Feeding Biodiesel Co-products to Swine

Depending on its price relative to corn, crude glycerol may become a useful feed ingredient but more research is required into its safety in diets for pigs, writes Greg Simpson, swine nutritionist with Ontario Ministry of Agriculture, Food and Rural Affairs.
calendar icon 1 October 2008
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Over the last few years, the use of co-products from the ethanol industry has attracted a lot of attention and research efforts. Distillers dried grains with solubles (DDGS), condensed distillers solubles (CDS), gluten feed, distillers dried grains (DDG) are all co-products of the ethanol industry that are seeing increased use in swine rations both in prepared feeds and in on-farm mixed diets. While the food for fuel debate continues, little attention has been paid to the co-products from another driver of the "green" revolution; biodiesel.

Biodiesel can be produced from a variety of animal fats and vegetable oils. The basic process of biodiesel production is to separate the triglyceride molecules into fatty acids and the glycerol backbone. To do this triglycerides are mixed with an alcohol, usually methanol, and a chemical catalyst. Through this combination, triglycerides are broken down into methyl esters (biodiesel) and crude glycerol. For every litre of biodiesel produced, 84 grams of crude glycerol are co-generated. Crude glycerol can be further refined into glycerine and used in a variety of industrial processes including pharmaceuticals, food applications and cosmetics. However, with the rapid expansion of the biodiesel industry, the supply of crude glycerol vastly exceeds demand.

Table 1. Characterization of Crude Glycerol from Soybean Oil
Analysis Sample 1 Sample 2
Total glycerol, % 86.95 84.51
Methanol, % 0.03 0.32
pH 5.33 5.67
Moisture, % 9.63 12.23
NaCl, % 3.13 2.93
Total fatty acid, % 0.29 0.00
Crude protein, % 0.41 0.82

Samples from AGP Inc. Sergeant Bluff, Iowa

It is important to note that unlike co-products from the ethanol industry, crude glycerol is not an approved feed ingredient in Canada. The quality of crude glycerol has not been extensively studied and appears to be highly dependent on the production facility. Initial research has shown that close attention needs to be paid to both the sodium and methanol content of crude glycerol. Sodium chloride is often used as a catalyst which results in high concentrations of sodium chloride in the crude glycerol. Current biodiesel processing techniques utilize methanol which is not completely recovered and residue levels remain in the crude glycerol. Methanol is poisonous at relatively low levels. The metabolism of methanol results in the accumulation of formate, which depresses the central nervous system, and causes vomiting, severe metabolic acidosis, blindness and Parkinson-like motor disease. Further research and safety assessments will be needed to determine if there is a level of methanol residue that is acceptable for crude glycerol before it can be used in animal feed.

Limited work has been completed on using crude glycerol in pig diets. Research done by USDA-ARS in collaboration with Iowa State University and Mississippi State University have determined that for swine, the energy value of crude glycerol is less than vegetable oils or animal fats, and is approximately equal to corn. In a recent Iowa State University wean to finish study, pigs were fed corn-soybean meal diets containing 0, 5 or 10% crude glycerol. Diets were formulated so that energy level, amino acid levels, available phosphorus and sodium chloride were constant across dietary treatments. Average daily gain, average daily feed intake and feed conversion were not affected by dietary treatment. Carcass quality was not influenced by diet and a sensory evaluation of cooked loin chops found no effect of dietary treatment. Importantly, no pigs demonstrated clinical symptoms of methanol toxicity. Kidney, liver and eye tissue, the toxicological targets of methanol poisoning, were also examined. No gross lesions were found and the frequency of histological lesions was not influenced by dietary treatment.

The initial research into the use of crude glycerol is promising. From a nutritional perspective crude glycerol appears to be a good energy source and, if priced below corn, a cost effective replacement for corn in a corn-soybean meal diet. However, much more research and safety assessments will be needed before crude glycerol will be available to use in swine rations.

September 2008

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