Similarly, Saito et al. [26] demonstrated that HS (41
°C for 12 h, 96 h after insemination [hpi]) significantly
decreased rates of blastocyst formation and blastocyst
hatching for both Holstein oocytes fertilized with Gir
(Bos indicus) semen and those fertilized with Holstein
semen. However, Eberhardt et al. [27] reported that
Nelore embryos were more resistant to HS than Holstein
or crossbred embryos during early in vitro development,
and that resistance to HS resulted from genetic
contributions of both the oocyte and sperm, because
oocytes from Holstein cows fertilized with Nelore semen
were significantly more resistant to HS (12 h, 96
hpi) than those fertilized with Angus semen. This assertion
was supported by data obtained by Pegorer et al.
[28] in which the use of Gir bulls increased the pregnancy
rate of lactating Holstein cows during the summer
when compared with Holstein bulls.