Editor’s note: This article is based on a paper authored by Mian Riaz, Chris Mack, Akram Haq and Chris Bailey, researchers at Texas A&M University.
The utilization of raw and/or heat treated soybeans as a feed material for terrestrial animals has been intensively studied for many years. Full fat soybean meal (FFSBM) is obtained after the extrusion of whole soybean, considered an excellent source of energy and protein in poultry feed. It is widely available and is a useful raw material because it contains approximately 18% soybean oil, which contains over 50% linoleic acid (Table 1).
Linoleic acid is an essential fatty acid and is required to be a part of poultry diet. It has been proven that diets containing extruded FFSBM yielded excellent results when compared with control diets based on soybean meal and animal fats.
Protein is the major nutrient of soybeans and is ranked second after oil in terms of economic value. Roasted soybean and dehulled solvent-extracted soybean meal contains approximately the same essential amino acid composition when expressed in percentage of crude protein. Soybean protein is particularly valuable because it has one of the best amino acid compositions among plant proteins.
Although oil and protein are components of major interest, FFSBM contains a substantial amount of carbohydrates, and these are approximately 30% on a dry weight basis. The carbohydrate fraction of soybeans is usually classified in two categories: the soluble carbohydrates or oligosaccharides, and insoluble carbohydrates or polysaccharides.
Applying an exogenous enzyme mainly composed of α-galactosidase is an alternative to alleviate the detrimental effects of the saccharides. Researchers at Texas A&M University recently conducted a study to evaluate whether the α-galactosidase enzyme added in FFSBM after extrusion or during extrusion improves the bioavailability of energy and nutrients of poultry diets. The main objective was to find out the effects of enzyme treated feed on weight gain, food conversion ratio and total metabolized energy (TME) of poultry.
Materials and methods
Whole soybeans were obtained from a farm in Texas and evaluated for their composition. The single screw dry extruder (Insta-Pro Jr 600) was used to extrude whole soybeans. The extruder barrel temperature was maintained at 140 degrees C while the feeding rate was 100 kilograms (kg) per hour. Enzyme α-galactosidase (ENZECO) was obtained from the Enzyme Development Corporation, used with a ratio of 0.015% (49 gm) on one batch (32 kg) of soybeans during extrusion and on second batch after extrusion. One batch of FFSBM without enzyme application was also produced and used as a control.
All the extrusion and related processing activities were performed in the pilot plant of Food Protein R&D Center, Texas A&M University.
One basal industry type broiler starter diet was prepared using corn excluding soybean meal. The basal diet was divided into three equally-sized batches. To each batch, extruded whole soybean (FFSBM) was added with or without a-galactosidase to complete the diet.
For the three-week study, approximately 200 one-day-old broiler chicks were purchased having breed/strain of Cobb/Ross with a straight run sex. At the hatchery, the birds received routine vaccinations. All 200 broiler chicks were distributed among one Peterson battery brooder units (24 pens; five birds per pen). A total of three treatments were randomly assigned to pens such that each treatment was represented at least once for any given vertical row of pens.
The brooder room was air conditioned and 24-hour lighting was provided. Each brooder pen contained a heat lamp for supplemental heat as required. The pen was the unit of measure for the performance phase of this experiment. Bird weights (g) by pen were recorded at the study initiation and weekly thereafter over a 21-day experimental period.
Weekly feed consumption, body weight gain and feed conversion ratio (feed/gain) were determined at the end of each week. Daily observations were made with regard to general flock condition, temperature, lighting, water, feed, litter condition, unanticipated events for the house and mortality for each pen.
A total of 15 three-week old broilers were individually housed in wire cages in a windowless room where they received 24 hours of light daily. Birds were divided into three groups (five birds per group). Each group was tested for one of the test diet (no enzyme, enzyme added during extrusion or enzyme added after extrusion). Birds were deprived of feed for 30 hours. At 12 and 24 hours after feed withdrawal, all birds were tube-fed 15 grams of glucose (dissolved into 30 ml of distilled water) and were allowed to void the contents of their GI tracts for a period of 36 hours.
At 36 hours after feed withdrawal, all roosters were tube-fed 15 grams of glucose solution. At this point, excreta from individual birds were collected for a period of 36 hours in order to determine endogenous nitrogen loss for each bird. During this period, every 12-hour interval, each bird was tube-fed 15 grams of glucose. Following endogenous excreta collection, each bird was offered a known amount of one of the test diet and excreta collection trays were placed to collect test diet excreta. At 12 and 24 hours after feed withdrawal, all birds were tube-fed 15 grams of glucose and were allowed to void the contents of their GI tracts for a period of 36 hours.
