Soybean Replacement by Alternative Protein Sources in Pig Nutrition and Its Effect on Meat Quality

SIMPLE SUMMARY: Soybean is the most common feed ingredient to supply protein to pigs. However, its production is linked to several issues related to environment (e.g., deforestation, water waste), production and transportation costs, as well as to ethical aspects including feed/food competition for land. In recent decades, research has endeavored to find alternatives to soybean in livestock feeds, especially for pigs. However, replacing this ingredient partially or totally may have consequences for animal growth rates, carcass yield and meat quality. The aim of this work was to review the research carried out in the last 10 years on this topic, identifying the alternative protein sources and their effects on pigs’ growth, carcass yield, and meat quality. Most of the ingredients recently studied are vegetable resources, especially local species of legumes well-adapted to specific climatic conditions. Moreover, some studies evaluated, as protein sources, oilseed by- and co-products, distillers’ dried grain with solubles, fish and animal proteins, and other co-products derived from other supply chains. Among innovative protein sources, microalgae and insects are gaining attention. ABSTRACT: Soybean is one of the most expensive and limiting feed ingredients in diet formulations; however, in pig farming, it represents the main source of protein. The production and supply of soybean are critical steps due to their environmental impact and feed/food competition for land use. Therefore, research is focusing on finding alternatives to replace soybean partially or totally. However, alternative ingredients should ensure similar growth performance, carcass traits, and meat quality characteristics compared to conventional soybean-based diets. The objective of this review was to evaluate the impact of different alternative protein sources to soybean in pig nutrition and their effects on growth performance, carcass, and meat quality traits. The review process was performed on Scopus(®), and it considered research findings published from 2012 to the present on the Sus scrofa species. Articles without a control group fed with soybean were discarded. The main alternative protein sources identified were other legumes and distillers’ dried grain with solubles (fish and animal proteins, oilseed by- and co-products). Interesting innovative protein sources included by-products from other industries (residues), microalgae and insects. Nevertheless, in dietary formulations, close attention must be paid to address the nutritional requirements, balance the supply of amino acids, avoid anti-nutritional or toxic compounds occasionally present in alternative protein sources, as well as determine the availability of protein feed in specific geographical areas.