Biofuel co-products as livestock feed - Opportunities and challenges

Utilization of crude glycerin in beef cattle 15745FIGURE 2Growth and anticipated world expansion of biodiesel production4035302520World BiodieselProduction, billion litres15105020002002200420062008201020122014201620182020Source: National Biodiesel Board, 2008.Pellet Durability Index, %FIGURE 3Effects of crude glycerin on pellet durability indexof swine feeds97959391Molar ProportionFIGURE 4Molar proportions of acetate and propionate afterfermentation of glycerin by mixed cultures ofruminal bacteria from grain-fed cattle100755025890 3 6 9 12 15Glycerol, %0AcetateStarchPropionateGlycerolin the scientific literature. Lee et al. (2011) reporteddecreases in the acetate-to-propionate (A:P) ratio as glycerolreplaced alfalfa or maize silage in in vitro cultures of mixedruminal microorganisms. We have noted similar effects inour laboratory for in vitro incubations in which maize starchwas replaced by increasing proportions of pure glycerol(Figure 5; unpublished data). The A:P ratio decreasedlinearly as level of glycerin in the mixtures increased.Bergner et al. (1995) measured glycerin transformation byruminal microorganisms using 14 C-labeled glycerin, andobserved that the majority of glycerin was converted topropionate, while no discernible amounts were convertedto acetate. Similarly, Trabue et al. (2007) found thatglycerol partially suppressed acetate production by ruminalmicrobes in inoculum taken from a dairy animal fed adiet consisting of approximately 50 percent concentrate.In contrast, Wright (1969) determined that radio-labelledglycerin was converted to acetate, propionate and butyrate.The inoculum used in their study was extracted fromcattle grazing clover-ryegrass pastures. Jarvis, Moore andThiele (1997) utilized ruminal contents from red deer, anddetermined that a Klebsiella planticola strain transformedglycerin into approximately equimolar proportions offormate and ethanol. Collectively, these studies maysuggest that metabolites of glycerin are influenced by themicrobial milieu within the rumen, which obviously is afunction of diet.Digestion of fibre is of particular relevance in diets supplementedwith glycerin. Roger et al. (1992) reported thatcellulolytic activity was depressed by glycerol, noting that it