Effect of the ovulatory follicle diameter and progesterone concentration on the pregnancy rate of fixed-time inseminated lactating beef cows

The objective of this study was to evaluate the influence of the ovulatory follicle diameter on the reproductive performance of lactating beef cows subjected to low progesterone fixed-time artificial insemination (FTAI) protocols. Ninety-three lactating beef cows (60-80 days postpartum) at random stages of estrous cycle were given a luteolytic dose of prostaglandin F2α (500 μg cloprostenol; PGF) twice, 11 d apart. Ten days after the second PGF treatment, cows were given 1.5 mg of estradiol benzoate im and a progesterone-releasing intravaginal device (Cue-Mate) with a single pod containing 0.78 g progesterone (Day 0). Cows received another luteolytic dose of PGF on Day 0. On Day 8, the Cue-Mate was removed. Fifty-four to 56 hours later, cows received 12.5 mg of porcine LH (pLH) i.m. and were concurrently artificially inseminated. Ultrasound examinations of the ovaries were performed on Days 10 and 17 to evaluate the diameter of ovulatory follicle and corpus luteum, respectively. Cows which presented ovulatory follicle > 19 mm resulted in larger corpus luteum than cows that had ovulatory follicle