During both the endogenous excreta and the test ingredient excreta collection, stainless steel collection trays were placed under each cockerel for a period of 36 hours. The total volume of excreta was collected, taking care to exclude inclusion of feathers, scale, and other debris from the collected sample.
All excreta samples immediately were dried at 85 degrees C for 24 hours in a forced draft drying oven. Just prior to bomb calorimetry, dry matter content for test diets and excreta samples was determined by drying the samples at 105 degrees C for 24 hours in a forced draft drying oven. Energy content of the test diets and excreta was determined by bomb calorimetry in a Parr Adiabatic bomb calorimeter.
Addition of α-galactosidase enzyme in FFSBM affected the weight gain of birds. Enzyme was added with the ratio of 0.015% in FFSBM, after that 50% of this FFSBM was used in the final
Results conclude that birds fed the diet treated with enzyme after extrusion gained more live weight (825 grams) than the birds fed diets with no enzyme (818 grams) or on diets in which enzyme added during extrusion (816 grams). However, these effects were not statistically significant. A noticeable difference was observed in the body weight of birds during the different stages of feeding trials but this difference in weight gain was also not statistically significant.
In the first two weeks, maximum weight gain was observed in the birds which were fed on the diet with enzymes while in the third week the birds fed on the diet with enzymes added during extrusion gained the maximum weight. Therefore, an obvious effect occurred before day 15 of the feeding periods, but all these effects were statistically non-significant. In a similar study which was conducted by using soybean meal 48% with the same proportion in the diet instead of FFSBM, the mean body weight of birds after three weeks was 600±48 grams. But by using FFSBM and α-galactosidase, it went up to 825±48 grams in same time period. This was due to the presence of the high quantity of oil in FFSBM.
These results are similar with the finding of Creswell and Sooksridang (2009), which conducted a series of trials in which broilers were fed FFSBM. That trial concluded that birds fed on diets containing FFSBM had a higher weight gain and better feed conversion rate (FCR) than those fed with diets not containing FFSBM.
The primary function of α-galactosidase is to hydrolyze the oligosaccharides like raffinose and stachyose in SBM. Non-ruminant animals lack α-galactosidase, and therefore there is little or no hydrolysis of α-galactosidase in the intestines of the chicken. Anti-nutritional effects of α-galactosidase result from fermentation in the hindgut with the generation of hydrogen and other gases resulting in flatulence and possibly fluid retention and changes in osmotic pressure in the gut.
Trials in which birds have been fed diets with α-galactosidase enzyme in an attempt to improve the use of these oligosaccharides have demonstrated variable results.
FCR of feed with the enzyme added after extrusion was higher than that of the other two treatments, but the difference was not significant (see Table 2). The trend of FCR was not uniform throughout the trial in all three weeks, but the difference in all treatments was not significant at any stage of their growth. It can be concluded that by adding more quantity of enzyme in the feed, FCR can be increased; hence the broiler feed contained only 0.0075% of α-galactosidase enzyme because in the final feed 50% of the enzyme was used.
Some previous studies indicate that broilers fed diets containing 112 grams of α-galactosidase per tonne had improved feed conversion by four points, while in the current study 75 grams of enzyme was used in one tonne of feed, which could be one factor of reduced FCR. The addition of α-galactosidasemixed FFSBM in the feed mixture had an effect at TME that does not coincide with the weight gain by using the same feed. In this trial, TME was not significantly different (Table 3) between all three treatments. TME for untreated feed was numerically higher as compared to enzyme-treated feeds. These results are contrary to the previous study in which it is mentioned that adding α-galactosidase enzymes to SBM, irrespective of the method used to apply the enzymes, increased TME.
Addition of α-galactosidase enzyme in FFSBM after extrusion and use of this FFSBM in broiler feed had an affect on the weight gain, FCR and TME. Broiler fed on this diet gained more live weight than the other broilers which were fed on other diets. However this gain in live weight was not statistically significant.
Similarly, FCR increased for the enzyme-treated FFSBM but the differences were not significant again. The TME was also not statistically different between all treatments and better results could be obtained by doubling the quantity of enzyme in feed.