EFFECT OF DELAYED SUPPLEMENTATION OF FETAL CALF SERUM TO CULTURE-MEDIUM ON BOVINE EMBRYO DEVELOPMENT IN-VITRO AND FOLLOWING TRANSFER

Supplementation of synthetic oviduct fluid (SOF) medium plus amino aci ds and bovine serum albumin (BSA) with either fetal calf serum (FCS) o r charcoal-treated FCS (CT-FCS) from Day 5 of development was investig ated to determine if either in vitro or post-transfer development was altered. Development to the compact morula stage or beyond was similar for all 3 treatments. However, blastocyst development at Day 7 was ac celerated when serum was added to the medium (21.6, 40.1 and 39.4% bla stocysts from cleaved embryos for BSA, FCS and CT-FCS, respectively; P <0.01), but cell number of the resulting embryos was unaffected. Furth ermore, addition of CT-FCS decreased the between replicate variation i n embryo development and produced more Grade 1 and 2 quality embryos ( 25.8%) than BSA supplementation (18.1%; P<0.05). The transfer of Grade 1 and 2 embryos at Day 7 following culture resulted in similar pregna ncy and embryo survival rates for the 3 treatments, with a tendency fo r lower embryo survival of embryos cultured in FCS (embryo survival at Day 50 = 37.7% vs 53.3% and 57.6% for FCS, BSA and CT-FCS, respective ly; P approximate to 0.1). Significant fetal loss from Day 50 to term occurred within all 3 treatments. There were no birth weight differenc es for calves amongst the 3 culture treatments; however, one of the si res produced calves that were significantly heavier than expected, sug gesting a possible sire-by-embryo interaction. These results demonstra te that addition of FCS may promote blastocyst development; however, t here was also a tendency for lower embryo survival. Thus charcoal trea tment of FCS is recommended, because it decreases variability in embry o development between runs and results in embryo survival rates to ter m similar to that of BSA-supplemented media. (C) 1998 by Elsevier Scie nce Inc.