Biofuel co-products as livestock feed - Opportunities and challenges

Feeding biofuel co-products to dairy cattle 137create a mild negative energy balance, all cows were fedonly grass hay for ad libitum consumption for 12 hoursbefore the experiment. This regimen was successful at elevatingplasma NEFA concentrations similar to that observedin cows during the first 2 days after calving. At 0800 thenext morning (time 0) all cows were fed 5 kg of crackedmaize. Re-feeding reduced NEFA concentrations in allcows. Treatments administered at time 0 were: (1) control,maize alone with no glycerol; (2) 1.0 kg of glycerol solution(80 percent glycerol) added to the maize; (3) 1.0 kg of glycerolsolution in 0.5 L of water and delivered as oral drenchwith a drenching bottle; and (4) 1.0 kg of glycerol in 9 Lof water and delivered into the rumen via a McGraff pumpand an esophageal tube. Blood samples were collected at-1, -0.5, 0, 0.25, 0.5, 0.75, 1, 1.5, 2, 4, 6, 8, 12 and 24hours relative to administering glycerol. Rumen sampleswere collected at 0, 2, 4 and 6 hours. After administrationof glycerol, concentrations of acetate decreased in rumensof all cows given glycerol, regardless of method of delivery.Likewise, propionate and butyrate were increased byglycerol in all forms, with peak concentrations at 4 hours.Glucose concentrations in plasma increased in cows thatwere drenched with glycerol or received tube delivery ofglycerol into the rumen compared with both the controland glycerol-fed cows. For drenching and tubing, respectively,glucose reached peak concentrations at 1.5 and3 hours. Compared with the control, glucose response,expressed as area under the curve over baseline, at 6 h wasgreater for drenching or tube delivery but not feeding glycerol.Insulin concentrations in plasma were also increasedfor drenching and tubing, reaching peak concentrations at1.4 and 1.1 hours, respectively. Finally, BHBA was increasedin plasma of all cows receiving glycerol, reaching peakconcentrations at 2.5, 2.4 and 1.6 for drenching, tubingand feeding, respectively. Conclusions from this researchare that to be glucogenic, glycerol must either be deliveredin water to associate with the liquid fraction of the rumencontent, or be able to “bypass’ the rumen in some formto be absorbed as glycerol and converted to glucose bythe liver.Glycerol is an efficient glucogenic substrate because itenters the gluco neogenesis pathway at the triose phosphatelevel and therefore is not affected by two of therate-limiting gluco neogenic enzymes. Logically, the dairycow in negative energy balance has pathways activatedfor utilization of glycerol liberated from mobilization andhydrolysis of triglycerides from body fat. This activity isdependent upon absorption of glycerol rather than fermentationto propionate and butyrate, which is somewhatcounter productive in view of the ketogenic nature ofbutyrate. If absorbed intact, glycerol is a highly efficientglucogenic substrate. Glycerol that is available to rumenmicrobes will be converted to propionic and butyric acids.The fraction converted to butyrate is metabolized to BHBAby the ruminal epithelium, thus glycerol that is fed in thediet instead of dosed is actually ketogenic rather thanglucogenic.Glycerol during lactation as an energysupplementSchröder and Südekum (1999) determined the suitabilityof glycerol as an energy source in ruminant diets. Usingwethers fed low- and high-starch concentrates, they addedglycerol at 10, 15 or 20 percent of diet DM. With a lowstarchconcentrate diet they observed no effect on digestibilityof organic matter, starch or cell-wall components.Feeding the same concentrations of glycerol in high-starchconcentrate diets resulted in a decrease in cell-wall digestibilitywith no effect on the digestion of organic matteror starch. It appears that glycerol would act similarly toa carbohydrate (as opposed to a fat) in the rumen whenformulated into typical high-forage, dairy diets. The authorsdetermined the energy density of glycerol to be 1.98 to2.27 Mcal/kg NEL.Schröder and Südekum (1999) also used four rumencannulatedsteers to evaluate the effects of feedingglycerol. Steers consumed an average of 13.3 kg/day, ofwhich 2.1 kg/day of starch for those fed control dietswas substituted with 1.09 kg/day of glycerol of differingpurities along with 1.4 kg/day of starch for steers fed thetreatment diets. Feeding glycerol did not affect diet digestibility,but decreased the acetate:propionate ratio, increasedruminal butyrate concentrations and stimulated more waterintake. These changes would be beneficial to the dairy cowbecause (1) increasing ruminal propionate would increasethe supply of this gluconeogenic substrate to the liver; and(2) increasing ruminal butyrate would support the growthof the ruminal epithelial tissue and perhaps increase nutrientabsorption from the rumen, as indicated by Dirksen,Liebich and Mayer (1985).Because of results from the DeFrain transition cowexperiment at South Dakota State University, it was decidedto test glycerol at similar feeding amounts in mid-lactationcows as an energy supplement (Linke et al., 2006). Sixprimiparous Holstein and six primiparous Brown Swiss cows(192 DIM; SD ± 150), were assigned to one of three dietsin a Latin square design with four-week periods. The dietswere: (1) a control diet containing no glycerol; (2) low glycerol,with 0.5 kg/day of glycerol; and (3) high glycerol, with1.0 kg/day of glycerol. Rumen VFA profiles showed thatmolar proportions of acetate were not changed in rumensof cows fed glycerol. Propionate tended to be increasedfor cows fed glycerol, and butyrate was increased linearlyas the amount of glycerol fed increased. DMI intakes, milkyield and 4 percent FCM were not significantly changed byglycerol supplementation. Feed efficiency, however, was