By Eduardo Beltranena, Charlotte Heyer, Lifang Wang & Ruurd Zijlstra
Editor’s note: All authors are researchers in the Department of Agricultural, Food and Nutritional Science; Faculty of Agriculture, Life & Environmental Sciences; University of Alberta. Zijlstra can be contacted at firstname.lastname@example.org.
Does extruding canola meal prior to feeding it to pigs make a difference? If you have been feeding extruded canola meal, you might like to consider whether the added cost of processing generates worthwhile benefits.
To determine the nutrient digestibility of extruded canola meal in growing pigs and assess its affect on growth performance in weaned pigs, we extruded solvent-extracted canola meal at increasing screw speeds, then fed extruded canola meal to these pigs.
In Canada, more than 20 million tonnes of canola seed is produced annually, and domestic crushing generates 4.6 million tonnes of canola meal. Canola meal is widely included in pig diets but has a lower energy value and contains less digestible amino acids (chain-linked building blocks of protein) compared with dehulled soybean meal, partly due to a greater content of water-insoluble, wood-type hull fibre that reduces the digestibility of energy and protein. This high-protein but fibrous feedstuff is a particular challenge for young pigs with immature digestive capacity.
Extrusion is characterized by a high shear force produced from a rotating screw with a narrowing flight, constricting the canola meal against the barrel and towards its exit hole, with the aid of added steam. The process is designed to disrupt the rigid cell walls of the canola seed hull and increase fibre solubility, as a result. Heat generated from the friction created by the process may cause canola proteins to break down and may also degrade glucosinolates (bitter-tasting, mustard-flavoured compounds). These bitter compounds could encourage pigs to turn their noses up to unextruded canola meal, reducing feed intake.
To measure the effects of extrusion on canola meal, we extruded dark-seeded, solvent-extracted Brassica napus canola meal at three different screw speeds and fed these meals to growing and weaned pigs in two trials conducted at the University of Alberta’s Swine Research and Technology Centre (SRTC) in Edmonton.
The canola meal was sourced from Altona, Manitoba for the growing pig trial and from Lloydminster, Alberta for the weaned pig trial. The canola meals were extruded at the University of Alberta’s Agri-Food Discovery Place, also in Edmonton, using a single-screw extruder at three screw speeds: low speed, at 250 revolutions per minute (rpm) (CM-250); medium speed, at 350 rpm (CM-350); and high speed, at 450 rpm (CM-450). As the extruder screw speed increases, so does the specific mechanical energy and the shear force, which creates higher temperatures. Extrusion temperature was set from 80 degrees-Celsius in the first zone of the barrel to 100 degrees-Celsius in the fifth zone. The unextruded and extruded canola meal were then ground using a hammer mill fitted with a 2.78-millimetre screen.
In the first trial, eight crossbred barrows with an initial body weight of 68.1 kilograms (kg) (Duroc crossed with Large White/Landrace F1 from Hypor in Regina) had a T-cannula surgically implanted at the end of the small intestine to collect the material being digested. By comparing the undigested nutrients in collected feces, we could calculate the portion of microbial fermentation in the hindgut. We fed the pigs with one of four diets containing 50 per cent unextruded or one of three extruded canola meal samples in each of the four nine-day periods. Prior to feeding the canola test diets, we fed the pigs a nitrogen-free diet without any protein sources to measure the basal endogenous losses of protein and amino acids, which is a common process when studying standardized amino acid digestibility of feed ingredients; it helps account for gut enzyme secretions or microbial contributions to protein content in the gut content found in the small intestines of pigs.
In the second trial, 200 of the same type of pigs from the first trial were weaned in three groups at 21-days-old, randomly placed in 50 pens, with two male and two female pigs per pen at heavy and light body weights. Starting two weeks after weaning, pigs with an initial body weight of 8.3 kg were fed one of five experimental diets for three weeks. The five wheat-based diets contained 20 per cent soybean meal, unextruded or extruded canola meal, and were balanced for net energy by addition of canola oil and digestible amino acids, including supplemented crystalline lysine, threonine, methionine and tryptophan. Diets did not contain antimicrobials or growth promoters. Mash diets were mixed at the University of Alberta’s feed mill in Edmonton. Pens measuring 1.1 metres by 1.5 metres with plastic slatted flooring and polyvinyl chloride partitions were equipped with a dry feeder, providing four feeding spaces and a nipple drinker. Pigs had free access to feed and water. Rooms were ventilated using negative pressure, to help the pigs maintain a comfortable ambient body temperature, with 12-hour light and dark cycles.
Short-term heating during extrusion did not cause protein damage compared to unextruded canola meal, as indicated by similar chemically available lysine content. Extrusion did not cause much change in seed hull fibre content, and it did not convert this mostly insoluble fibre to soluble fibre.
Extrusion, which may increase availability of denatured protein to the pig’s digestive enzymes, indeed increased small intestine digestibility of protein (Figure 1), digestibility of most amino acids (Figure 2) and reduced hindgut fermentation of protein. Extrusion did not affect small intestine or total tract digestibility of energy. Increasing extruder screw speed did not further alter protein and energy digestibility in growing pigs, indicating that the increased mechanical energy was not sufficient to open up the mostly insoluble fibre structure of the canola seed hull. The overall picture emerging from the present study indicates that extrusion processing at the settings applied did not disrupt the hull cell wall. However, extrusion did decrease the content of total glucosinolates by 14 per cent.
In weaned pigs, extrusion of canola meal decreased the total tract digestibility of protein by three per cent but not the energy value (data not shown). Increasing extruder speed did not further alter the total tract digestibility of protein and energy, and it did not change the digestible energy or calculated net energy. Given that canola meal contains approximately three times more insoluble fibre than dehulled soybean meal (27 per cent versus 8.5 per cent fibre), diet nutrient digestibility of extruded canola meal was upwards of six per cent lower than that of soybean meal.
Extrusion of canola meal did not affect feed intake, body weight gain or feed conversion in weaned pigs for the entire trial (Figure 3). Increasing extruder screw speeds linearly increased body weight gain in the first week and improved feed conversion for the entire trial.
Because we balanced the diets for equal net energy and several important amino acids, pigs fed diets with extruded canola meal did maintain feed intake and had similar body weight gain and feed conversion compared with pigs fed dehulled soybean meal diet for each week and the entire trial.
These results suggest the importance of adopting the net energy system for diet formulation of high-protein, fibrous feedstuffs like canola meal. As shown in growing pigs, extrusion somewhat increased the availability of amino acids; however, this increase in amino acids supply did not increase growth performance in weaned pigs.
Our study confirms that extrusion of dark-seeded, solvent-extracted Brassica napus canola meal increased small intestine digestibility of most indispensable amino acids in growing pigs, which provided to the pigs slightly more available amino acids from the canola meal. However, increasing extruder screw speeds and mechanical energy did not increase energy digestibility in growing pigs and did not improve growth performance in weaned pigs. Extrusion processing, considering its added cost, did not show benefits on growth performance of weaned pigs.
Funding for this project was provided by the Canola Cluster, sponsored by Agriculture and Agri-Food Canada and the Canola Council of Canada. Heyer acknowledges funding from the German Research Foundation.