Alternative by-products to replace soy in pig feed

Factors including the physical and chemical characteristics of the alternative sources, the level of essential amino acids, the presence of antinutritional factors, and the method of conversion into final products are essential in evaluating potential soy substitutes.

Alternative by-products used in pig diets include:

  • oilseed by-products,
  • local vegetable by-products,
  • by-products of industrial processes, e
  • processed animal protein by-products.

Oilseed by-products

Oilseed by-products (including meals, sweets and cakes) are derived from oily plant species. The defatted byproducts of flaxseed and sesame include high volumes of crude protein. Rapeseed meal obtained from the press cake left after oil extraction contains 35% protein and high fiber content, sulfur-containing amino acids and phosphorus. However, rapeseed meal consists of anti-nutritional factors such as glucosinolates, tannins and phenols which limit its application in pig diet up to 15%. However, canola flour derived from a variety of canola seeds is low in erucic acid and glucosinolates, making it a potential candidate for soy replacement.

Local vegetable by-products

Minor local plants such as guar can be used as a substitute for soy. Guar flour is a by-product of guar gum production containing highly viscous non-starch polysaccharides such as galactomannan polysaccharide which improves digest viscosity, prevents intestinal enzymatic activities and decreases nutrient digestibility.

By-products of industrial processes

Dried grains from instant stills are the major by-products of the ethanol industry produced by dry mill ethanol plants. Dry cereals from distillers with solubles are an adequate source of protein (25-30% dry matter), fat, fiber and energy for pig diets. Furthermore, they are used significantly in pig diets due to the encouraged use of renewable energy sources for biofuel production. Furthermore, the dried grains with soluble distillers have easily digestible protein characteristics, low content of anti-nutritional substances and high nutritional values. However, they are rich in unsaturated fatty acids which may adversely affect dietary intake and oxidative stability of the by-product. The byproduct of rice stills is another good source of crude protein; however, its high fiber content limits its use in pig diets.

Processed animal protein by-products

The major processed animal proteins used in pig diets include:

  • meat and bone meal,
  • blood products,
  • inedible meat,
  • waste tissue and animal fat,
  • feather flour,
  • poultry by-product meals e
  • fishmeal by-products.

Additionally, liquid whey residues from the dairy industry can be used as dry ingredients. Fish silage has a high protein content (39.01%), a high protein digestibility (93.58%) and a high biological value. However, due to its high moisture content, high price, and limited availability, its application in pig diets has declined.

Effects on growth performance and carcass characters

  • Inclusion of rapeseed meal in pig diets – decreases feed intake due to the presence of glucosinolate which reduces the goodness of the diet. The different inclusion levels of rapeseed meal in the growing and finishing periods had no significant effect on the mean daily gain and feed conversion ratio, demonstrating the flexibility to use this protein source alone or in conjunction with other sources. Furthermore, rapeseed flour can be added to other legumes instead of soybeans; however, synthetic amino acids must be added to the blend to balance out the nutritional quality. Although there are conflicting results regarding the impact of rapeseed meal on growth performance due to the differences in glucosinolate concentrations in each rapeseed variety. Furthermore, rapeseed flour contains high amounts of anti-nutritional factors in the variety used. On the other hand, the inclusion of canola meal has no impact on carcass traits, including seasoning rate, backfat thickness, lean content, weight, carcass yield, and cut composition. .
  • Inclusion of guar flour in pig diets – decreases the average daily feed intake, average daily gain and feed conversion ratio.
  • Defatted rice bran – has negative effects on performance with an increase in feed intake and a decrease in the average daily gain and feed conversion ratio; however, it has no impact on carcass quality.
  • Add the fishmeal – decreases daily feed intake, daily weight gain and feed conversion ratio. Additionally, the inclusion of fishmeal reduces backfat thickness, loin depth, and fat depth.

Effects on meat quality traits

  • Total replacement of soybean meal with rapeseed meal – affects the chemical composition of different cuts of pork, reducing the fat content of the shoulder and steak, while increasing the fat content of the ham and bacon. However, the total replacement of soybeans with canola had no effect on the stability of the pork during storage.
  • Dried corn distiller grain with soluble – has a high content of unsaturated fatty acids which negatively affects the quality of the meat and decreases the protein content.
  • Fava beans as a partial replacement for soy – increases the tenderness, juiciness and palatability of the meat; however, the flavor is not affected.
  • The inclusion of yellow lupine – in the diet causes lower smell, taste and juiciness scores.
  • Dried Corn Stiller Grain – improves tenderness and juiciness of meat and fishmeal silage decreases toughness and overall acceptability of meat.

Concluding remarks

Traditionally, soy has been the main source of protein in pig diet formulations; however, soybean application has been limited in recent years due to rising prices, ethical issues, environmental impact, and competition for land use. Various by-products, including oilseed by-products, local plant by-products, industrial process by-products, and processed animal protein by-products are among potential soybean substitutes. However, more research is needed to evaluate their cost-effectiveness and effects on meat properties.

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