Glycerin in Swine Diets

SUMMARY

Crude glycerin is a by-product of the biodiesel production, which has been shown to be a good energy source for swine. There is variability in the energy available from crude glycerin, which is partially explained by the glycerin content of the crude glycerin. Up to 15% crude glycerin has been fed to pigs without negative consequences. Methanol, which is potentially toxic to swine, will be present in varying concentrations in crude glycerol. Because crude glycerin is a liquid it can cause problems with feed manufacturing and feed flowability but has been shown to improve pelleting. When diets are formulated with crude glycerin the grain (energy source) will decrease but the soybean meal or other protein source will increase if a ME:amino acid ratio is maintained.

WHAT IS GLYCERIN?

Also, commonly called glycerol, glycerin is traditionally used in making of soaps, cosmetics, and lotions. It has a sweet taste and can be used as a sweetener in foods or animal feeds. When fats and oils are made into biodiesel, crude glycerin is a by-product; 79 g of crude glycerin is produced per litre of biodiesel (Thompson and He, 2006). In the body it is a backbone of tri-phospholipids and can be broken down in the liver and converted to glucose to be used by the body as an energy source. Energy cost is sixty percent of the total cost of swine diets. Therefore, because of the increase in biodiesel production there has been increased interest in using glycerin as an energy source in animal feeds.

To use glycerin as energy source it is important to determine the amount of energy available to the pig. However, there can be tremendous variability between sources of glycerin. Kerr et al. (2009) evaluated the digestible and metabolizable energy values from several sources of crude glycerin for nursery pigs and reported a range of gross energy (GE) from 3,173 to 6,021 kcal/kg; of digestible energy (DE) of 3,022 to 5,228 kcal/kg; and of metabolizable energy (ME) from 2,535 to 5,206 kcal/kg. Kerr et al. (2009) used regression analysis to estimate gross energy of glycerin based on composition with good results, where GE kcal/kg = -236 + (46.08 x % of glycerin) + (61.78 x % of methanol) + (103.62 x % of fatty acids), (R2 = 0.99); he also suggested that ME could be estimated at 85.4% of GE. Lammers et al. (2008b) used linear regression to determine a DE value of 3,344 kcal/kg and an ME of 3,207 kcal/kg when a crude glycerol source (86.95% glycerol) was fed to growing pigs. And suggested an equation to calculate the ME of crude glycerin as follows: ME of crude glycerin = GE of pure glycerin (4,305 kcal/kg) x purity of crude glycerin. 

Table 1. Glycerin and Pig Performance

Mendoza et al. (2010) determined that the ME of purified glycerol (30% addition) added to diets for finishing pigs was 3,584 kcal/kg of dry matter, this value would be similar to that of corn.

Zijlstra et al. (2009) showed increased body weight when 4 or 8% glycerol replaced wheat (with the appropriate additions of crystalline amino acids) in diets for nursery pigs. Feed intake also tended to increase, which resulted in no change in feed efficiency during the twenty-one day experiment. In similar results, ADG improved linearly in nursery pigs when fed 3 or 6% glycerin replacing corn (Groesbeck et al., 2010).

Lammers et al. (2008a) added 5 or 10% glycerin to diets for pigs starting one week after weaning (BW = 7.9 kg) and continuing through the finishing period. The addition of glycerin did not have any affect on animal performance in any stage or overall. There were no effects on carcass characteristics except for the fatty acid profile. Diets in this experiment did not simply replace corn or wheat with glycerin but were formulated to have the same ME, lysine, sulphur amino acids, threonine, tryptophan, available phosphorus, sodium and chlorine content as the control diets. The equation suggested by Lammers et al. (2008b) was used to calculate ME of the glycerin used in the study. The glycerin used had analyzed values for Na and Cl of 1.20 and 1.71, respectively. When 5% glycerol was added to the diet it replaced 6% of the corn and 50% of the NaCl while soybean meal increased by 5%. In the diets with 10% added crude glycerol 16% corn and 90% NaCl were replaced and soybean meal increased by approximately 9% (Kerr et al., 2008). 

Two other experiments have been were reported using the Lammers´sequation to calculate ME; Mendoza et al. (2010) and Schieck et al. (2010). Mendoza, et al. (2010) fed up to 15% refined glycerin with no effect on growth performance, carcass or pork quality measurements when diets were formulated to the same ME. However, Schieck et al. (2010) saw increased ADG and ADFI and decreased G:F when 8% crude glycerin was fed for 12 weeks in the grow-finish period. Adding glycerin in this experiment improved belly firmness but had no other effect on carcass quality, water-holding capacity, or taste.

