Resumen:
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
heifers