The effect of time of artificial insemination on fertilization status and embryo quality in superovulated cows

Thirty nonlactating Holstein cows were superovulated to determine the effec t of artificial insemination time on fertilization status and embryo qualit y. During the luteal phase of the estrous cycle, cows were administered 38 mg FSH-P in a 4-d descending dose regimen. Luteolysis was induced with two injections of prostaglandin on the last day of FSH-P treatment. All cows we re continuously monitored for behavioral estrus using the HeatWatch estrus detection system. All cows were inseminated once with one .5 mL straw (50 x 10(6) sperm) at either 0 (n = 10), 12 (n = 10), or 24 h (n = 10) after the first standing event. The elapsed time (mean +/- SD) from the first prosta glandin dose to the first standing event was 39.4 h +/- 7.7 h. The (mean +/ - SD) duration of behavioral estrus was 13.2 h +/- 4.1 h. The (mean +/- SD) number of standing events war; 27 +/- 17. Five hundred twenty-nine embryos and ova were recovered nonsurgically 6 d after insemination. Fertilization rates were 29 (0 h), 60 (12 h), and 81% (24 h) (P < .01). Percentages of e xcellent and good, fair and poor, and degenerate embryos were not different (P > .05). Percentages of embryos with accessory sperm were 5 (0 h), 8 (12 h), and 41 (24 h) and differed between the 0 and 24 h and the 12 and 24 h inseminations (P < .01). Artificial insemination of superovulated, nonlacta ting Holstein cattle 24 h after onset of estrus increased fertilization rat e and percentage of embryos with accessory sperm compared with insemination at 0 or 12 h after onset of estrus. Embryo quality was not affected by tim e of insemination.