Ovulation induction protocol using equine chorionic gonadotropin and porcine luteinizing hormone in the weaned sow

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Objective: To determine the lowest dose of porcine luteinizing hormone (pLH) that induces ovulation in a predictable manner in mixed-parity sows 80 hours after treatment with equine chorionic gonadotropin (eCG) at weaning. Materials and methods: All sows were injected intramuscularly (IM) with 600 IU eCG at weaning. At 80 hours post weaning, sows were treated IM with pLH at doses of 0.625 mg (n = 5), 1.25 mg (n = 14), 2.5Â mg (n = 21), and 5.0 mg (n = 5). The 15 controls were untreated. Approximate time of ovulation was determined using transrectal realtime ultrasound 8 hours before and 16 hours post pLH injection, and thereafter at 8-hour intervals until ovulation was confirmed. Results: Administration of pLH was effective in inducing ovulation in weaned sows. The pLH-to-ovulation interval was shorter in sows given pLH at 1.25 mg (P < .05), 2.5 mg (P < .01), and 5.0 mg (P < .05) than in controls. Variance associated with the pLH-to-ovulation interval tended to be less in treated than in control sows (P < .10). More sows administered either 2.5 or 5.0 mg pLH ovulated by 40 hours post pLH administration than all other treatments (P < .01). Implications: Doses of 2.5 and 5.0 mg of pLH did not differ in their effect of inducing ovulation in an estrus-synchronization program initiated with 600 IU of eCG at weaning. Controlling the time of ovulation allows insemination to occur at the time of optimal fertilization.