Crude Glycerin is not currently listed in Schedule IV for swine in Canada. It is, however, listed in Schedule IV for use in beef cattle feeds up to 5% of the total diet.

Crude glycerin (or crude glycerol or crude 1,2,3-propanetriol) is 1,2,3-propanetriol derived as a by-product of the biodiesel fuel manufacturing process. It shall not contain greater than 0.1% residual methanol.

It shall be labelled with the following statement: "This product is for use as an energy source in beef cattle feeds at a level not to exceed 5.0% of the total diet. / Ce produit est utilisé comme source d´énergie dans les aliments destinés aux bovins de boucherie, en quantité ne devant pas dépasser 5 pourcent de la ration totale."

It shall be labelled with guarantees for minimum percent glycerol, maximum percent moisture and maximum percent methanol.

Methanol is used in during the biodiesel manufacturing process and some methanol will remain in the crude glycerin by-product. Methanol can be toxic to animals at low levels. The CFIA has said that when glycerin is used in beef cattle diets it can not contain greater than 0.1% (1000 ppm) methanol.

Sodium and chloride can be found in crude glycerin in relatively high concentrations. It may be advantageous to adjust the amount of salt in the diet to account based on the amount of Na and Cl in the glycerin. Adding glycerin to the diet has been shown to increase water intake and urinary output.

Form

Glycerin is typically a liquid at room temperature. This means that it needs to be stored in a tank at the feed mill and added as a liquid. Adding more than 6% glycerin to a mash diet can result in feed with flowability problems. However, Groesbeck et al. (2008) showed that adding up to 9% glycerin increased pellet durability and decreased friction at the pellet mill, improving production efficiency.

CONCLUSIONS

While not currently approved for use in swine in Canada crude glycerin is a good energy source for swine. There is variability in the energy available from crude glycerin, but the energy content can be estimated by the composition. Methanol is an impurity found in crude glycerin, which is potentially toxic. Because crude glycerin is a liquid it can cause problems with feed manufacturing and feed flowability but can improve the pelleting process and pellet quality. When diets are formulated with crude glycerin they will have a lower energy source and a higher protein source, salt may also need to be decreased.

Groesbeck, C.N. L.J. McKenney, J. M. DeRouchey, M.D. Tokach, R.D. Goodband, S.S. Dritz, J.L. Nelssen, A.W.Duttlinger, A.C.FAhrenholz, and K.C. Behnke. 2008. Effect of crude glycerol on pellet mill production and nursery pig growth performance. J. Anim. Sci. 86:2228-2236. 

Kerr, B.J., T.E. Weber, W.A. Dozier, III and M.T. Kidd. 2009. J. Anim. Sci. Digestible and metabolizable energy content of crude glycerin originating from different sources in nursery pigs. J. Anim. Sci. 87:4042-4049.

Kerr, B.J., M. Honeyman, P. Lammers, S. Hoyer. 2008. Feeding bioenergy coproducts to swine. http://www.thepigsite.com/articles/2/ai-geneticsreproduction/2136/feeding-bioenergy-coproducts-to-swine Accessed December 16, 2010.

Lammers, P.J., B.J. Kerr, T.E. Weber, K. Bregendahl, S. M. Lonergan, K.J. Prusa, D. U. Ahn, W.C. Stoffregen, W.A. Dozier, III and M.S. Honeyman. 2008a. Growth performance, Carcass Characteristics, meat quality, and tissue histology of growing pigs fed crude glycerin-supplemented diets. J. Anim. Sci. 86:2962-2970.

Lammers, P.J., B.J. Kerr, T. E. Weber, W.A. Dozier, III, M.T. Kidd, K.Bregendahl, and M.S. Honeyman. Digestible and metabolizable energy of crude glycerol for growing pigs. J Anim. Sci. 2008b. 86:602-608.

Mendoza, O.F., M. Ellis, F.K. McKeith, and A.M. Gaines. 2010. Metabolizable energy content of refined glycerin and its effects on growth performance and carcass and pork quality characteristics of finishing pigs. J. Anim. Sci. 88:3887-3895.

Schieck, S.J., G.C. Shurson, B.J. Kerr, and L.J. Johnston. 2010. Evaluation of glycerol, a biodiesel co-product, in grow-finish pig diets to support and growth and pork quality. J. Anim. Sci. 88: 3927-3935.

Thompson, J.C., and B.B. He. 2006. Characterization of crude glycerol from biodiesel production from multiple feedstocks. Appl. Eng. Agric. 22:261-265.

Zijlstra, R.T., K. Menjivar, E. Lawrence, and E. Beltranena. 2009. The effect of feeding crude glycerol on growth performance and nutrient digestibility in weaned pigs. Can. J. Anim. Sci. 89:85-89.