HIGH ENVIRONMENTAL-TEMPERATURE AND HUMIDITY DECREASE OOCYTE QUALITY IN BOS-TAURUS BUT NOT IN BOS-INDICUS COWS

Two experiments were conducted to assess the effects of environmental temperature and humidity on the quality and developmental capabilities of bovine oocytes. In Experiment 1, Bos taurus (Holstein and crossbre d Angus) cows were subjected to 5 weekly sessions of ultrasound-guided follicle aspiration from February 16 through March 23 (cool season) a nd 5 sessions from May 22 through June 20 (hot season). In Experiment 2, Bos taurus (Holstein) and Bos indicus (Brahman) cows were superstim ulated (Super-Ov(R)) during the months of August (hot season) or Janua ry (cool season), and each cow was subjected to a single oocyte aspira tion session. In each experiment, oocytes were classified as normal or abnormal based on ooplasm morphology and cumulus cell layers. In Expe riment 1, oocytes classified as normal were in vitro matured and ferti lized (IVM/IVF), and the resulting embryos cultured for 8 d. All oocyt es recovered from superstimulated cows in Experiment 2 were matured an d fertilized in vitro and the subsequent embryos cultured for 8 d, reg ardless of their morphological appearance. In Experiment 1, Bos taurus cows produced a higher (P = 0.02) percentage of normal oocytes during the cool season (75.9 +/- 8.0) than during the hot season (41.0 +/- 9 .5). The percentage of fertilized oocytes developing to the 2-cell (82 .4), 8-cell (65.4) and morula (46.6) stages were also greater (P less than or equal to 0.06) during the cool season than the hot season (45. 0, 21.2, 6.0 for 2-cell, 8-cell and morula stages, respectively). In E xperiment 2, Bos taurus cows (Holstein) had a lower (P = 0.01) percent age of normal oocytes in the hot season (24.5 vs 80.0) and a lower (P less than or equal to 0.003) percentage of fertilized oocytes developi ng to the 8-cell, morula and blastocyst stages. No difference (P great er than or equal to 0.57) in the percentage of normal oocytes or in em bryo development was detected between seasons in Bos indicus (Brahman) cows. In conclusion, high environmental temperature and humidity resu lted in a marked decline in the quality of oocytes retrieved from Bos taurus cows and markedly decreased their in vitro developmental capabi lities. In contrast, a high percentage of oocytes retrieved from Bos i ndicus cows exhibited normal morphology and yielded a high proportion of blastocysts, regardless of season. (C) 1998 by Elsevier Science Inc .