By Muhammad Ali, DVM
PhD student
Department of Poultry Science, University of Georgia
Emerging evidence suggests that diets high in oleic acid (HOA) offer significant benefits for human health.1 One potential source of this beneficial fatty acid could be meat from broilers fed with full-fat, HOA soybeans.
There is evidence that broiler meat can be enriched with HOA from sources such as peanut meal and oils, but research in broilers with HOA soybeans has been limited. This dearth of research coupled with the theory that providing HOA from soybeans might have advantages for poultry as well as people was the impetus for a series of studies at North Carolina State University when I was working toward my master’s degree.
The studies were conducted under the direction of Edgar Oviedo, PhD, and Michael Joseph, PhD, and in collaboration with the USDA-ARS scientists led by Ondulla Toomer, PhD.
Versatile protein
Soybean is a versatile protein source frequently used in poultry diets. Soybean meal is obtained after oil extraction using a solvent. In contrast, full-fat soybeans maintain the bean oil content.
Regular soybean oil has a high polyunsaturated fatty acid (PUFA) concentration, and PUFAs, when ingested by humans, are associated with a decreased risk of chronic diseases such as diabetes and cardiovascular disease.2 However, if ingested in large amounts, omega-6 PUFAs, such as linoleic acid, can be pro-inflammatory, which may be undesirable for human health.3 In addition, PUFAs are more susceptible to oxidation, which reduces shelf and fry life.
Soybeans with HOA, developed by plant geneticists, have a more favorable lipid profile compared to ordinary soybeans. More specifically, HOA soybeans have >75% oleic acid and about <1.5% linoleic acid compared to 18% oleic acid and 55% linoleic acid for ordinary soybeans.
Study 1: Effect on breast-meat fatty acid profile
In the first study, we raised 540 broilers till 47 days of age and evaluated the effects of a full-fat HOA soybean in a balanced broiler diet on the fatty acid profile of breast meat.
When broilers were processed at 48 days of age, breast-meat analysis from birds that received the HOA soybean diet had 54% to 86% more oleic acid content and a linoleic acid reduction of 42% to 57 % compared to breast meat from broilers fed a normal oleic full-fat or normal oleic-extruded expeller soybean diet.
The meat content of other monounsaturated fatty acids like palmitoleic acid and erucic acid was also higher in the HOA group, with a reduction in saturated fatty acids such as myristic acid and margaric acid and polyunsaturated acids such as linoleic acid.
Broilers fed the HOA diet had a reduced feed-conversion ratio throughout the entire study, but no difference was observed among study groups for bodyweight gain, feed intake, cut-up parts yield or visceral organs.
Study 2: Amino acid digestibility
Digestibility is the difference between the amount of feed ingested and the amount of excreta produced, and it is important to evaluate the quality of ingested nutrients. Although full-fat, HOA soybeans can improve the fatty acid profile of breast meat, it’s important to also know whether they are easily digested because the digestibility of amino acids is crucial for precise feed formulation.
Here again, there has been little research, so in our second study, we determined the apparent ileal digestibility (AID) and standard ileal digestibility (SID) values. During protein fermentation in the hindgut, some amino acids may be produced that the host cannot utilize. So, ileal digestible amino acids present a better picture of the amino acids available to the broilers.
In the second experiment, the same starter diet was given to all the chicks for the first 14 days. Test diets were provided during the next 9 adaptation days. We also fed a nitrogen-free diet (NFD) to a separate group of broilers to calculate the basal endogenous losses, which are the natural or inherited losses of nutrients occurring within the digestive tract regardless of dietary intake (e.g., mucus, bile secretions and sloughed-off epithelial cells). It is worth mentioning that basal endogenous losses are included in the AID calculation, but in SID, they are deducted from AID.
An NFD is a diet without any protein or amino acid. For this experiment, the diet was formulated using corn starch and dextrose. Testing soybean products was included in the NFD.
The test diets contained 57.5% of basal NFD and 42.5% of each testing soybean source. Titanium dioxide was used as an inert marker. Later, ileal digesta was collected to analyze and calculate AID and SID values.
