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 di ameter in a growing phase; stable for < 3 days) for the superovulatory response in 117 lactating Holstein Friesian dairy cows was investigat ed. The presence or absence of a dominant follicle was determined retr ospectively by analysing videotapes of follicular growth in all the ov aries. Superovulation was induced by 28 mg Armour units (400 mg NIH-FS H-P1) of FSH (Folltropin(TM)) 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 supe rovulation 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 an d 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 donor s treated in the presence of a dominant follicle. In Expts 2 and 3 don ors were scanned only on the day of superovulation and donors with < 1 0 follicles 3-8 mm in diameter were considered to have a dominant foll icle, while donors with greater than or equal to 10 small follicles 3- 8 mm in diameter were classified as having no dominant follicle. In Ex pt 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 fol licle. In Expt 3 donors superovulated (single s.c. injection) in the a bsence 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 d ominant follicle. In Expt 4 donors were superovulated using one inject ion 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 corpo ra 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 d ominant follicle. In cows in which the dominant follicle had been aspi rated under sonographical control 2 days before superovulation, the su perovulatory response was similar to that in animals treated in the ab sence 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 t ransferable embryos). The major conclusions from this investigation ar e: (1) that the presence or absence of a dominant follicle can be dete cted by a minimized ultrasound scanning schedule using the number of s mall 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 d ominant follicle provides an accurate and reliable procedure to increa se ovarian responses in dairy cattle possessing a dominant follicle.