The ischiorectal fossa: an alternative route for the administration of prostaglandin in cattle.

Three experiments were conducted to investigate the ischiorectal fossa (IRF) as a route for the administration of prostaglandin F2 alpha (dinoprost) in cattle. In Experiment 1, 21 nonlactating Holstein cows were given 100 micrograms of gonadotropin releasing hormone (GnRH), intramuscularly (i.m.), and, 7 d later, 25 mg of dinoprost into the IRF. Sixteen cows had serum progesterone concentrations > or = 1.0 ng/mL at the time of dinoprost treatment, and all of these had rapid and complete luteolysis; the other 5 cows were not considered to have a functional corpus luteum (CL) at the time of treatment. There were minimal adverse behavioral reactions to the IRF injections and no visible or palpable tissue reactions at the injection site. In Experiment 2, 74 Holstein heifers were given 25 mg of dinoprost by IRF injection. Luteolysis occurred in 84.3% of the heifers with a functional CL (as determined by the serum progesterone concentration at the time of treatment). Of the heifers bred by either natural service or artificial insemination, 61.8% became pregnant. In Experiment 3, 48 beef heifers received dinoprost 7 d after ovulation, as follows: 25 mg, i.m. (n = 9); 25 mg, IRF (n = 10); 10 mg, IRF (n = 10); 10 mg, subcutaneously (s.c.) (n = 10); or 10 mg, intravulvosubmucosally (IVSM) (n = 9). Fewer heifers (P < 0.05) were found to be in estrus or ovulating in the 10 mg IVSM group (0% and 11%, respectively) than in the 25 mg i.m. group (100% and 100%), the 25 mg IRF group (90% and 100%, respectively), or the 10 mg IRF group (80% and 80%). The rates of estrus (50%) and ovulation (50%) were intermediate in the 10 mg s.c. group. In summary, 25 mg of dinoprost injected into the IRF caused minimal behavioral or tissue response and induced luteolysis and fertile estrus. In addition, 10 mg of dinoprost injected into the IRF was as efficacious as 25 mg given either i.m. or into the IRF in inducing estrus and ovulation.