|Hernandez-Ceron, J. - UNIVERSITY OF MEXICO|
|Hansen, P. - UNIVERSITY OF FLORIDA|
Submitted to: Journal of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: January 1, 2004
Publication Date: February 1, 2004
Citation: Hernandez-Ceron, J., Chase, C.C., Hansen, P.J. Differences in sensitivity to heat-shock between preimplantation embryos from heat-tolerant (brahman and romosinuano) and heat-sensitive(angus)breeds. Journal of Animal Science: Vol. 81, Suppl. 1 / Journal of Dairy Science Vol. 86, Suppl. 1. Technical Abstract: Certain heat-tolerant breeds of cattle have acquired mechanisms to protect cells against damage from high temperature. Exposure of embryos to 41 C reduced development more for Holstein and Angus (An) embryos than for Brahman (Br) embryos. The Romosinuano (Ro) is a Bos taurus from Colombia. Like Br, Ro is a tropically-adapted breed. It is not known, however, whether this breed, distinct in origin from Br, has evolved to possess cellular adaptations to heat shock. A study was performed to test whether Br and Ro embryos survive heat-shock better than An embryos. Cows (n=14 An, 17 Br, and 15 Ro) were slaughtered in groups of 2-3 per breed (5-6 replicates). For each replicate, ovaries were pooled within breed and oocytes harvested and fertilized with semen from a pair of bulls of the same breed. A different pair of bulls was used for each replicate. At d 4 after fertilization, embryos (at least 8 cells) were randomly assigned to control (38.5 C) or heat shock (41 C for 6 h) treatments. Development to blastocyst was determined on d 8. The proportion of oocytes that cleaved at d 4 tended to be highest for Ro (54, 50, and 70% for An, Br, and Ro). The proportion of cleaved embryos that were at least 8 cells at d 4 was lowest for Br (76, 55, and 77% for An, Br, and Ro). Heat shock caused a reduction in the proportion of embryos that became blastocysts at d 8. At 38.5 C, there were no significant differences in development among breeds. Among embryos exposed to 41 C, however, development was lower for An than for Br and Ro. Furthermore, there was a trend for an An vs (BR + Ro) x temperature interaction because heat shock reduced development more for An (30.3% at 38.5 C vs 4.9% at 41 C) than for Br 25.1 vs 13.6%) and Ro (28.3 vs 17.5%). There were no effects on cell number of d 8 blastocysts. Results demonstrate that embryos from thermotolerant breeds (Br and Ro) are more resistant to elevated temperature than embryos from a thermosensitive breed (An). Thus, the process of adaptation of Br and Ro breeds to hot environments resulted in both cases in selection of genes controlling thermotolerance at the cellular level.