Resistance of embryos from Bos indicus cattle during early stages of in vitro development to heat shock compared to embryos crossbred from crossbred cattle
F.M. Monteiro, E.C. Freitas, D.S. Melo, L.M. Carvalho, A.B. Teixeira, L.A. Coelho, L.A. Trinca, C.M. Barros
Anim Reprod, vol.4, n1, p.51-58, 2007
There is evidence that the detrimental effects of heat stress on fertility are less pronounced in heattolerant breeds, due primarily to differences in thermoregulation. The current objective was to test the hypothesis that Nelore embryos (Bos indicus, I) at early stages of in vitro development are more resistant to heat shock than those from Bos taurus (T) oocytes fertilized with Nelore spermatozoa (crossbred taurus embryos, IT) or oocytes from crossbred animals (Nelore x taurus) fertilized with Nelore spermatozoa (crossbred indicus embryos, ITI). Embryos carrying different genotypes were exposed to a control temperature of 39°C continuously or heat shock of 41°C for 9 or 12 h at 12, 48, or 80 hours post-insemination (hpi) and 39°C thereafter. Overall exposure to 9 or 12 h heat shock at 12, 48 or 80 hpi did not affect cleavage rate in Nelore (I), Nelore vs crossbred (ITI), and Nelore vs Bos taurus (IT). For embryos exposed to 9 or 12 h heat shock at 12 hpi, the number of oocytes that developed to the blastocyst stage (blastocyst/oocyte) at Day 8 was: I (45/94, 47.9% at 39°C; 47/117, 40.2% at 41°C/9h; 43/115, 37.4% at 41°C/12h; P > 0.05) vs. ITI (69/150, 46%; 85/172, 49.4%; 48/164, 29.3%, respectively; P < 0.05); I (48/118, 40.7% at 39°C; 33/80, 41.2% at 41°C/12h; P > 0.05) vs. IT (34/68, 50%; 17/72, 23.6%, respectively; P < 0.05). The detrimental effect of heat shock on the Nelore breed was noted only when Nelore data at 12 hpi were pooled in a single dataset (140/269, 56.7% at 39°C; 89/209, 42.6% at 41°C/9h; 115/262, 43.9% at 41°C/12h; P < 0.05). For Nelore (I), crossbred (ITI), or Bos taurus (T) oocytes submitted to heat shock 48 or 80 hpi during 12h, there was no significant decrease in cleavage or blastocyst rates. However, oocytes from Bos taurus cows produced fewer blastocysts than those from Bos indicus cows (P < 0.05). In conclusion, the results of this study indicate that Nelore embryos at an early stage of in vitro development are more resistant to heat shock than those from Bos taurus oocytes fertilized with Nelore spermatozoa. However, the resistance of Nelore embryos to heat shock was similar to those embryos from crossbred oocytes fertilized with Nelore spermatozoa.
Bos indicus, pre-implantation embryo, heat shock, crossbred, genotype