Assessment of the presence of a dominant follicle and selection of dairy cows suitable for superovulation by a single ultrasound examination.

The physiological significance of the dominant follicle (> 9 mm in diameter in a growing phase; stable for < 3 days) for the superovulatory response in 117 lactating Holstein Friesian dairy cows was investigated. The presence or absence of a dominant follicle was determined retrospectively by analysing videotapes of follicular growth in all the ovaries. Superovulation was induced by 28 mg Armour units (400 mg NIH-FSH-P1) of FSH (Folltropin) administered either twice or once a day i.m. over 4 days in a decreasing regimen or as a single injection s.c. Donors were scanned daily from day 3 after the oestrus preceding superovulation until embryo recovery. In Expt 1 donors superovulated (two times a day for 4 days) in the absence of a dominant follicle yielded more corpora lutea (11.7 +/- 0.9 versus 4.7 +/- 1.1, P < 0.01), ova and embryos (8.2 +/- 1.2 versus 2.8 +/- 1.0, P < 0.01) and transferable embryos (5.0 +/- 1.0 versus 2.1 +/- 0.9, P < 0.05) compared with donors treated in the presence of a dominant follicle. In Expts 2 and 3 donors were scanned only on the day of superovulation and donors with < 10 follicles 3-8 mm in diameter were considered to have a dominant follicle, while donors with > or = 10 small follicles 3-8 mm in diameter were classified as having no dominant follicle.(ABSTRACT TRUNCATED AT 250 WORDS)