Efeito de diferentes combinações hormonais sobre a taxa de retorno ao cio e prenhez em vacas de corte lactando, submetidas a inseminação artificial em tempo fixo

Abstract

The synchronizing protocols of estrus and ovulation in cattle herds aim at eliminating problems in IA and promoting a quick return to the cycle of cows in lactation, however a good reproductive performance depends on the nutritional state of the herds. The aim of this study was to evaluate the effect of the GnRH (post-IA) hormone and the association of eCG (pre-IA) and GnRH (post-IA) to the conception rate in lactating beef cows, submitted to an insemination protocol at a fixed time. Two hundred and eighteen crossbred cows, predominating zebu and British breeds, where 65% presented CC<3, were synchronized. The treatments used were: Control (C n=55), day 0 (D0) = intra-vaginal beads made of polyurethane with 250 mg of medroxyprogesterone acetate, 2 mg of estradiol Benzoate (BE) intramuscular (IM), day 8 (D8) removal of the beads plus 12,5 µg of Cloprostenol IM, and day 9 (D9) 1 mg of BE; Treatment eCG (TE n=55): identical to C1 plus 400 UI of eCG in D8; Treatment GnRH (TG n=56): identical to C1 plus one dose of 25 µg of Lecirelina 7 days after the pre-fixed insemination; Treatment eCG+GnRH (TEG, n=55): identical to TE plus one dose of 25 µg of Lecirelina 7 days after the pre-fixed insemination. All animals were inseminated 47 hours after removal of the beads (D10). The animals were monitored 17 to 23 days after the insemination at a fixed time (IATF) to determine the return rate. The gestation diagnostic was carried out 40 days after IATF with a transrectal linear transducer (5Mhz, Aloka). The synchronized pregnancy rate was 4.6% (10 out of 218) and the return rate was 8.7%, not differing between treatments (p>0,05). It is concluded that the treatments had no effect on the pregnancy rate in lactating beef cows inseminated at a fixed time.