Genetic correlations between gestation length and litter traits of sows
The aim of this study was to estimate genetic correlations between gestation length (GL) total number of piglets born (TB), number of piglets born alive (BA) and number of stillborn piglets (SB). Data of Landrace (LR), Large White (LW) and Duroc (DR) sows from one nucleus farm were analyzed. Data used in this study were 28,809 records of sows farrowing during 2006 to 2019. The factors effecting traits were examined by using GLM procedure in SAS program. Variance and covariance components were estimated using AIREMLF90 program. The model was applied with fixed effects for contemporary group, breed and parity, and random effects for animal, permanent environmental effect and residual effect. Heritabilities ranged from 0.26 to 0.32, 0.05 to 0.13, 0.07 to 0.12 and 0.01 to 0.03 for GL, TB, BA and SB, respectively. Genetic correlations between TB and BA were high (0.99) in all breeds. Genetic correlations of GL with TB and BA were negative. Genetic correlations between TB, BA and SB were positive. All the results suggest that selection for larger TB will increase BA and SB in LR and DR as well as decrease GL in DR. However, in LR and LW, selection for larger TB would probably result in a correlated decrease in GL. In regards to the positive genetic correlation between TB and SB, piglet mortality should be considered as a selection criterion to improve piglet survival. This study presents breed-specific estimates of genetic parameters for GL and litter traits in Thailand. It provides information to apply in breeding program for specific breed.