDR protocol resulted in an acceptable P/TAI in dairy heifers. However, FM did not improve P/TAI in dairy heifers.