CHARACTERISTICS OF OVULATIONS IN SUPEROVULATED CATTLE

The characteristics of ovulations in superovulated cattle were studied by means of frequent transrectal ultrasonographic examination of the ovaries prior to and during superovulation. Diary heifers and cows (n = 25) of mixed breeds were superovulated on Days 9-12 of the estrous c ycle (estrus designated Day 0) by an FSH/prostaglandin F2alpha (PGF) r egimen followed by inseminations at 60 and 72 h after the PGF injectio n. Transrectal ultrasonography of the ovaries was performed at 4 h int ervals starting at estrus until the estimated cessation of ovulation. The mean interval from PGF treatment to the onset of ovulation was 68. 6 +/- 1.3 h (range 60-84 h) and the ovulatory period lasted for 8.3 +/ - 0.5 h (range 4-12 h). The majority of ovulations occurred during the first 4 h of this period, independent of side (left vs. right ovary) or parity (heifers vs. cows). The onset of ovulation occurred later in animals with lower ovulation rates. The duration of the ovulatory per iod was proportional to the number of ovulations. In conclusion, ultra sonography may be used to monitor the occurrence of ovulations in supe rovulated cattle.