Effects of back fat, growth rate, and age at first mating on Yorkshire and Landrace sow longevity in China

In the present study, genetic parameters for longevity and genetic correlations with back fat (BF), average daily gain (ADG), and first mating age (FMA) were estimated from 19 300 Yorkshire and 18 378 Landrace sows from 12 farms derived from one breeding system. General linear models (GLM) were employed to estimate genetic correlations with heritability (h2). Longevity was defined by six different parameters (i.e., traits) and heritability ranged from h2=0.13 to 0.16 (P<0.05) in both swine breeds. Genetic correlations between different longevity definitions were positive and high (r=0.79 to 0.99; P<0.05). BF exhibited low positive genetic correlations (r=0.12 to 0.15; P<0.05) with longevity traits identified in both pig breeds which were dependent on trait definition, whereas ADG and FMA showed weak negative genetic correlations with longevity traits. The influence of BF, ADG, and FMA on longevity traits was examined by dividing the production and reproductive traits into several numerical groups; the influence of each longevity trait was subsequently analyzed among the different groups. The results indicated BF was the best trait to improve longevity among BF, ADG, and FMA, which showed positive effects for almost all longevity traits. For Yorkshire sows, gilts with over 18 mm BF were most desirable; Landrace with 10.6-13 mm BF were suitable for longevity. ADG was not favorable for gilt selection, because the correlation between growth rate and longevity very low. For FMA, our results indicated gilts mating before 230 days exhibited a longer life span. Therefore, we suggest farmers should select for thicker back fat and mate at an earlier age to improve sow longevity.