Effects of an herbal diet, diet x boar line and diet x genotype interactions on skin lesions and on growth performance in post-weaning pigs using a cross-classified experiment

Abstract

The aims of the present study were to assess the effect of an herbal diet (HD; basal diet plus a supplement with chicory herbs) on production traits and lesions scores in post weaning pigs, and to study possible boar x diet and genotype x diet interactions considering the two feeding groups HD and control (CON). In this regard, a cross-classified research design was implemented, aiming on an equal number of boar offspring in both groups HD and CON. Grouping of piglets (993 crossbred piglets from 14 different Piétrain boars sire to German Landrace or German Edelschwein sows) was done after weaning, and the feeding experiment was conducted in post-weaning period up to the pig age of nine weeks. Studied traits included the post-weaning weight (PWW) at the age of nine week 9, average daily gain (ADG) considering the period from weaning until week 9 and a skin lesion score (LS) at week 9. Herbal diet effects and sire x diet effects were inferred via linear models for Gaussian distributed PWW and ADG, and via generalized linear mixed models with a logit link function for categorical LS. Possible genotype x diet interactions were proved in multiple-trait models via Gibbs sampling, by defining same traits recorded either in CON and HD as different traits, i.e., post-weaning weight control (PWWCON) and post-weaning weight herbal diet (PWWHD), average daily gain control (ADGCON) and average daily gain herbal diet (ADGHD), and lesion score control (LSCON) and lesion score herbal diet (LSHD). The dietary treatment had no significant effect (P > 0.05) on PWW and ADG. The dietary treatment significantly (P < 0.05) influenced the behavior of the pigs, with a lower and favorable LS score for the pigs allocated to HD. Significant sire x diet interactions were identified for LS, PWW and ADG. Pearson correlations between estimates for sire effects from both diets CON and HD (i.e., the sire x diet effect) were 0.84 for PWW, 0.71 for ADG and 0.56 for LS. Genetic correlations smaller than 0.80 between PWWCON and PWWHD, ADGCON and ADGHD, and LSCON and LSHD indicate genotype x diet interactions, especially for the functional and low heritability LS. Hence, re-rankings of sires according to their estimated breeding values (EBV) were observed in both environments CON and LD, displaying smaller genetic and EBV variations for LS in the HD group. The HD dietary supplement contributed to fewer skin lesions, probably due to the favorable effect on pig behavior, but a more pronounced genetic differentiation seems to be possible in the more challenging CON environment. Generally, the results from the present study indicate the importance of genotype x feeding interactions for pig breeding, suggesting specific boars for different feeding environments.