Luteolytic potency in a novel prostaglandin analogue

Estrus induction in cycling sows with exogenous prostaglandin is hindered by the extended refractory period and resistance of swine to the luteolytic action of PG's. The luteolytic potency of a novel PGF2 alpha analogue, Schering ZK 71677, was assessed at four different dosages in chronically cannulated cycling swine. Dosages totalling 1, 1.5, 3 and 10 mg of ZK 71677 were split into two injections given intramuscularly on day 13 of the estrous cycle. Onset of behavioural estrus and serum levels of progesterone and PGF metabolite were monitored. The three lowest doses did not advance estrus but did cause a transitory decline in serum progesterone concentration on day 13. The 10 mg level advanced estrus in three of four sows although the overall mean cycle length did not differ from pretreatment cycles (18.5 +/- 1.3 vs 21.3 +/- 0.6 days). Progesterone values dropped steadily in all four sows in the 10 mg treatment group. No level of ZK 71677 affected serum levels of PGF metabolite. The highest level tested of PGF2 alpha analogue ZK 71677 elicited an uninterrupted decline in serum progesterone concentrations but was inconsistent in its ability to promote early onset of behavioural estrus in swine.