Blood levels of progesterone and 15-Keto-13, 14-dihydro prostaglandin F(2alpha) during the estrous cycle of oxytocin-treated cows.
Six non-lactating Holstein cows were injected with 230 iu oxytocin subcutaneously twice daily from days 2 through 6 of the cycle. Controls (n=6) were given saline injections using the same schedule. Blood samples were collected at frequent intervals before and after each saline or oxytocin injection. Progesterone and 15-Keto-13, 14-dihydro prostaglandin F(2alpha) (PGFM), the major metabolite of prostaglandin F(2alpha), were analysed by radio-immunoassay. Oxytocin injections significantly increased plasma prostaglandin concentrations on days 2 and 3 when compared with the controls. In two oxytocin-treated cows, the cycle was shortened to 10 and 12 days. Estrus was preceded by a PGF(2alpha) release very similar to that preceding spontaneous estrus. Two of the oxytocin-treated cows showed estrus on day 21 and 22 preceded by luteolytic release of PGF(2alpha). Two oxytocin-treated cows developed cystic corpora lutea and had not shown heat when the ovaries were removed four weeks later. All oxytocin-treated cows showed a slower progesterone increase through day 8 than the controls. The study shows that endocrine events preceding cycle alterations in oxytocin-treated cows involve release of PGF(2alpha) and lowered levels of progesterone.
Oyedipe
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Department of Theriogenology, College of Veterinary Medicine, University of Minnesota, St. Paul, MN. USA; Department of Obstetrics and Gynecology, and Clinical Chemistry, College of Veterinary Medicine, Swedish University of Agricultural Sciences, Uppsala, Sweden.
Gustafsson
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Kindahl
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