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In the spotlight: Less known protein sources for pigs

Prices of soybean meal and crystalline amino acids remain volatile. From time to time, there is considerable interest for less well known protein sources, either because of availability or reduced price opportunities. When such cases arise, it is important to know two key elements: antinutritional factors that need to be evaluated, and maximum inclusion rate for each class of pigs.

This information along with the nutrient profile will help the nutritionist determine the level at which such alternative protein sources can contribute in existing diets to reduce feed cost without affecting animal performance. Below is just an introduction for some common alternative protein sources. The figures suggested are for ‘educational’ purposes and should not be used without consulting first with a qualified nutritionist that knows first-hand the raw material in question and the farm/animals where they are to be used.
Rapeseed (Brassica napus and Brassica campestris), a member of the same family as mustard, cabbage and turnips, is a major oil yielding crop, being third after soybeans and palm. It is cultivated in regions with colder climates that are usually unsuitable for growing soybeans.
Regular varieties of rapeseed contain high levels of anti-nutritional factors that cause problems in all animals. These factors include glucosinolates (goitrogenic), erucic acid (toxic), tannins, sinapine, phytic acid, and mucilage. The most important for animal production is glucosinolates that reduce feed palatability due to their ‘hot’ and pungent taste (same as mustard and horseradish).As these anti-nutritional factors are not greatly affected by heat treatment, it has been only through plant breeding that their presence has been significantly reduced. Modern varieties of rapeseed that are low in glucosinolates or erucic acid are often referred to as 0-rapeseed. Those low in both glucosinolates and erucic acid are referred to as as 00-rapeseed. The latter is the most common variety used today worldwide for oil production for human consumption.
Feeding normal rapeseed meal (not double-zero)
If rapeseed with normal (higher) levels of glucosinolates and erucic acid is to be fed to pigs, then naturally, usage must be limited to avoid reduced performance and ensure animal health. Normal rapeseed meal should be used only in diets for finishing pigs (above 60 kg live weight) and gestating sows. In both cases, a maximum inclusion rate of 10% is recommended.
Feeding 00-rapeseed mealRapeseed meal from ‘double-zero’ varieties (including authentic Canadian canola) can be used more freely than normal rapeseed meal. In such cases, it is best to first limit inclusion of 00-rapeseed meal up to 25-50% of current soybean levels. In reality, this has been proven often to be the best case scenario. Although there are several research reports where 00-rapeseed meal has successfully replaced soybean meal 100%, in practice this should be avoided unless its quality is assured and diets are balanced and double-checked by a qualified nutritionist.
In more practical terms, 00-rapeseed meal may be used safely up to 5-10% in young pigs and up to 15-20% for older pigs. Well balanced diets for gestating sows can be based solely on 00-rapeseed meal as the major protein source (zero soybean meal diets). Diets for lactating sows should include no more 00-rapeseed meal than is necessary to reach the maximum crude fibre specification.
Maize gluten
Maize gluten is a by-product of the starch industry. Maize gluten meal is basically just the protein gluten, where maize gluten feed is gluten plus hulls. There are three maize gluten products available in the market today. Maize gluten meal with 60% crude protein containing no hulls. Maize gluten feed with 20% protein contains all hulls from the starch production process. And, finally, maize gluten meal with 40% protein, being a blend of the other two products, or a blend of gluten and half the hulls.
Feeding maize gluten products
Due to low energy content, maize gluten feed is best avoided in diets for piglets. On the other hand, assuming diets are properly balanced for all amino acids, including valine and isoleucine, maize gluten meal at 60% crude protein can be used up to 10% in diets for piglets. Older pigs and sows can consume diets containing up to 20% maize gluten meal, but less maize gluten feed (to the point where diets are balanced for energy and amino acids). Of course, these are general, conservative numbers. Under proper nutritional guidance, up to 30% or even more maize gluten meal/feed can be used in certain diets. Indeed, a study conducted at the University of Kentucky, USA, indicated that up to 80% maize gluten feed can be used in diets for gestating sows without any problems.
Sunflowers (Helianthus annuus) are grown mostly in cold climates for their seeds. These are used for oil production or as a confectionary item. There are distinct varieties for each use because confectionary seeds are not rich enough to be used for oil production. Sunflower meal is the residual matter after oil extraction, usually by the use of solvents (as in the case of soybeans), but also by hydraulic pressure (old method). The latter method produces sunflower meal rich in residual oil, and this should be taken into account during feed formulation.
All pigs will readily consume diets based on sunflower meal. This is due to the fact that sunflower meal contains a small amount of sugars, which give a sweet taste to pig feed. This is very important in piglet feeds where a sweet taste is often simulated by the use of artificial chemical sweeteners.
