Supplementation of semen extender with caffeine and CaCl(2) for artificial insemination (AI) of fresh spermatozoa has been demonstrated to reduce recruitment of uterine polymorphonuclear leukocytes (PMNs) and the activity of phagocytosis. Here, we determined if addition of caffeine and CaCl(2) to semen extender improves the fertility of frozen-thawed boar semen. In experiment 1, gilts were cervically inseminated twice with frozen-thawed boar spermatozoa (25 x 10(8) cells per dose) suspended in Modena solution (n=7) or modified Beltsville Thawing Solution supplemented with caffeine and CaCl(2) (BCC, n=7). The gilts were slaughtered 4 h later, and their oviducts and uterine horns plus the body of the uterus were flushed to recover PMNs and non-phagocytosed spermatozoa. There was no difference in the total number of uterine PMNs between gilts inseminated with Modena solution and those inseminated with BCC (3.8 x 10(8) vs. 1.5 x 10(8) cells, respectively); however, the total number of uterine spermatozoa was higher when gilts were inseminated with BCC (40.6 x 10(6) cells) compared with those inseminated with Modena solution (1.4 x 10(6) cells, P<0.05). In experiment 2, gilts and sows were subjected to intrauterine insemination twice with frozen-thawed spermatozoa suspended (25 x 10(8) sperm per dose) in Modena (n=21) or BCC (n=21). The overall pregnancy and farrowing rates were higher in females inseminated with BCC (71.4 and 61.9%, respectively) compared with those inseminated with Modena solution (38.1 and 28.6%, respectively, P<0.05). However, no significant difference in litter size of piglets was observed between treatments (7.2 +/- 1.6 piglets for Modena solution vs. 8.2 +/- 0.9 piglets for BCC solution). In conclusion, we demonstrated that use of BCC solution for frozen-thawed boar semen produced better pregnancy and farrowing rates following AI than Modena solution, probably by reducing the phagocytosis of spermatozoa.