NO DIFFERENCE IN MATURATION CAPACITY, IN VITRO FERTILIZATION AND PREGNANT RATE OF OOCYTES OBTAINED BY ULTRASOUND-GUIDED OVUM PICK-UP FROM PREGNANT DAIRY COWS AND HEIFERS

Several lines of evidence assign to the ovarian follicular microenvironment the disparity between the fertility of dairy cows and heifers. This work evaluated the difference in maturation and subsequent embryonic development and pregnancy rate of oocytes from pregnant cows and heifers, during the spring season in a hot-desert weather location in Mexico. The oocytes were obtained from 112 ovum pickup technique (OPU) sessions, from Holstein pregnant cows, which were transported and maturated for 24 hoursusing a shipping and maturation commercial medium (SMM), fertilized and incubated in vitro (IVP-ET) evaluating number of oocytes obtained and embryoproduction. In the same way, oocytes obtained from 39 OPUsessions, from Holstein pregnant heifers, were exposed to the same protocol as the cows, and compared embryoproduction. Sexed frozen semen was used for both experiments. The 113 embryos obtained from cows and heifers were transferred, until reaching gestation diagnostic at day 45. Results showed significant differences in the number of oocytes obtained between cows of second and third lactation; however, no difference was shown among the number of embryos produced. While, for development of matured, fertilized and cultured oocytes, there was only significant difference in cows of second lactation, however, there was not an influence on the pregnancy rates. Although, the cleavage rate was higher for the group of heifers (63.5%), no difference was observed between groups. Also the pregnancy rate of transferred embryos, showed no difference between groups. We conclude that the number of recovered oocytes, the rate of cleavage, oocyte maturation and embryonic development through the OPU technique in pregnant dairy cattle are similar to what is obtained from pregnant heifer