The probability of a pregnancy decreases substantially in lactating dairy cows treated with Ovsynch if corpus luteum regression is delayed or incomplete. There are two PGF2α products approved in the USA for luteolysis, dinoprost tromethamine and cloprostenol sodium. Cloprostenol has a longer half-life compared to dinoprost because it is more resistant to endogenous metabolism. In this thesis, we hypothesized that cloprostenol would reduce the time to complete luteolysis and increase conception rates compared to dinoprost because of differences in half-life. In the studies presented in Chapter 2, the decline in circulating P4 was accelerated between 0 and 12 h post-injection for cows treated with cloprostenol vs. dinoprost , but not at 24, 36 and 48 h. Serum concentrations of E2 were greater in cloprostenol vs. dinoprost treated cows 48 h following treatment. In studies presented in Chapter 3, there was no difference in conception rates, rate of luteolysis or concentrations of estradiol between cows treated with cloprostenol vs. dinoprost. Serum concentrations of progesterone at time of PGF2α was positively related with predicted probability of a pregnancy and with predicted probability of luteolysis. In summary, cloprostenol induced a greater decrease in P4 for the first 12 h following treatment and subsequently a greater increase in E2 compared to dinoprost, although there were no differences in these two products in conception rates, % of cows with complete luteolysis, and pregnancy loss.
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