*John H. Goihl is president of Agri-Nutrition Services Inc., Shakopee, Minn. To expedite answers to questions concerning this article, please direct inquiries to Feedstuffs, Bottom Line of Nutrition, 7900 International Dr., Suite 650, Bloomington, Minn. 55425, or email [email protected]
THE greatest cost in animal production is feed, and the recent increase in the cost of traditional feed ingredients, because of greater competition from both the human food and biofuel industries, has increased the need for cost-effective alternative feed ingredients.
Corn and soybean meal represent two major feed ingredients in animal diets to meet the animal's protein and energy requirements. However, in the future, the swine and poultry industries may not be able to afford to continue to use large quantities of corn and soybean meal in diets.
Biofuel production has shown promise as an alternative energy source to replace oil. The first generation of liquid biofuels was obtained primarily from corn and other crops that produce sugar and vegetable oils. The second generation will use lignocellulosic biomass or woody crops as feedstocks to produce biofuels. Microalgae appears to represent the third generation, but that also could be used as an alternative feed ingredient to replace corn and soybean meal in swine and poultry diets.
Microalgae may be the alternative feedstock for improving the sustainability of animal agriculture to feed an increasing world population without exacerbating the environmental impact.
Microalgae is gaining popularity as a feedstock because of its rapid growth rate, rich oil content, strong ability to sequester carbon dioxide and rapid conversion of carbon dioxide into a reusable gas such as methane or hydrogen.
Cornell University researchers S. Gatrell, K. Lum, J. Kim and X.G. Lei reviewed the potential of defatted microalgae from the biofuel industry to provide protein and energy, replacing corn and soybean meal in swine and poultry diets.
Defatted microalgae biomass contains significant amounts of protein, carbohydrates and other nutrients after oil extraction.
Four sources of microalgae were studied, including defatted diatom microalgae biomass (DFA), whole-fat diatom microalgae biomass (WFA), defatted green microalgae biomass-1 (DGA-1) and defatted green microalgae biomass-2 (DGA-2).
The crude protein content of various species of algae ranges from 6% to 71% on a dry matter basis. The researchers used algae with a crude protein range from 13.9% to 38.2% on a dry matter basis. It was also noted that approximately 10% of the nitrogen found in microalgae consists of non-protein nitrogen, which includes nucleic acids, amines, glucosamides and nitrogen-containing cell wall components.
The amino acid profile of the four microalgae species compared favorably with conventional vegetable protein sources. The analyzed lysine content ranged from 0.57% to 2.27%. The two green microalgae had higher levels of the amino acids methionine, threonine and tryptophan.
The crude fat levels of the four microalgae sources ranged from 1.5% to 9.3%.
The marine microalgae contain greater amounts of omega-3 fatty acids (docosahexaenoic acid and eicosapentaenoic acid) compared to animal protein sources. Microalgae also contain naturally occurring carotenoids that may assist in omega-3 fatty acid stabilization.
All four microalgae sources contained a very high level of sodium (Figure) and higher levels of phosphorus compared to corn. The two diatom sources also contained higher levels of calcium and ash than soybean meal.
The information on using algae in animal diets is limited but has been investigated for decades. It is estimated that approximately one-third of the current world supply of algae is used for animal feed. The Cornell researchers conducted several studies to determine the effects of incorporating defatted microalgae biomass in diets of weanling pigs, broilers and laying hens.
Their objectives were to answer:
* Is it nutritionally safe?
* Is it physiologically safe?
* What is the maximum usage level?
* What is the effect on growth performance and the quality of animal products?
The first pilot study with weanling pigs ran for six weeks. The results showed that 6.6% of WFA or 7.2% of DFA, directly replacing soybean meal, had no negative effects on bodyweight gain or overall health status.
In another six-week study with weaning pigs, the pigs were fed up to 15% DFA to replace a combination of soybean meal and corn. The results showed that average daily gain and gain:feed were significantly reduced, but there were no differences in average daily feed intake and no signs of toxicity.
The diatom microalgae used in these studies contained 45% ash and was high in sodium and silica.
In the broiler study, replacing either 7.5% soybean meal alone or a 10% mixture of corn and soybean meal with DFA resulted in decreased bodyweight gain and feed efficiency during weeks 0-3, but not during weeks 3-6 or the entire six-week feeding period. This growth depression was due to a deficiency of essential amino acids. The high ash content of the microalgae may also increase water intake and excreta volume.
During an eight-week experiment, it was feasible to include 7.5% DFA plus amino acids in the diets of laying hens to substitute for soybean meal or for a combination of corn and soybean meal without having adverse effects on hen health or egg production. Also, there was no significant effect on egg weight, shell strength or shell specific gravity.
Microalgae may provide specific nutrient enrichments for practical application to both animal and human nutrition, including iodine and iron, omega-3 fatty acids and carotenoids. Soybean meal and microalgae produce 721 g and 135 g of carbon dioxide equivalent per kilogram, respectively, which reduces the greenhouse effect when using microalgae in place of soybean meal.
The Bottom Line
Previous research with algae and the results of these studies show that defatted microalgae biomass may serve as a viable and healthful alternative feedstuff.
When the production of microalgae becomes cost effective for biofuel production, the defatted microalgae biomass could potentially spare the use of soybean meal and corn in swine and poultry diets.
J. Anim. Sci. Vol. 92, No. 4.