Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2012
Publication Date: 8/1/2012
Citation: Freking, B.A., Purdy, P.H., Spiller, S.F., Welsh, C.S., Blackburn, H.D. 2012. Boar sperm quality in lines of pigs selected for either ovulation rate or uterine capacity. Journal of Animal Science. 90(8):2515-2523.
Interpretive Summary: Improvement in boar fertility can result from increased numbers of sperm produced and/or improving their ability to fertilize eggs. As the swine industry has evolved into greater use of artificial insemination, a better understanding of the genetic basis for the tremendous amount of variation among boars and between lines of boars would be of economic value to swine producers and boar studs. Industry selection among and within lines for reproduction has focused more on female reproductive traits. It is not entirely clear what the correlated impact on male reproduction has been within maternal lines. If the relationship is negative in response to improved female reproduction this would generate a negative economic impact on the components of the industry producing replacement females. Selection for 11 generations in swine for ovulation rate (OR) or uterine capacity (UC) resulted in significant changes in component traits of litter size. Our objective was to conserve the unique germplasm for the future and to characterize male sperm quality as a correlated response to the selection criterion imposed compared to an unselected control line (CO). Boars representing genetic diversity available in all 3 lines were produced in 2 replicate farrowing seasons. In the current pig experiment, the OR line was observed to have a small but favorable response in total sperm production while in the UC line levels were intermediate to those for OR and CO. Thus, direct selection of females for independent component traits of litter size represented by OR and UC lines resulted in small but positive changes in male sperm production. While line differences were detected in the current experiment for some sperm quality measures, the differences were not large and not consistent across processing time points. Differences between individual boars were larger than what was observed for average line differences. Information obtained in this study would indicate that the selection criterion for increased ovulation rate or uterine capacity imposed on females has resulted in modest increased sperm production in males with minor changes to sperm quality or movement parameters.
Technical Abstract: Selection for 11 generations in swine for ovulation rate (OR) or uterine capacity (UC) resulted in significant changes in component traits of litter size. Our objective was to conserve the unique germplasm for the future and to characterize sperm quality as a correlated response to the selection criterion imposed compared to an unselected control line (CO). Boars representing genetic diversity available in all 3 lines were produced in 2 replicate farrowing seasons. Replicate 1 was born in September 2005 and sampled for semen characteristics in October 2006. Replicate 2 was born in March 2006 and sampled for semen characteristics in February and March 2007. Each boar (n = 60) was collected twice. The sperm-rich fraction was obtained and volume and concentration of sperm cells were measured to estimate total sperm production. Each ejaculate was extended 1:3 vol/vol with Androhep Plus (Minitube, Verona, WI) and packed for shipping to the NAGP lab for processing into frozen straws. Semen quality was measured by computer assisted semen analysis at 3 semen processing points: fresh (F), 24 h after extender added (E), and post-thaw (PT). A mixed model analysis of variance was applied to the data. Fixed effects of farrowing season, line and two-way interactions were fitted. Random effect of boar (n = 60) within farrowing season and line was used to test line differences. Sperm concentration was not different (P = 0.18) among the lines (0.594 x 10**9, 0.691 x 10**9, and 0.676 x 10**9 cells/ml) for CO, OR, UC lines, respectively. However, significance (P = 0.04) was detected for volume of the sperm-rich fraction, greatest for OR (86.4 ml), intermediate for UC (75.5 ml), and lowest for CO (70.2 ml). Line differences were thus detected (P = 0.02) for total sperm production per ejaculate, greatest for OR (54.9 x 10**9), intermediate for UC (48.7 x 10**9) and lowest for CO (40.5 x 10**9). A higher percentage of progressively motile sperm and higher estimates of sperm velocity only at processing point E (P < 0.01) were detected in favor of CO. Estimates of motility, velocity, and other parameters of sperm movement measured on E processing points were positively correlated with estimates obtained PT but the magnitude was low to moderate (r range -0.04 to 0.27). Thus, selection for component traits of female reproduction had a favorable effect on total sperm production of boars.