In vitro and in vivo embryo production in cattle superstimulated with FSH for 7 days
Mapletoft, R. JGuerra, A. GarcíaDias, F. C. FSingh, JAdams, G. P
Over the past two decades, research efforts have resulted in superstimulation protocols that are user-friendly, but embryo production has increased only marginally. Studies to-date have not adequately answered the question of whether superstimulatory protocols can be used to overcome the follicle wave pattern, increase the number of follicles that enter the wave, or rescue a greater number of small follicles within the wave. Studies which appear to facilitate greater utilization of follicles within the wave are described in this review. The number of large follicles at the time of first AI tended to be greater, and more ovulations and CL occurred with lengthened protocol (7-day) than with the convention 4-day FSH treatment. In addition, there was greater synchrony of ovulations and the mean numbers of total ova/embryos, fertilized ova, transferable or freezable embryos were numerically higher in the 7-day group. When used in an in vitro fertilization model, FSH treatment for 7 days resulted in a greater number of follicles for aspiration, a greater proportion of expanded cumulus-oocyte-complexes, and more transferable embryos after in vitro culture. Daily ultrasonography revealed a reduction in the number of small (1-2 mm) antral follicles from the beginning to the end of the superstimulatory treatment that was associated with a progressive shift of follicles to the next size category in both 4-day and 7-day groups. The number of follicles<5 mm decreased during superstimulation suggesting that there was no continuous recruitment of small follicles, and the number of follicles>1 mm at the end of superstimulation did not differ from the number of follicles >1 mm at the beginning of Super stimulation. However, the total number of follicles >3 mm at the end of superstimulation, was greater than the number of follicles >3 mm at the beginning of superstimulation due to growth of the 1-2 mm population into larger size categories during treatment. (AU)
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