The effect of a double dose of cloprostenol sodium on luteal blood flow and pregnancy rates per artificial insemination in lactating dairy cows.

Inadequate luteolysis in fertility programs is a problem for lactating dairy cows treated with a single dose of PGF. The proportion of cows with complete luteolysis can be increased by administering 2 doses of PGF 24 h apart. This study hypothesized that a double dose of cloprostenol sodium (1.0 mg) could take the place of 2 doses 24 h apart due to its enhanced half-life. Cows were allocated to receive 1 of 3 treatments: negative controls: 0.5 mg of cloprostenol sodium (single; n = 337); positive controls: two 0.5-mg doses of cloprostenol sodium 24 h apart (two/24; n = 313); and treated: 1.0 mg of cloprostenol sodium (double; n = 298) at the final PGF of Double-Ovsynch. Cows received artificial insemination (AI) 16 h after final GnRH of Double-Ovsynch. Pregnancy diagnosis was determined at 24, 34, 62, and 184 d post-AI. Pregnancy loss was categorized in the following periods: between 24 to 34, 34 to 62, and 62 to 184 d post-AI. Ultrasonography (B-mode and color Doppler) was used to assess luteal function pre- and posttreatment with various doses of cloprostenol sodium. Luteal volume and luteal blood flow (LBF) from d 7 and 14 corpora lutea were determined before treatment (d -1), and 2 and 4 d after treatment. No evidence was observed of an effect of treatment on pregnancy rates per AI at 24, 34, or 62 d post-AI. No effect was observed of treatment on pregnancy losses occurring between d 24 and 34, 34, and 62, and between 62 and 184 d post-AI. However, third-plus parity cows treated with the single treatment had greater pregnancy loss compared with two/24 and double between d 24 and 34 post-AI. Third-plus parity cows that received the double treatment had lower LBF 2 and 4 d after treatment compared with cows treated with single. Amount of LBF present 4 d after treatment was not a predictor of pregnancy or pregnancy loss. A double dose (1.0 mg) of cloprostenol sodium may be a feasible alternative for fertility programs based on nondifferent outcomes to the two/24 treatment, lower pregnancy losses, and reduced LBF disappearance following treatment in third-plus parity cows in comparison with the single treatment.