229. Effect of follicular status on sheep embryo yields is mediated by changes in the preovulatory LH surge

Abstract

Follicular status at the start of superovulatory treatment (presence/absence of a dominant follicle/corpus luteum) has been reported to affect subsequent embryo yields.¹ The aim of the current study was to assess if this effect may be exerted through changes in the occurrence, or characteristics, of the preovulatory LH surge. Forty-three Manchega ewes were superovulated with eight decreasing doses of oFSH (OVAGEN^TM), starting on Day 12 after the insertion of a progestagen intravaginal sponge. At the first two FSH doses, diameter of both largest follicles (LF1 and LF2, respectively) were determined by ultrasonography. Blood sampling for LH determination was performed from 18 to 60 h after progestagen withdrawal. Ewes were also mated between 18 and 60 h after sponge withdrawal and embryos were recovered and evaluated on Day 21, being in vitro cultured until hatching. Moreover, the effect of the LH surge on superovulatory yields showed that ewes showing LH surges either with later onset or shorter duration showed higher rates of embryo viability after in vitro culture (r = 0.461, P < 0.005 and r = 0.980, P < 0.0005). In addition, earlier LH surges were related to a decreased number of non-viable embryos at recovery (r = 0.777, P < 0.05), due to a higher number of degenerated embryos, and to a lower viability rate after in vitro culture (r = 0.521, P < 0.05 and r = 0.562, P < 0.0005). Finally, the current study showed that ewes with a higher difference between LF1 and LF2 displayed earlier LH surges (r = 0.420, P < 0.05), which is related to decreased embryo yields (r = 0.777, P < 0.05).

   (1) Gonzalez-Bulnes et al. (2002). Theriogenology 58, 1607–1614.