Produção in vivo e transferência de embriões F1 em rebanhos leiteiros, utilizando-se cruzamento recíproco entre as raças Holandês e Gir, em duas épocas do ano.

Abstract

It was evaluated embryo production from reciprocal matting of Holstein and Gyrbreeds, and the use of crossbreed recipients, in summer or winter. Holstein (7 in eachseason), and Gyr females (7 in summer and 5 in winter) were superovulated. Embryos(grade 1 and 2), were frozen for further in vitro culture or inovulation. The recipients(49 cyclic or noncyclic heifers and 54 noncyclic F1 cows - 21 to 65 days post partumweresynchronized with protocols associating progesterone and estradiol. Eighty-sevenF1 embryos (grade 1) were transferred and 72 (grades 1 and 2) were cultured in vitro for72h. Total ova/embryo recovered, viable and freezable embryos means were,respectively, 20.1, 14.6 and 13.3 in winter and 8.6, 7.1 and 6.6 in summer (p>0,05) forHolstein and 2.4, 1.6 e 1.4 in winter and 7.7, 6.8 and 4.7 in summer, for Gyr donors.Synchronization rates were different between cyclic (93.9%) or noncyclic (62.5%)heifers (no season effect) and, for cows, 81.8% in summer and 93.75% in winter(p>0.05). The DF size in the beginning of protocol was higher in that cows that hadovulated (13.1 mm x 10.6 mm; p<0.05). Pregnancy rates (days 30 and 60, respectively)were 41.0% and 33.3% for heifers and 14.6% and 12.5% for cows (p<0.05, comparingcows and heifers) not being affected by season. In vitro culture showed 46.3% and16.1% viability, and 26.8 and 3.2% hatching rates, for grades 1 and 2, respectively(p<0.05). Season did not affect embryo production from Holstein and Gyr donors andthe synchronization and pregnancy rates. Synchronization was affected by the CLpresence (in heifers) or the DF diameter (in cows) during the beginning of protocol