Using pulses as alternative ingredients in poultry feed

Soya UK | Narrow leaf (blue) lupin, Lupinus angustifolius, in flower and pods

Beyond soy, there is potential for leguminous plants to supply protein in diets for laying hens.

Fluctuations in the price and availability of imported ingredients for feed have a marked effect on the overall cost of egg production. Poultry nutritionists continue to look at alternative ingredients for both economic and environmental reasons. Pulses, the seeds produced by leguminous plants, are one of these ingredients.

Protein-rich leguminous plants are grown in most parts of the world. Peas, beans and lupins are fed to hens aside from soybeans. When grown locally, pulses have the potential to improve the sustainability of the industry.

However, limits are imposed due to their anti-nutritional factors and non-starch polysaccharides (NSP) enzymes, but processing and enzymes can help to improve their value.

This article offers an overview of how these pulses are used in the poultry industry.

Peas and beans

Varieties of field pea are grown throughout Europe, where they have been traditionally used in a variety of animal feed. Chickpeas are a valuable legume crop with the highest production and consumption in India. They are also important in Asia, Africa, the Americas and Mediterranean countries. Peas have moderate to high levels of starch; have relatively low levels of soluble NSP; and are a good source of arginine. However, they do contain trypsin inhibitors.

Species of bean grown for livestock feed include: field beans, mung beans and lab lab. Beans have higher tannin and alkaloid levels than peas as well as lower levels of sulphur amino acids.

Peas and beans have both been traditionally used in poultry feed and, lately, as an alternative to soybeans. Although lower in oil and protein, they are a useful source of protein and energy. Results from scientific studies suggest that no more than 10 percent of unprocessed peas or beans can be included in mash diets for laying hens without reducing egg production.

Lupin qualities

Australia is the biggest producer of lupins. They are also grown in significant quantities in France and Russia. Lupin meal contains between 32 to 38 percent protein; has virtually no starch; and is largely free of trypsin inhibitors, lectins and saponins.

A number of varieties of lupin are grown commercially including: L. albus, L. luteus and L. angustifolis. They are higher in both protein and oil to peas or beans, with a good amino acid profile. Lupins have been used in ruminant diets for many years but have become the subject of monogastric research more recently.

The "sweet," low-alkaloid types are most interesting for poultry production. Experiments on narrow leaf and yellow lupins at IBERS Aberystwyth University showed that a 15 percent protein replacement had no impact on laying hen performance.

Anti-nutritional factors and NSP

There are four main types of anti-nutritional factors (ANF) found, to a greater or lesser extent, in different varieties of peas, beans and lupins. Tannins can reduce palatability and form indigestible compounds in the gut. By reducing the activity of a protein-digesting enzyme, trypsin inhibitors reduce growth rate and feed efficiency. Alkaloids have a wide range of negative effects on poultry. Plant lectins may bind to the gut wall, reducing enzymatic activity and absorption of nutrients.

Soluble NSP may be a cause of concern when pulses are fed to laying hens. High levels of soluble NSP are associated with increased gut viscosity and decreased enzymatic activity. Insoluble NSP may have a high water binding capacity, which results in a faster gut transit time.

Processing enzymes

Dehulling involves the mechanical removal of the outer husk of pulses, where a large proportion of the ANFs are found. Up to 30 percent of lupin grain is hull, so, if removed, there is a significant increase in protein content, but at an additional cost.

Micronization, a form of "cooking" using infra-red radiation, heats feed materials uniformly and at a lower temperature than other methods. This reduces the risk of degrading important nutrients by "over-cooking." Micronization disrupts pulses' cell walls, improving digestibility and reducing the effect of ANFs. Micronization has been shown to fragment insoluble NSP, resulting in increased gut transit times. Although the process adds 15 to 20 percent to the cost, this should be offset by the improvement in nutritional value.

In a trial egg production, feed conversion and egg mass output were similar for layers fed diets containing micronized peas and those fed the wheat-soybean control diet. Except for daily feed intake, which was reduced (P < or = 0.05), dehulling did not affect (P > or = 0.05) the feeding value of peas. Researchers completely replaced soybeans with dehulled and micronized fava beans. Egg production and quality were the same. As for the control, only feed intake and yolk color were affected. 

Processed lupins

In another study, laying hens were fed diets containing either 180 g/kg of sweet lupin, 300 g/kg of pea (both dehulled and micronized), or 150 g/kg of soybean meal. Egg production and quality were comparable between the diets -- although feed conversion ratio (FCR) increased.

There is potential for the addition of enzymes to improve the nutrient availability of diets containing peas, beans or lupins, which allow for greater inclusions. Amylase, betaglucanase and xylanase have been used, with benefits seen in the degradation of starch and/or NSP. Proteases improve amino acid digestibility and reduce ANFs; while pectinases help to release energy. A combination of enzymes could increase the amount of protein and energy that pulses contribute to rations.

Commercial application

For nutritionists, price and availability are the main difficulties when formulating with pulses. Unless there are regular supplies at a competitive price, feed companies don't want to commit to their inclusion - and, without commitment, growers are reluctant to plant more. 

In terms of ANFs, beans need to be heat treated. Both could make a more regular appearance in formulations in the form of an extruded protein product (50:50 ratio, canola to peas or beans), which is already common in broiler diets. When using pulses, the latest enzyme technology is another way to improve confidence in performance. Plant breeding could also play a role by producing varieties with less ANFs, which can be grown in a variety of conditions.

While there is great potential for pulses to be included in laying hen diets, more research is needed to determine how to best to use them. If more legumes were used, there would be a demand for companies to provide them, and pressure to improve agricultural sustainability may increase funding. In France, for example, there is a subsidy for growing protein crops. 

Aside from further increases in the cost of soybeans, finding a consistent source is still an issue in many regions, but desire from the industry is needed to make peas, beans and lupins valued protein source.

 

Environmental benefits of legumes

Leguminous plants have nodule-bearing roots containing nitrogen-fixing bacteria. The seeds they produce are known as pulses and are used as a source of protein for both humans and animals. Farmers benefit from growing legumes due to reduced fertilizer requirements. This is where locally grown pulses environmental credentials are realized: improving overall sustainability of the sector.

About Author: Zoe Kay is an independent consultant providing technical services to the animal health and nutrition industry.