Integrative effects of long-acting progesterone and micronutrient-amino acid complex on pregnancy maintenance in Bos indicus females under field conditions

The present study aimed to evaluate the pregnancy rate following fixed-time artificial insemination (FTAI) in Nelore cattle supplemented with either long-acting progesterone (Experiment 1) or an injectable nutritional complex (Experiment 2). In Experiment 1, multiparous cows underwent estrus synchronization and were inseminated on day D10 (D0 = first day of synchronization). On D15, animals were assigned to a control group (n = 166), which received an intramuscular injection of 0.5 mL of 0.9% NaCl solution, or to a treated group (n = 147), which received 0.5 mL of long-acting progesterone (150 mg). In Experiment 2, heifers were divided into a control group (n = 108), which received no treatment, and a treated group (n = 99), which received an intramuscular injection of a nutritional supplement on D0 of synchronization. After 7 days of FTAI, all cows and heifers were maintained with bulls for natural mating (20 females per bull) for the following 45 days. Pregnancy diagnosis was performed 70 days after FTAI. The pregnancy rate was higher in the treated groups for both experiments (53.1% vs. 42.8% in Experiment 1, and 53.7% vs. 38.8% in Experiment 2), although differences were not statistically significant (p > 0.05). In animals that did not conceive, ovarian cyclicity was not suppressed, indicating that the use of long-acting progesterone or nutritional supplementation did not interfere with the return to estrus. In conclusion, supplementation with long-acting progesterone or an injectable nutritional complex tended to improve pregnancy rates in Nelore cattle subjected to FTAI, without residual inhibitory effects on subsequent ovarian activity.