Curry and Osteen (2001) reported that MMP-2 and MMP-9 were expressed in the developing follicles, where major diffusion of granulosa cells occurs. Chaffin and Stouffer (1999) also reported that the gelatinase activity of MMP-2 and MMP-9 was required for the modification of granulosa cells during follicle development. In this regard, the reduction in the ovulation rate in miniature pigs may be due to the low expression of MMP-9 in granulosa cells. Higher MMP-2 expression in the Graafian follicles of miniature pigs could not compensate for the lack of MMP-9, probably because MMPs are required before the LH level surge to ensure successful ovulation (Espey and Lipner 1994).