Effect of number of motile, frozen-thawed boar sperm and number of fixed-time inseminations on fertility in estrous-synchronized gilts

There are advantages for use of frozen-thawed boar sperm (FTS) as a tool for preservation and transfer of valuable genetic material, despite its practical limitations. It was hypothesized that increasing the number of motile FTS and number of fixed-time artificial inseminations (AI) would improve pregnancy rate and litter size. Semen from six boars was frozen in 0.5 mL straws at 500 x 10(6) cells/mL Gilts similar to 170 days of age, were induced into estrus with PG600 (R) and synchronized using MATRIX (TM) (synthetic progestagen). Following last feeding of MATRIX (LFM), gilts were checked twice daily for estrus. At onset of estrus, gilts were randomly assigned in a 3 x 2 factorial treatment design to receive 1 x 10(9) motile FTS (n = 19), 2 x 10(9) motile FTS (n = 19), 4 x 10(9) motile FTS (n = 19) in a single AI at 32 h after onset of estrus, or 1 x 10(9) motile FTS (n = 18), 2 x 10(9) motile FTS (n = 17), or 4 x 10(9) motile FTS (n = 19) in each of the two AI at 24 and 32 h following onset of estrus. Ultrasonography was performed at 12 h intervals after estrus to estimate time of ovulation. Reproductive tracts were collected 28-34 days following AI. Estrus occurred at 139 2 h (mean SE) after LFM and ovulation at 33 +/- 1 h following onset of estrus. Dose and number of inseminations did not interact or individually influence pregnancy rate at slaughter (73 +/- 4.2%) or numbers of normal fetuses (10.8 +/- 0.5). However, number of fetuses tended (P = 0.14) to increase with double AI but not with dose. Boar did not affect pregnancy rate but did affect number of normal fetuses and embryonic survival (P < 0.01). Longer intervals from insemination to ovulation reduced pregnancy rate (P < 0.05), number of normal fetuses (P < 0.001). and embryonic survival (P < 0.01). Ovarian abnormalities at slaughter were associated with reduced pregnancy rate (P < 0.001). The results of this experiment indicate that a double insemination using 2 x 10(9) motile sperm would produce the greatest number of piglets with fewest numbers of frozen sperm used, while double AI with 1 x 10(9) motile sperm would be most practical for pig production with limited genetic resources. Fertility was also influenced by boar, interval from insemination to ovulation, and gilt ovarian abnormalities. (C) 2010 Elsevier B.V. All rights reserved.