Variance component estimates for alternative litter size traits in swine

Area of Science:

• Animal Breeding and Genetics
• Swine Production

Background:

• Litter size at day 5 (LS5) is established for improving total number born (TNB) and reducing preweaning mortality.
• Optimal timing for selection based on litter size traits is crucial for maximizing genetic gains in swine breeding programs.

Purpose of the Study:

• To identify the optimal day for litter size selection beyond day 5.
• To evaluate various litter size traits and their genetic parameters over time.
• To assess the potential of litter size at day 10 (LS10) as a maternal selection trait.

Main Methods:

• Utilized bivariate animal models incorporating fixed effects (farm, season, parity) and random effects (additive genetics, permanent environment).
• Analyzed traits including total number born (TNB), number born alive (NBA), litter size at various days (LS2-LS30), litter size at weaning (LSW), number weaned (NW), piglet mortality (MortD30), and birth weight (BirthWt).
• Estimated variance components and genetic correlations to assess trait changes and relationships over lactation.

Main Results:

• Additive genetic variance for litter size was minimized around day 7 (Large White) and day 14 (Landrace).
• Heritability estimates for litter size traits ranged from 0.07 to 0.13, increasing towards weaning.
• High genetic correlations (0.97-1.00) were found between LS10 and number weaned (NW), suggesting LS10's utility as a maternal trait.

Conclusions:

• Litter size at day 10 (LS10) presents a viable compromise for selection, balancing weaning performance with reduced negative influences.
• LS10 can be effectively used as a maternal trait, particularly when cross-fostering is minimal.
• Selection based on LS10 can contribute to improved swine production efficiency by enhancing both litter size and survival rates.