Proceedings of the 5th International Symposium on EQUINE ...

Havemeyer Foundation Monograph Series No. 3TABLE 1: Embryo recovery rates from mares following ovulation <strong>of</strong> non-echogenic or echogenicpreovulatory folliclesUltrasound appearance (N) No. <strong>of</strong> cycles No. <strong>of</strong> embryos % embryo recoveryNonechogenic 34 111 50 45.0Echogenic 34 44 92 0.5ovulation when a preovulatory follicle greater than35 mm was detected. Mares were inseminatedwith ei<strong>the</strong>r fresh, cooled-transported or frozensemen prior to ovulation. A mare was consideredto be pregnant following breeding to an echogenicor nonechogenic follicle if ei<strong>the</strong>r an embryo wascollected 7–8 days after ovulation or an embryonicvesicle was detected by transrectalultrasonography 12–16 days after ovulation.Statistical comparison <strong>of</strong> pregnancy ratesbetween mares that ovulated ei<strong>the</strong>r echogenic ornonechogenic follicles was made by Chi-squareanalysis. Comparison <strong>of</strong> ages <strong>of</strong> mares with andwithout echogenic ovulatory follicles was madeby Student’s t-test. Data are presented as <strong>the</strong> mean±sd.RESULTSRecords for 1,694 oestrous cycles from a total <strong>of</strong>721 mares examined during <strong>the</strong> 5 year period werereviewed. Non-echogenic and echogenicpreovulatory follicles were noted in 1,589 (93.8%)and 105 (6.2%) <strong>of</strong> <strong>the</strong> 1,694 cycles, respectively.Echogenic ovulatory follicles were observed atleast once during a breeding season in 16.0% <strong>of</strong> allmares. The age <strong>of</strong> mares exhibiting echogenicovulatory follicles (15.0 ± 5.4 years) was notsignificantly different (P>0.05) than age <strong>of</strong> maresnot exhibiting echogenic ovulatory follicles (11.8± 5.5 years). The mean interval from initialdetection <strong>of</strong> echogenic particles within <strong>the</strong>follicular fluid and ovulation was 1.4 ± 0.9 days.Ovulation was induced by hCG or GnRH in 87.3%<strong>of</strong> all oestrous cycles. Treatment with hCG orGnRH preceded detection <strong>of</strong> an echogenicovulatory follicle in 41.9% <strong>of</strong> cases.Administration <strong>of</strong> hCG or GnRH occurredfollowing detection <strong>of</strong> echogenic ovulatoryfollicles in 25.7% <strong>of</strong> cases and no hCG or GnRHwas administered before or after detection <strong>of</strong> anechogenic ovulatory follicle in 32.4% <strong>of</strong> cases.Embryo recovery data were recorded for 34mares that ovulated a single non-echogenic follicleor a single echogenic follicle during oestrouscycles within <strong>the</strong> same breeding season. Embryorecovery rate per flush was significantly higher(P