The influence of the addition of propylene glycol or monensin to diets of dairy cows during the transition period on return to ovarian cyclicity was evaluated. Forty two multiparous Holstein cows with an average milk production of 8,000kg were distributed in a split-plot design and were divided into groups receiving either control diets or diets increased with 30ppm of monensin or 300ml of propylene glycol during the transition period. Ovaries were evaluated by ultrasonography between days 4 and 46 post-partum. On days 10, 20, 25, 30, 35, 40, and 45 post-partum, blood samples were taken to assay progesterone. The addition of propylene glycol showed to be more efficient in accelerate the return to cyclic ovarian activity. Cows that received propylene glycol just during pre-partum, post-partum or during the hole transition period showed intervals from parturition to first ovulation of 29.0, 44.0 and 27.2 days, respectively. The intervals from parturition to conception for the same groups were 98.3, 90.8, and 100.0 days, respectively. The addition of monensin to diets did not show positive effects on post-partum return to ovarian cyclicity. Cows that received monensin just during pre-partum, post-partum or during the hole transition period showed intervals from parturition to first ovulation of 43.6, 39.3, and 42.8 days, respectively. The interval from parturition to conception for cows that received monensin pre and post-partum were 173.2 and 126.1 days, respectively.
dairy cow; follicular dynamics; progesterone; reproductive performance