Effect of insemination regimen on embryo production in superovulated cows.

Three experiments tested the effects of six insemination regimens on embryo production in superovulated cows. One, two or three inseminations with one unit of semen at each time produced the same percentage fertilised (74, 68 and 74 per cent, P = 0.673) and the same number of fertilised embryos (8.2, 6.3 and 9.1, P = 0.136). However, the one and two inseminations group had less transferable (P = 0.008) and total (P = 0.051) embryos (3.9/9.6 and 3.9/8.9) than the three inseminations group (6.8/13.2). The percentage transferable remained the same (42, 45 and 58 per cent, P = 0.161). When two units of semen were used at the first or middle insemination and one, two and three inseminations were compared, the percentage fertilised (65, 77 and 77 per cent, P = 0.082) and the number fertilised (7.0, 7.4 and 8.6, P = 0.565) were again the same but the number (P = 0.047) and percentage transferable (P = 0.000) increased between the one and two inseminations (3.8 vs 5.7 and 30 per cent vs 54 per cent). The increase in transferable embryos with multiple inseminations could not be explained physiologically, but is of concern since transferable embryos are the "sales product' of superovulation. Two inseminations with one unit of semen was as effective as two inseminations with three units of semen, in terms of percentage fertilised (68 and 70 per cent, P = 0.762), number fertilised (10.3 and 8.3, P = 0.582), transferable embryos (6.7 and 5.7 P = 0.532), percentage transferable (44 and 46 per cent, P = 0.737) and total embryos recovered (14.8 and 12.7, P = 0.54).(ABSTRACT TRUNCATED AT 250 WORDS)