Sunflowers contain no known anti-nutritional factors, in contrast to other protein sources such as soybean meal that contains a plethora of such compounds. Nevertheless, the use of sunflower meal in pig diets is restricted by its concentration in crude fibre, something that is considered undesirable in diets for piglets, growing pigs and lactating sows – at least when crude fibre concentration exceeds 3-5% in the final complete diet.Sunflower meal is available commercially in three forms, depending on the level of hulls in the final product (see also Table 1).Dehulled sunflower meal, that contains no hulls. This has about 38% crude protein and 14% crude fibre. This is the preferred type of sunflower meal for piglet and lactation diets.
Partially dehulled sunflower meal, that contains a part of the hulls. It contains 32-35% crude protein, and 20-25% crude fibre. The exact levels depend on the concentration of hulls. This product is suitable for growing pigs and gestating sows.Standard sunflower meal, that contains all the seed hulls. Here, the crude protein concentration is usually less than 30%, with around 25-30% fibre. This product should be avoided in diets for piglets and used only sparingly in diets for lactating sows and growing pigs.
In contrast, it can be a very useful ingredient in diets for gestating sows that require a high level of crude fibre – especially for group housed sows fed ad libitum.Sunflower seeds (full fat) are often available for animal consumption after being discarded by the oil or confectionary industry for a number of reasons pertaining to their quality. Whole seeds contain about 16% crude protein, 45% oil, and 16% crude fibre. Research conducted in the 1980s has demonstrated that the high fibre content makes whole seeds equally unsuitable with sunflower meal when used in high concentrations in pig diets. But, in addition, it appears the high oil content in full-fat seeds creates further feed intake problems, related to palatability, even in cases where a high-fibre concentration was not a major concern, such as in gestating sows. Thus, it has been proposed to reduce the inclusion level of full-fat sunflower seed to 10% in piglet diets and diets for growing pigs, and to 25% in lactation and gestation diets.
Minor legumes
Fababeans (Vicia faba) are a legume related to the garden bean (those beans consumed by humans). There are two major types of fababean: those from white-flower varieties and those from coloured-flower varieties. Their chemical composition and nutritive value is about the same, but the coloured-flower varieties contain more tannins. Tannins (usally about 0.3 to 0.5%) reduce feed intake and depress digestibility of protein and energy. Other major anti-nutritional factors in fababeans include trypsin inhibitors (at levels below those found in raw soybeans) and hemagglutinins (at levels many times those found in raw soybeans).
The presence of these anti-nutritional factors make necessary the use of raw fababeans in limited levels in diets for pigs. The maximum level below which problems are few is around 15%. In diets for young pigs, this level should be 5-10%. It is possible to feed up to 20% fababeans in diets for finishing pigs, but if the fababeans are from coloured-flower varieties, feed intake will be reduced. Feeding high levels of fababeans creates a large volume of gastro-intestinal gases that cause constipation in lactating and gestating sows. In general, fababeans should be introduced gradually in pig diets starting from 5% and not exceeding 20%.Field peas (Pisum sativum) are grown mainly for human consumption, but large quantities are made available for livestock feeding due to many reasons (quality, over-production, prices, etc). Like all legumes, field peas contain several anti-nutritional factors, of which the most important are: trypsin-inhibitors, hemagglutinins, and cyanogenic glycosides, in order of importance.Nevertheless, in most cultivated varieties, these anti-nutritional factors are in such low levels that they do not pose a great level of risk when peas are fed raw, that is without any heat-treatment.
This is especially true, when inclusion levels are rather low, and the animals are either of progressed age (finishing pigs) and used to eating peas from earlier in life. In diets for piglets, the maximum inclusion rate of raw peas is 15%. Above this level, feed intake drops and growth is impaired. In some cases, higher levels can be used if digestible tryptophan levels in the whole diet are properly balanced. For growing-finishing pigs, field peas can totally replace soybean meal, as long as the diets are balanced in energy and amino acids. For breeding pigs, results are mixed, and when using varieties with high levels of anti-nutritional factors, breeding performance can be impaired when feeding more than 10% peas. In some studies, feeding up to 25% field peas did not affect reproductive performance.
Lentils (Lens culinary) become occasionally available to the animal industry, especially when they suffer from quality problems (such as frost damage, discoloration, or seed damage). Nevertheless, these issues do not pose any problems when such lentils are fed to pigs of all ages. Care should be taken when using lentils: the diets should be balanced on digestible amino acids, because not all crude protein in lentils is true protein – lentils contain about 7% non-protein nitrogen.The major anti-nutritional factor in lentils is protease inhibitors, but these are not present in sufficient quantities to depress pig performance. Thus, up to 30% raw lentils have been used with success in growing-finishing diets (Table 2). Nevertheless, in diets for very young pigs it is always prudent to use conservative levels, starting at no more than 10% in high quality formulations. PP


By Dr Ioannis Mavromichalis, international consulting nutritionist, Madrid, Spain

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