Follicular dynamics and gene expression in granulosa cells, corpora lutea and oocytes from gilts of breeds with low and high ovulation rates P. V. Silva A , S. E. F. Guimara˜es A,E , J. D. Guimara˜es B , C. S. Nascimento A , P. S. Lopes A , J. B. Siqueira A , L. S. Amorim B , F. Fonseca e Silva C and G. R. Foxcroft D A Departamento de Zootecnia, Universidade Federal de Vicosa, Vicosa 36570-000, MG, Brasil. B Departamento de Veterina´ria, Universidade Federal de Vicosa, Vicosa 36570-000, MG, Brasil. C Departamento de Estatı ´stica, Universidade Federal de Vicosa, Vicosa 36570-000, MG, Brasil. D Swine Reproduction-Development Program, Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton T6G 2P5, AB, Canada. E Corresponding author. Email: sfacioni@ufv.br Abstract. Follicular dynamics and the expression of candidate genes using real-time polymerase chain reaction (PCR) were compared during the oestrous cycle of pig breeds with high (commercial line; n ¼ 24) and low (local Brazilian Piau; n ¼ 21) ovulation rates and prolificacy. Gilts were killed on Days 0, 4, 10 and 18 of the oestrous cycle and visible ovarian follicles were classified by follicular diameter. Recovered cumulus–oocyte complexes were classified as normal or atretic and frozen in liquid nitrogen until RNA extraction. Low ovulation rates and/or prolificacy in Piau gilts was associated with a different pattern of follicle development, with lower numbers of small follicles on Day 18, fewer large follicles on Days 0 and 18 (P # 0.05) and a higher proportion of atretic follicles on Days 0 and 18 (P # 0.05). Compared with commercial line gilts, less-prolific Piau gilts exhibited higher expression of apoptotic genes during luteolysis (CASP3 and FASL; P # 0.05), decreased expression of TGFBR2 and BAX mRNA in the corpus luteum (P # 0.05), higher expression of apoptotic genes (FAS, BCL2 and CASP8; P # 0.05) in granulosa cells and a greater abundance (P # 0.05) of genes controlling oocyte- secreted factors (GDF9, BMP15 and BMP6), suggesting underlying mechanisms controlling differences in follicular development, ovulation rate and inherent prolificacy in this pig breed. Additional keywords: growth factors, litter size, ovulation. Received 7 August 2012, accepted 12 January 2013, published online 7 March 2013 Introduction As in sheep, differences in ovulation rate in different breeds of pigs are presumably linked to differences in intraovarian regu- latory mechanisms and overall prolificacy. For example, according to Manabe et al. (2004), the higher ovulation rate in the Meishan sow is related to differences in both follicular recruitment and atresia. The same group reported that a lower ovulation rate and a smaller number of pigs born in local Hun- garian Mangalica sows compared with other European breeds was also related to differences in follicle recruitment and atresia (Ra´tky et al. 2005). It has been postulated that follicles of Meishan sows provide a ‘better’ environment for oocyte matu- ration than follicles of Large-White hybrid sows, which may also contribute to the prolificacy of Meishan sows (Bazer et al. 1988a; Haley and Lee 1993; Hunter and Picton 1995). Similarly, different patterns of follicle and oocyte development may exist between prolific commercial breeds and the less prolific Brazilian Piau breed, and comparative studies using these breeds may contribute to the identification of genes related to ovulation rate, oocyte quality and consequently embryonic development and survival in the pig. Preliminary studies comparing different traits in contemporary commercial sows with sows from the less-prolific Brazilian Piau breed (Silva et al. 2011) have revealed differences in ovulation rate (15.5  1.9 vs 11.1  2.4, respectively; P # 0.05), the number of total pigs born (TB; 14.3  3.7 vs 9.3  2.7, respectively; P # 0.05) and pigs born alive (BA; 12.7  3.1, 7.9  2.6, respectively; P # 0.05). Because the Piau breed has never been subjected to intensive genetic selection, it may carry allelic variants that are no longer found in highly selected and more prolific commercial lines. The growth and development of ovarian follicles requires a series of coordinated events that lead to follicular somatic cell differentiation, oocyte maturation and ovulation (Bonnet et al. 2008). In farm species, the number of ovulatory follicles is CSIRO PUBLISHING Reproduction, Fertility and Development, 2014, 26, 316–327 http://dx.doi.org/10.1071/RD12257 Journal compilation Ó CSIRO 2014 www.publish.csiro.au/journals/rfd