Glycerin is a byproduct of biodiesel production. It is estimated that during 2007, 41 million gallons of glycerin resulted from the production of 450 million gallons of biodiesel. Glycerin represents approximately 9 percent of the output of the transesterification process although the product must be refined to remove methanol and water.
Generally, glycerin is well absorbed and subsequent metabolism releases energy via glycolysis in the Krebb cycle and derived glucose can be used for gluconeogenesis and lipid formation. A definitive study was conducted to determine the metabolizable energy content of glycerin for laying hens.
A basal diet was supplemented with 5 percent, 10 percent or 15 percent glycerin, replacing glucose. Experimental hens were 48 weeks of age. Commercial glycerin varies considerably in composition as evidenced by a wide range of color and moisture content. The AMEn values range from 1,326 to 3,688 kcal/lb. Glycerin from animal fat has an AMEn value of 2,741 kcal/lb compared to the ingredient derived from soy oil (1,839 kcal/lb) or from yellow grease at 3,175 kcal/lb.
These differences were attributed to the residual fatty acids in the glycerin samples evaluated. The glycerin source used in the evaluation assayed at a fatty acid content of 0.29 percent, with 9.6 percent moisture and 7 percent glycerin. The ingredient provides only calories in contrast to animal fats or natural vegetable ingredients. Flowability is a major problem and it was considered that a 5 percent inclusion represented the maximum to avoid bridging. On the basis of current ingredient costs, liquid glycerin is worth only 5 cents per pound compared to a commercial price of 20 cents per pound. The ingredient must be heated for acceptable handling and mixing. Based on the extreme variability in AMEn and the nutrient contribution to a conventional hen diet, glycerin is not an attractive ingredient and will have little contribution to feeding of flocks producing eggs.
Dried Distillers Grains with Solubles
Professor Sheila Scheideler of the University of Nebraska in association with Dr. Kevin Roberson of Michael Foods have conducted a series of experiments to determine the nutritional contribution and addition rates of DDGS to layer diets. Published research indicated that DDGS could be incorporated into diets fed to laying hens at 10 percent with no deleterious effect on commercial production parameters.
Generally, previous studies have evaluated DDGS over a short period. Based on the need for standardization of product which can vary widely in composition, Dr. Scheideler elected to use a standard product of known composition so results could be applicable to commercial production.
The response of hens was evaluated using Dakota Gold DDGS over two complete cycles. Dietary treatments included a basal control, and 5 percent increments ranging from 5 to 25 percent DDGS.
The results of commercial parameters including egg production, feed intake, hen weight and internal quality variables (Haugh units and specific gravity) were unaffected by any level of DDGS inclusion. A transitory increase in feed intake occurred during the fist cycle as a result of low (65 degrees F) temperature in the test facility and feed intake was depressed during the second phase over a short period as a result of hot weather. Average egg weight was significantly (p>0.05) at the 20 to 25 percent inclusion rate.
Average yolk color increased proportionately to the DDGS content with a range on the Roche scale of 5.6 to 7.2 units. During the second phase extending from 46 to 76 weeks there were no differences or trends in egg production, egg weight, specific gravity or Haugh unit values. During the second phase, total sulfur containing amino acid level was increased from 0.71 to 0.78. This change was probably responsible for consistency in egg weight among treatments.
Based on the three-fold concentration effect from the corn supplied to the refinery, mycotoxicosis is regarded as a potential problem with DDGS. The level of seven significant mycotoxins in the DDGS used in the trial was assayed.
Based on the comprehensive study, there is no reason why DDGS should not be added to diets at levels of up to 25 percent, providing nutrient composition corresponds to the values assayed in the trial consignment. Results would of course not necessarily be applicable to DDGS samples of inferior quality or containing mycotoxins contaminants.
A parallel study of pullets was fed diets containing increments of DDGS ranging from 2.5 to 12 percent. There were no significant differences in feed intake or weight gain which were both consistent with controls which conformed to the Hy-Line W-36 standard.
The only outstanding problem relating to the use of DDGS other than consistency and quality relates to the possible contamination with virginiamycin. Lactrol, a commercial form of the antibiotic, is added to reaction vessels to suppress Lactobacilli which divert corn energy into lactic acid and decrease the yield of ethanol. Providing refineries apply lactrol below the recommended level of 25 ppm, there will be no detectable residue of virginiamycin in DDGS applying the FDA-approved microbiological assay which has a detection threshold of 0.5 to 1 ppm. of active antibiotic.
Virginiamycin is not absorbed from the intestinal tract and there is no practical risk of retention or deposition in fat or in eggs. This was demonstrated during the 1980s when no residues could be detected in the eggs of hens fed 20ppm virginiamycin over a prolonged period.
Currently, FDA has not licensed virginiamycin inclusion in layer diets although levels of up to 30 to 50 ppm are allowed for swine, broiler and turkey rations depending on species and age. Applying a strict interpretation of the FDA rule, virginiamycin may not be added knowingly to diets.
If DDGS samples do not reveal the presence of residual virginiamycin using the approved microbiological assay, the ingredient can be used in conformity with federal regulations. European regulators use an ELISA assay to screen for virginiamycin in ingredients and diets. This highly sensitive assay will detect both virginiamycin in the active form and the derived degradation products. Application of this test in the United States has demonstrated some samples with either virginiamycin or derivatives, but the levels are below the threshold of detection using the microbiological procedure which obviously only detects active virginiamycin.
DDGS has obvious financial benefits given prevailing values for corn and soybean meal and alternative energy sources. Incorporation of up to 15 percent DDGS is both practical and financially beneficial. The issues of variability and nutrient content can be overcome using a standardized ingredient subject to quality control and assay.
The present legal problem of possible virginiamycin residues should be overcome by an anticipated "no objection" ruling from the FDA. Improved production practices in refineries and the substitution of Lactrol by an alternative inhibitor of lactobacilli may also be possible solutions.