7 ARTIFICIAL INSEMINATION IN BOS INDICUS WITH SEMEN IN SIMULTANEOUS POOL OF MULTIPLE BULLS

Abstract

The duration of spermatic viability in the female reproductive system in cattle is 18 to 24 hours. Therefore, the time required for sperm capacitation in different bulls demonstrated to be highly variable and may affect the adequate amount of capacitated sperm within an optimal window of time for fertilization. The aim of this study was to evaluate the conception rate in Nelore cows inseminated with semen from a single bull compared with semen from a pool of 3 bulls (Fertility Plus^®, ABS Pecplan, Minas Gerais, Brazil). On a random day of the estrous cycle (Day 0), 400 Nelore multiparous cows received a progesterone intravaginal device (1 g of P4, DIB^®, Intervet/Schering-Plough, Cotia, Brazil) plus 2mg of estradiol benzoate (i.m. Estrogin^®, Farmavet, São Paulo, Brazil). At the time of P4 device withdrawal (Day 8), 150 (ig of d-cloprostenol (i.m. Preloban^®, Intervet/Schering-Plough), 1 mg of estradiol cypionate (i.m. ECP^®, Pfizer, Brazil), and 300IU of eCG (i.m. Folligon^®, Intervet/Schering-Plough) were administered. At 48 to 52 h after implant removal, all cows were fixed-time inseminated (FTAI). Then, cows were homogeneously distributed based on the semen used for FTAI in 4 groups: CONV1 (conventional dose of semen from bull 1), CONV2 (conventional dose of semen from bull 2), CONV3 (conventional dose of semen from bull 3), FERT (pool of semen from bulls 1, 2 and 3 homogeneously mixed in a single dose). Both conventional and Fertility Plus batches of semen contained a total dose of 30 × 10⁶ spermatozoa. For pregnancy diagnosis, an ultrasonographic (CHISON 500VET, USP Brasil Eletromedicina, São Paulo, Brazil) examination was performed 30 days after the FTAI. Data were analyzed using the GENMOD procedure of SAS (SAS Institute, Cary, NC, USA). There was no interaction between treatment and body condition score [using a 1 (very thin) to 5 (very fat) point scale] or AI technician. The conception rates for CONV1, CONV2, CONV3, and FERT were, respectively, 40/101 (39.6%)^b, 50/99 (50.5%)^ab, 46/99 (46.5%)^ab, 54/101 (53.5%)^a; P < 0.05. In addition, the mean of conventional v. Fertility Plus treatments presented conception rates of 136/299 (45.5%) v. 54/101 (53.5%), respectively (P = 0.14). No significant statistical differences were observed between treatments. However, this trial showed that the utilization of the new Fertility Plus technology increased the overall conception rate by 8.0%. This probably implicates a complementary effect among semen samples and provides a greater time of sperm viability in oviduct. Also it provides evidence of the individual variation in capacitation time of bulls used for composition of the pool. Pooled semen of multiple sires may improve the reproductive performance at AI in cattle and increase the potential of the beef industry to produce pregnancies and born calves.