926
Effect of an injectable trace mineral on pregnancy rate of virgin heifers when synchronized using the 5 day Co-Synch plus CIDR or 14 day CIDR-PG protocol
This study examined the effect of using a commercially available injectable trace mineral (TMI) on the reproductive performance of virgin heifers. Angus-crossbred heifers (n = 109, BW = 358 ± 3.7 kg) were blocked by weight and randomly assigned to treatment in a 2×2 factorial of either TMI containing copper, manganese, selenium, and zinc or no injection (CON) and one of two synchronization protocols, either a 14d CIDR-PG protocol or a 5d Co-Synch plus CIDR protocol. The objective of this study was to determine the effects of TMI prior to fixed time artificial insemination (AI) on conception to AI as well as the effects on overall pregnancy rate after exposure to bulls. Thirty-three days prior to AI, heifers receiving TMI were given Multimin®90 (0.57 mL/45.5 kg of BW). For the 14d CIDR-PG protocol, a controlled internal drug release device (CIDR) was inserted 33 days prior to insemination and removed 14 days later. Prostaglandin (PG) was injected 16 days after CIDR removal and heifers were artificially inseminated 73 h later. For the 5d protocol, a CIDR was inserted 7d prior to AI and an injection of gonadotropin-releasing-hormone (GnRH) was given. Five days later the CIDR was removed and a PG injection was given. A second PG injection was given 5.6 h later and heifers were artificial inseminated 55 h after the last PG injection. All heifers received an injection of GnRH concurrently with AI and exposed to bulls 9 days post AI. Conception was determined using ultrasonography at 55 and 105 days post-AI. At 105 days post-AI there was a synchronization protocol by TMI interaction for rate of heifers conceiving to AI (P = 0.04). However, conception to AI within the 5d Co-Synch plus CIDR protocol (CON 66.0% vs. TMI 52.0%) and within the 14d CIDR-PG protocol (CON 55.0% vs. TMI 75.0%) did not differ (P ≥ 0.13)between the CON and TMI. There was no interaction (P = 0.18) between synchronization protocol and TMI for overall pregnancy rate after timed-AI and natural service. However there was significant effect of TMI (P = 0.02) on overall pregnancy rate with heifers receiving TMI (93.0%) having a greater (P= 0.02) pregnancy rate than the CON (83.0%) after AI and exposure to bulls. This data suggests that use of a TMI 30 days prior to the breeding season may improve reproductive performance of virgin heifers.
Keywords:
Heifer, Injectable trace mineral, Reproduction