A major unsolved welfare issue in pigs is aggressive and tail biting behaviour. This behaviour is induced by environmental, genetic, and nutritional factors. Genetic components as well as genotype by environment interactions have been identified to affect primary and functional trait responses to biting in pigs. Furthermore, one key trigger for tail biting is the length of the tail. The persistence of tail biting in commercial farm conditions has resulted in the majority of large pig enterprises considering docking of the tails of all piglets as a preventative measure, which does not correspond with legal animal welfare guidelines. Nevertheless, the future is to keep pigs with naturally long tails, implying improvements in animal breeding and behaviour. It remains unclear why some pigs are not victims of this aggressive behaviour in farm houses. Furthermore, it is imperative to identify the exact causes of abnormal behaviour, especially from a genetics perspective. Aggressive behaviour and tail biting in pigs can be mitigated by the use of breeding strategies and the modification of the production environment. This study focuses on the traits tail length, skin lesions and active behaviour pattern of pigs in the context of genetics, feeding and genotype by feeding interactions in pigs. Due to the lack of investigations in the literature addressing genetic parameters for tail characteristics and its effect on growth traits, Chapter 2 is the first comprehensive report on genetic parameters for tail length (T-LEN). The chapter reported on T-LEN and growth traits: birth weight (BW), weaning weight (WW), post-weaning weight (PWW), and average daily gain (ADG) from 9,348 piglets from the University of Gießen research station. In addition, 4,943 binary observations from 1,648 pigs for tail lesions (T-LES) as indicators for tail necrosis, tail abnormalities, or tail biting were included in this analysis. T-LES were recorded at 30 ± 7 days after entry for rearing (T-Les-1), at 50 ± 7 days after entry for rearing (end of the rearing period, T-LES-2), and 130 ± 20 days after entry for rearing (end of fattening period, T-LES-3). Heritability estimate for T-LEN was 0.42 (± 0.03), indicating the potential for genetic selection on short tails. The maternal genetic heritability for T-LEN (0.05 ± 0.04), indicating the influence of uterine characteristics on morphological traits. The negative correlation between direct and maternal effects for T-LEN of – 0.35 (± 0.13), as well as the antagonistic relationships between T-LEN with the growth traits BW, WW, PWW, and ADG, complicate selection strategies and breeding goal definitions. The heritability for T-LES when considering the three repeated measurements was 0.23 (± 0.04) from the linear (repeatability of 0.30) and 0.21 (± 0.06; repeatability of 0.29) from the threshold model. The breeding value correlations between T-LES-3 and breeding values from the repeatability models were quite large (0.74 to 0.90), suggesting tail lesion recording at the end of the rearing period. Nutrition plays a major role in pig behaviour such as the favourable feeding effects of the chicory herbal diet to reduce aggressiveness and simultaneously improve growth performance. For this reason, the aim of Chapter 3 was to assess the feeding effect of the chicory herbal diet on production traits and lesions scores, and to study possible boar-diet and genotype by diet interactions in post weaning pigs. A cross-classified research design was implemented, focussing on an equal number of boar offspring in both feeding groups. Findings in chapter 3 indicate that the dietary treatment had no significant effect (P 0.05) on growth traits (PWW and ADG). However, the dietary treatment significantly (P weiterlesen