Effect of Different Prostaglandin Treatment Protocols on Luteolysis and Ovulation in Dairy Cows

Abstract

During the past 25 years, several methods were developed to synchronize estrus in dairy cattle. Synchronization with prostaglandin F2α (PGF2α) is successful when cows are bred at a detected estrus because estrus detection rates and artificial insemination (Al) are more efficient than daily detection of estrus (Stevenson and Pursley, 1994). The success of estrous induction with PGF2α depends on the presence of a functional corpus luteum (CL). In case of a palpable CL, Archbald et al (1994) found that the percentage of milking cows observed in estrus within seven days after treatment (25 mg of PGF2α) was 55% (61/111). This management tool still does not control the time of AI, because estrus detection continues to be necessary, which is evidenced by the lower pregnancy rate after timed AI compared with AI after detected estrus. This might be partially explained by the variation in time of ovulation over periods of five days with respect to time of AI (Stevenson et al, 1987). Various attempts have been made to overcome this variability in response to PGF2α treatments. The administration of other hormones in conjunction with PGF2α, such as progesterone, estradiol benzoate, human chorionic gonadotropin (hCG) and gonadotropin releasing hormone (GnRH) (Deletang 1975; De Rensis and Peter 1999; Pursley et al, 1996), have been attempted. There was a better degree of synchronization but the pregnancy rate was similar to that of untreated cows. Similarly, two prostaglandin injections at an eight-hour interval was more effective on the incidence of luteolysis than a single injection (Archbald et al, 1993). There are several studies dealing with the effect of prostaglandin on the area changes of corpus luteum and follicles in heifers (Kastellic and Ginther 1991), on corpus luteum size and plasma progesterone concentrations in cattle (Assey et al, 1993), and the effect of different doses of PGF2α on fertility (Lagar 1977), however the effect of different doses of PGF2α on the area changes of the corpus luteum, the largest follicle and the progesterone (P4) concentration has not been examined. The objective of our study was to compare the effect of different doses of PGF2α (first trial-0 mg, 25 mg, 35 mg; second trial-2 x PGF2α treatment at an eight-hour interval) on the corpus luteum, the largest follicle and the progesterone concentration in dairy cattle. The time to ovulation after AI in PGF2α-treated and untreated cows (third trial) was also determined.