Estimates of Genetic Correlations between Production and Semen Traits in Boar

Abstract

Currently, boars selected for commercial use as AI sires are evaluated on grow-finish performance and carcass characteristics. If AI sires were also evaluated and selected on semen production, it may be possible to reduce the number of boars required to service sows, thereby improving the productivity and profitability of the boar stud. The objective of this study was to estimate genetic correlations between production and semen traits in the boar: average daily gain (ADG), backfat thickness (BF) and muscle depth (MD) as production traits, and total sperm cells (TSC), total concentration (TC), volume collected (SV), number of extended doses (ND), and acceptance rate of ejaculates (AR) as semen traits. Semen collection records and performance data for 843 boars and two generations of pedigree data were provided by Smithfield Premium Genetics. Backfat thickness and MD were measured by real-time ultrasound. Genetic parameters were estimated from five four-trait and one five-trait animal models using MTDFREML. Average heritability estimates were 0.39 for ADG, 0.32 for BF, 0.15 for MD, and repeatability estimates were 0.38 for SV, 0.37 for TSC, 0.09 for TC, 0.39 for ND, and 0.16 for AR. Semen traits showed a strong negative genetic correlation with MD and positive genetic correlation with BF. Genetic correlations between semen traits and ADG were low. Therefore, current AI boar selection practices may be having a detrimental effect on semen production.

Genetic correlations between production and semen traits in pig

“…The advantage of using average values is a simplification of the numerical procedures. According to Oh et al (2006), the heritabilities calculated for the average values of semen traits are identical to the repeatabilities for semen traits defined per collection, since permanent environmental effects were not separated in the model when using average values. Probably it would be more proper to replace 'identical' by 'similar'.…”

“…Therefore it is difficult to draw unambiguous conclusions from these results. Oh et al (2006) found that genetic correlations between average daily gain and semen traits were generally low and not different from zero and that genetic correlations between backfat thickness and semen traits (semen volume, sperm concentration, total number of spermatozoa and number of extended doses) were positive in sign; therefore, selection against backfat thickness (for high lean meat content) would have a negative effect on semen traits. The latter authors admit that the estimates of genetic correlations may be biased due to the inability to properly account for the boar's permanent environmental effect.…”

“…Genetic correlations between production and semen traits estimated by Grandjot et al (1997) and Oh et al (2006) are summarized in Table 7. Grandjot et al (1997) estimated the genetic correlations between production and semen traits on two datasets with 192 and 174 observations (boars).…”

“…Genetic correlations between production and semen traits were estimated by Grandjot et al (1997) and Oh et al (2006). Average values of semen traits were used in both of these papers whereas measurements from individual ejaculates were used in our investigation.…”

“…To answer this question, knowledge on the genetic correlations between production and semen traits is necessary. Estimates of genetic correlations were published by Grandjot et al (1997) and Oh et al (2006). In both the cited papers, correlations were estimated from average values for semen traits.…”