Desempenho reprodutivo de novilhas, vacas desmamadas e vacas amamentando submetidas ao protocolo de inseminação com detecção de estro e em tempo fixo (IAETF), seguido de ressincronização

Abstract

The aim of this study was to compare the reproductive performance of heifers, nonlactating and lactating beef cows submitted to fixed time and estrus detection artificial insemination hormonal protocol (FTEAI). A total of 382 bovine females divided in 136 heifers, 103 nonlactating and 143 lactating cows (between 40 and 70 days postpartum) were used. On day 0 all animals received an intravaginal device containing 1.2g of progesterone (used on adult cows) or reutilized (used on heifers synchronization and on heifers and adult cows resynchronization) and an injection (IM) containing 2 mg of estradiol benzoate (EB). In the afternoon of day 6, animals received an injection (IM) containing 300 IU of equine chorionic gonadotropin (eCG) and 0.15 mg of D-cloprostenol and calves a no se tablet for 4 days (until day 10). In the afternoon of day 7, intravaginal devices were removed and estrus was monitored at 24 and 36 h after device removal. Animals detected in estrus were artidicial insemination (AI) 12 h later and the remaining received an injection (IM) containing 0.01mg of Busereline Acetate at 48 h after device removal and were submitted to timed artificial insemination (TAI) 12 to 16 h after the injection (Day 10). In the synchronization, estrus rate differ (P < 0.05) among the three categories (63.1%, 52.9% and 24.4% to nonlactating cows, heifers, and lactating cows, respectively). Where as in resynchronization, only lactating cows showed lower (P < 0.05) estrus rate (25.0%) when compared for heifers (82.0%) and nonlactating cows (72.7%). In the synchronization heifers showed higher (P < 0.05) pregnancy rate (71.3%) than lactating cows (58.0%), but both categories did not differ (P > 0.05) in relation to nonlactating cows (67.9%). In resynchronization, pregnancy rate of three 8 categories did not differ betwem (P > 0.05) each other (51.2%, 51.5% and 60.0% for heifers, nonlactating cows and lactating cows, respectively). The cumulative pregnancy rates from two FTEAI (86.0%, 84.4% and 83.2% for heifers, nonlactating and lactating cows, respectively) and from final reproductive season after breeding with bulls (94.1%, 91.2% and 87.4% to heifers, nonlactating and lactating cows, respectively) did not differ (P > 0.05) among the categories. In conclusion, heifers, nonlactating and lactating cows show similar reproductive performance at the end of breeding season when submitted to resynchronization using FTEAI, as well as after a short-term breeding with bulls.