Submitted to: Animal Reproduction Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/5/2010
Publication Date: 7/13/2010
Citation: Spencer, K.W., Purdy, P.H., Blackburn, H.D., Spiller, S.F., Stewart, T.S., Knox, R.V. 2010. Effect of number of motile frozen-thawed boar sperm and number of fixed-time inseminations on fertility in estrous-synchronized gilts. Animal Reproduction Sciences. 121:259-266. Interpretive Summary: Frozen-thawed boar sperm (FTS) can be used as a tool for preservation and transfer of valuable genetic material. The problem with using it is that the resulting fertility and litter size is reduced due to the injurious effects of freezing the sperm. We hypothesized that the number of motile FTS and number of timed artificial inseminations (AI) would influence the pregnancy rate and litter size. We determined that 1.0, 2.0, or 4.0 billion motile FTS in a single AI or a double AI did not affect the fertility or litter size. We also determined that the interval from estrus to ovulation did affect the pregnancy rate, number of normal fetuses, and embryo survival. These results are important to the swine industry because they demonstrate that proper management of gilts can result in acceptable fertility but only if the estrus and time of ovulation is monitored. These results are also important because they demonstrate that a low dose insemination (1.0 billion motile sperm), and two AIs, can be used to achieve acceptable fertility which will be cost saving methods compared to the 4 to 6 billions sperm and 3 AIs typically used in the swine industry.
Technical Abstract: 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. We hypothesized that increasing the number of motile FTS and number of timed artificial inseminations (AI) would improve pregnancy rate and litter size. Semen from 6 boars was frozen in 0.5 mL straws at 500 million cells/mL. Gilts (~170 d of age) were induced into estrus with PG600 and synchronized using Matrix. Following last feeding of Matrix (LFM), gilts were checked twice daily for estrus and then assigned to receive 1.0, 2.0, or 4.0 billion motile, FTS in a single AI at 32 h, or a double AI at 24 and 32 h after detection of estrus. Ultrasound was performed at 12 h intervals after estrus to determine time of ovulation. Reproductive tracts were collected on d 32 following AI. For all gilts, estrus occurred at 139 ± 2 h (mean ' SE) after LFM and ovulation occurred at 33 ± 1 h following onset of estrus. Dose and number of inseminations did not affect pregnancy rate at d 25, or at slaughter (range: 66-87%), or numbers of normal fetuses (range: 9.5-12.6). Number of inseminations did not influence pregnancy rate but double AI did tend (P=0.14) to increase number of normal fetuses. Boar did not affect pregnancy rate but did affect number of normal fetuses and embryo survival (P<0.01). Interval from estrus to ovulation tended to affect pregnancy rate at d 25 (P=0.12), and at slaughter (P<0.05), number of normal fetuses (P<0.001), and embryo survival (P<0.01). Ovarian abnormalities at slaughter influenced pregnancy rate at d 25 and at slaughter (P<0.001) and tended to affect numbers of normal fetuses (P=0.11). The results of this experiment indicate that low numbers of sperm and single inseminations can result in acceptable pregnancy rates and litter sizes, but fertility improvements tend to occur with higher numbers of sperm and double inseminations. Fertility outcomes when using frozen boar semen are influenced by boar, interval from estrus to ovulation, and gilt ovarian status. Future methodology should focus on lowering sperm numbers, improved AI timing, and selection for boar and gilt fertility.