## 4 Discussion  
The results of the present study showed that the examined levels of chestnut wood extract or hop cones supplementation exerted no effect on carcass traits. When a similar extract rich in hydrolysate tannins was used, a dose-dependent influence on productive traits was demonstrated, i.e., no differences when small amounts (up to 2%) of sweet chestnut wood extract were added [33; 34; 35], whereas an addition of 3% resulted in reduced feed intake, which was attributed to reduced palatability of the diet [36; 37]. Supplementing the pigs' diet with a chestnut meal also showed improved performance (feed efficiency) at a lower level of inclusion (30 vs. 50 or 100 g/kg dry matter) [38]. As considered for the supplementation with hops, no effect of feeding diets added with hops water extract on the performance of growing pigs was observed [39]. Regarding the supplementation with hops, no studies were performed in fattening pigs, however, a positive effect of hops supplementation was reported for growing pigs [40; 41]. The studies in other species reported positive effects in chickens [42; 43], no major effect in fattening steers [44] and heifers [45], and even a negative effect on the growth rate in lambs [18]. There was also no major effect observed on WHC. Contrary to our study, a lower WHC (higher thawing [9] and total [37] loss) was observed in the entire male pigs supplemented with 3% of sweet chestnut wood extract and in Cinta Senese pigs fed solely chestnut for 3 months [46]. On the other hand, other studies reported no effect of sweet chestnut extract on cooking loss [19; 47] in agreement with the results of the present study. Considering hops supplementation, an improved WHC was reported by [PERSON] and [PERSON] [16], while [PERSON] et al. [17] observed no differences in the WHC of pigs supplemented with hops \(\beta\)-acids. In our study, no effect of hops supplementation on WHC was observed in fresh meat, however, a tendency for a lower salting phase loss in hams was observed. Processing losses in the salting phase are negatively correlated with carcass fatness due to the effect of fat as a barrier for water migration [48]. In our study, no significant differences were observed in fat depots (subcutaneous fat or IMF) in agreement with other studies where sweet chestnut wood extract [19; 33] or hops [18] were included in the animals' diet. A lower WHC can also be associated with higher oxidation rates [49], which lead to denaturation of proteins thus hindering the ability to bind water [50]. However, we observed no differences in oxidation of meat and backfat detected either by means of carbonyl groups or Rancimat, respectively. Contrary to our results, significant effects of feeding tannins and hops on oxidation parameters were found in other studies. A pro-oxidant effect (higher MDA and carbonyl groups concentration) in fresh LT muscle of pigs supplemented with 3% of sweet chestnut wood extract, along with a higher thawing loss, was reported by [PERSON] et al. [19]. The same study reported a lower oxidation (MDA concentration) in pigs supplemented with 2 and 3% of the extract in cooked meat samples. No effect on MDA concentration of fresh and cooked breast muscle was observed in sweet chestnut wood extract supplemented broiler chickens [7; 51]. In rabbits, a lower iron-induced lipid oxidation was reported when the animals were fed diets containing 0.5% of chestnut tannins, while a pro-oxidant effect was observed at 1% of inclusion [8]. Considering supplementation with hops, only a few studies reported its influence on the oxidative stability of meat. A higher oxidative stability of LT muscle after six months of storage at \(-20\)\({}^{\circ}\)C was reported in pigs supplemented with hops water extract [16; 39]. A lower oxidation of proteins in broiler chickens dietary supplemented with hop \(\beta\)-acids was reported by [PERSON] et al. [52], while no differences in muscle or liver TBARS were observed in hop supplemented rabbits [18].