|Krininger iii, C.|
|Chase, Chadwick - Chad|
Submitted to: Animal Reproduction Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/17/2003
Publication Date: 11/10/2003
Citation: Krininger Iii, C.E., Block, J., Al-Katanani, Y.M., Chase, C.C., Hansen, P.J. Differences between brahman and holstein cows in response to estrus synchronization, superovulation and resistance of embryos to heat shock. Animal Reproduction Sciences:Vol 78,pp 13-24 (2003). Interpretive Summary: Reproductive rates are extremely low during the hot summer months particularly for unadapted cattle. Tropically-adapted cattle are less likely to undergo hyperthermia in response to heat stress than non-adapted cattle. At the cellular level, Brahman (tropically-adapted) cells (endometrium and white blood cells) were more resistant to elevated temperature than cells from non-adapted cattle. Furthermore, when 9-16 cell embryos were fertilized in the lab and subsequently heat shocked, development of Brahman embryos was less inhibited than Angus or Holstein embryos. Others have suggested that, in cattle, the embryo's genome is not fully activated until the 8-16 cell stage. Thus, it is possible that the genetic effects on embryonic resistance to elevated temperature are not seen at stages of development before the 8-16 cell stage. Therefore, the present study was designed to determine if Brahman embryos have greater resistance to heat shock than Holstein embryos at a stage in development before the embryo's genome is fully activated. Results showed that the genetic effects on tolerance of cells (embryo) to heat shock that make Brahman embryos more resistant to heat shock are not expressed at the 2-4 cell stage. Embryo cleavage tended to occur earlier in Brahman than Holstein embryos suggesting that breed differences in timing of ovulation, fertilization, or events leading to cleavage. This implies that very early embryos are susceptible to heat stress even when the genetics of the dam are tropically-adapted.
Technical Abstract: Embryos from Bos indicus are more resistant to elevated culture temperature (i.e. heat shock) than embryos from some Bos taurus breeds. The present experiment was designed to determine if Brahman embryos have greater resistance to heat shock than Holstein embryos at a stage in development before the embryonic genome was fully activated. A second objective was to test breed effects on estrus synchronization and superovulation responses. A total of 29 Brahman and 24 Holstein cows were subjected to estrus synchronization using gonadotropin releasing hormone (GnRH) and prostaglandin F2a (PGF2a). Embryos were collected at 48 h and day 5 after insemination. There was a tendency for a lower proportion of Brahmans to be detected in standing estrus than Holsteins. There were no differences between breeds in the proportion of cows detected in estrus using both tail paint and standing estrus as criteria or in interval from PGF2a to estrus. The degree of synchrony in estrus was greater for Brahmans. Superovulation response was generally similar between breeds. At 48 h after insemination, there was a tendency for a greater proportion of Brahman oocytes to have undergone cleavage. Uncleaved oocytes were cultured for an additional 24 h - at this time, cleavage rate was similar between breeds. When embryos reached the 2-4 cell stage, they were heat-shocked for 4.5 h at 41 C. This heat shock reduced the proportion of embryos that developed to the blastocyst stage but there was no breed x treatment interaction. At day 5 after insemination, the number of embryos recovered was too low to allow comparison of breed effects. In conclusion, genetic effects on cellular thermotolerance that make Brahman embryos more resistant to heat shock are not expressed at the 2-4 cell stage. There were few differences between Brahman and Holstein in response to estrus synchronization and superovulation. The fact that cleavage tended to occur earlier in Brahman than Holstein embryos suggests breed differences in timing of ovulation, fertilization or events leading to cleavage.