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

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Abstract
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 ≥ 10 small follicles 3–8 mm in diameter were classified as having no dominant follicle. In Expt 2 donors superovulated (once a day for 4 days) in the absence of a dominant follicle yielded more corpora lutea (15.5 ± 2.5 versus 4.5 ± 1.4, P < 0.01), ova and embryos (12.9 ± 2.8 versus 1.2 ± 0.4, P < 0.01) and transferable embryos (7.8 ± 2.5 versus 0.3 ± 0.2, P < 0.01) compared with donors treated in the presence of a dominant follicle. In Expt 3 donors superovulated (single s.c. injection) in the absence of a dominant follicle yielded more corpora lutea (11.2 ± 2.7 versus 1.9 ± 0.8, P < 0.01), ova and embryos (9.5 ± 2.7 versus 1.2 ± 0.6, P < 0.01) and transferable embryos (3.4 ± 1.3 versus 0.3 ± 0.2, P < 0.05) compared with donors treated in the presence of a dominant follicle. In Expt 4 donors were superovulated using one injection of FSH per day for 4 days and scanned four times at intervals of 2 days. In the absence of a dominant follicle donors yielded more corpora lutea (19.3 ± 2.3 versus 7.7 ± 1.6, P < 0.01), ova and embryos (17.4 ± 2.6 versus 5.1 ± 1.4, P < 0.01) and transferable embryos (10.3 ± 2.2 versus 1.0 ± 0.5, P < 0.01) than in the presence of a dominant follicle. In cows in which the dominant follicle had been aspirated under sonographical control 2 days before superovulation, the superovulatory response was similar to that in animals treated in the absence of a dominant follicle, and was significantly enhanced compared with animals superovulated in the presence of a dominant follicle (21.6 ± 2.2 corpora lutea, 18.7 ± 12.7 ova and embryos, 10.1 ± 1.5 transferable embryos). The major conclusions from this investigation are: (1) that the presence or absence of a dominant follicle can be detected by a minimized ultrasound scanning schedule using the number of small follicles as the major criterion; (2) the presence or absence of a dominant follicle significantly affects superovulatory responses in dairy cattle; and (3) ultrasound-guided follicular aspiration of the dominant follicle provides an accurate and reliable procedure to increase ovarian responses in dairy cattle possessing a dominant follicle.

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