Winemaking by-products and grape polyphenol extracts as phytogenic additives for rations in pig production. Review

Winemaking by-products, such as grape pomace, seed and skin, represent a rich source of phenolic compounds (PC), fiber, fatty acids and essential nutrients, which has received great interest in pig production systems. Regarding their profile and PC content, previous studies have shown that these by-products can exert multiple bioactive properties on animal health, nutrition and production, even beneficial effects have been observed in pigs. Furthermore, these by-products and wine polyphenol extracts have been considered valuable ingredients and a promising alternative to replace conventional resources in monogastric diets and thus reduce feed costs. However, these by-products are discarded and disposed of inappropriately. In fact, only 3% of recovered by-products are used in animal nutrition without prior treatment. Therefore, emphasis has been placed on generating added value to winemaking by-products to obtain more significant economic and technological benefits and greater efficiency in animal production. This review discusses the most relevant and recent studies on the inclusion of winemaking by-products and their CF during each stage of the pig production system (gestation-lactation, weaning, growth and finishing) and their effects on the final quality of meat and its derivatives. In addition, strategies and treatments applied for the use of pomace in pig diets are described.