Factors affecting the success of superovulation and embryo recovery were examined in two groups of 16 lactating Friesian cows which were superovulated twice at five to six week intervals in a 24 factorial experiment. There were no differences in ovarian response using pregnant mare serum gonadotrophin or human menopausal gonadotrophin. A total of 3000 iu human chorionic gonadotrophin given intravenously at the first insemination significantly (P less than 0.01) affected embryo recovery rate. A single intramuscular treatment with releasing hormone had no effect. A lower proportion of unfertilised eggs was recovered after insemination with semen from a bull of above average fertility than with semen from a bull of below average fertility (P less than 0.03). Insemination routines affected both the proportion of unfertilised eggs (P = 0.06) and embryo recovery rate (P less than 0.03). Antibacterial treatment given when insemination was carried out after the end of oestrus did not affect success. The three-way circulation system of embryo and fluid recovery was significantly (P less than 0.01) more efficient than the two-way to-and-fro system at day 7 after oestrus, but this appeared to alter at day 8 in favour of the two-way system. A more efficient fluid recovery was achieved with the three-way system (P less than 0.001). Catheter location, catheter size, interval from calving and condition of the donor did not affect success, but embryo recovery rate from younger cows (less than 4.5 years) was lower than from older animals (4.5 to 7 years) (P less than 0.05).
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