Our results revealed that the AID and SID of high-oleic full-fat soybeans were nearly similar to those of a commodity full-fat soybean source. However, these values were less than solvent-extracted and extruded expeller soybean meal.
Study 3: Metabolizable energy values
While soybean is mainly used for protein content in broiler diets, it also contributes 20% to 30% of the metabolizable energy. The importance of determining the energy content is evident from its role in feed consumption, broiler growth, feed utilization efficiency, carcass traits and feed formulation costs.
No data on apparent metabolizable energy (AME) and AME corrected for zero nitrogen retention (AMEn) of full-fat HOA soybeans was available. Therefore, in a third study, we determined the AME and AMEn of a full-fat HOA soybean as compared to solvent-extracted, normal oleic full-fat, and normal oleic extruded expeller soybean meal.
We determined these values using the difference method. In this method, a reference or basal diet is prepared that is complete and nutritionally balanced, and ingredients to be tested are included in the basal diet at different levels to prepare assay diets. We did experiment with a 30% inclusion of test ingredients using a corn-soy reference diet with two collection techniques (partial and total excreta collection). In both collection techniques, the AME and AMEn values of full-fat HOA soybean were higher than solvent-extracted soybean meal and normal oleic extruded expeller soybean meal but nearly identical to normal oleic full-fat soybean. Additionally, the total collection method gave higher energy values for all testing soybeans than the partial collection method.
Applications and benefits
Full-fat, HOA soybeans have numerous potential benefits for poultry production. HOA soybean oil has a longer shelf life. Using full-fat soybeans can save on the cost of mixing other vegetable oils when economically feasible.
Changing the fatty acid composition of chicken meat with full-fat HOA soybeans may reduce lipid oxidation in fresh chicken meat.4 In contrast, an elevated level of PUFAs can produce “soft fat,” making it more vulnerable to lipid oxidation. The decrease in lipid oxidation can benefit both vendors and buyers of poultry meat.
Full-fat HOA soybeans are an excellent product for organic and health-focused poultry markets and would have premium pricing.
Moreover, scientific evidence indicates that diets enriched with monounsaturated fatty acids can positively affect human cardiovascular health. These diets can lower low-density lipoprotein cholesterol without lowering high-density lipoprotein cholesterol in blood plasma.5 Furthermore, it helps by reducing the susceptibility of low-density lipoprotein to oxidation.6
Acknowledgments
I want to acknowledge my colleagues at NC State University: Maria Alfaro-Wisaquillo, Gustavo Quintana-Ospina, Lina-Maria Peñuela-Sierra and Danny Patino, and USDA-ARS scientists Dr. Lisa Dean, Rouf Mian, Earl Taliercio and Thien Vu.
For further readings about these experiments, please check the following links:
https://doi.org/10.1016/j.psj.2023.103399
https://doi.org/10.1016/j.psj.2023.103152
https://doi.org/10.1016/j.psj.2023.103408
References
1 Lichtenstein AH, Matthan NR, Jalbert SM, Resteghini NA, Schaefer EJ, Ausman LM. Novel soybean oils with different fatty acid profiles alter cardiovascular disease risk factors in moderately hyperlipidemic subjects. Am J Clinic Nutri. 2006;84(3):497-504.
2 Kris-Etherton PM, Hecker KD, Binkoski AE. Polyunsaturated fatty acids and cardiovascular health. Nutri Rev. 2004;62(11):414-426.
3 Mercola J, D’Adamo CR. Linoleic acid: a narrative review of the effects of increased intake in the standard American diet and associations with chronic disease. Nutri. 2023;15(14):3129.
4 Rebolé A, Rodríguez ML, Ortiz LT, Alzueta C, Centeno C, Viveros A, Brenes A, Arija I. Effect of dietary high-oleic acid sunflower seed, palm oil and vitamin E supplementation on broiler performance, fatty acid composition and oxidation susceptibility of meat. Brit Poult Sci. 2006;47(5):581-591.
5 Lichtenstein AH, Matthan NR, Jalbert SM, Resteghini NA, Schaefer EJ, Ausman LM. Novel soybean oils with different fatty acid profiles
6 Roche HM. Olive oil, high-oleic acid sunflower oil and CHD. Brit J Nutri. 2001;85(1):3-4.
