Vegetable By-Products as Alternative and Sustainable Raw Materials for Ruminant Feeding: Nutritive Evaluation and Their Inclusion in a Novel Ration for Calf Fattening

SIMPLE SUMMARY: Large amounts of vegetable by-products are generated by the agri-food industry every day. Giving them a second life can be positive for the producing companies, with a special emphasis on improving their sustainability indicators. In addition, vegetable by-products are promising raw materials for ruminant nutrition. In this study, first, we evaluated the nutritional composition, in vitro digestibility, and gas production kinetics of 15 vegetable by-products using corn silage as the positive control. From these results, the second part of the research was focused on the formulation of two different diets for fattening calves: a conventional ration based on concentrate and straw and an alternative one based on vegetable by-products. Most vegetable by-products revealed greater nutritive value than corn silage and results indicated that their inclusion in finishing cattle diets may reduce the use of other ingredients without impairing ruminal fermentation. ABSTRACT: This research aimed to evaluate the nutritional composition, in vitro digestibility, and gas production kinetics of 15 vegetable by-products generated by the agri-food industry compared with corn silage as a reference raw material. Nutritional characterization and in vitro ruminal fermentation tests were performed to determine in vitro organic matter digestibility and digestible energy values, short-chain fatty acids, and the gas production profile. Results indicate that vegetable by-products were more degradable, more extensively fermented, and fermented at a faster rate than corn silage. Going one step further in the valorization of these by-products in animal feed, the second part of the research aimed to compare the novel ration designed for calf fattening with a conventional one. An artificial rumen unit was used to obtain nutrient disappearance, rumen fermentation parameters, and gas production of rumen digesta. Very slight differences were observed between both experimental rations, with their composition being the main difference. Most of the unitary vegetable by-products and all mixes, as real examples of by-product generation in the agri-food industry, have higher digestibility and a greater nutritional value than corn silage. These by-products showed the potential to be used in ruminant-ensiled rations and could replace part of the ingredients in conventional diets.