Biofuel co-products as livestock feed - Opportunities and challenges

Hydrogen sulphide in cattle fed co-products of the ethanol industry 107Hydrogen sulphide relaxes smooth muscles from thestomach through the colon (Olson, 2011). Moreover, H 2 Sis thought to have anti-inflammatory effects in the colonbecause it enhances ulcer healing independent of nitricoxide synthase and ATP-sensitive K channel involvement(Olson, 2011). Further, in model systems, H 2 S protectsagainst and promotes healing in colitis (Olson, 2011). Incontrast, excessive sulphate entering the lower gastrointestinaltract can cause osmotic diarrhoea as the mostsignificant observable clinical finding (NRC, 2005). Thispro-inflammatory effect, in addition to cell cycle regulationeffects, explains why H 2 S can contribute to colo-rectal cancerin humans. Generally, non-ruminants respond to excessiveS by decreasing feed intake (NRC, 2005).Variability in PEM incidenceIncidence of PEM can be highly variable and is not alwaysassociated with dietary S or measurable H 2 S. Signs of PEMhave been induced in ruminants consuming diets with0.4 percent S (Gould et al., 1991), but in some studiesanimals have been fed more than 1.7 percent S withoutsigns of toxicity (Chalupa et al., 1971; Slyter et al., 1986).Ruminal H 2 S concentrations over 2000 ppm can precedethe development of PEM (Gould, Cummings and Hamar,1997). However, Drewnoski et al. (2011a) demonstratedthat steers fed high S diets (0.60 percent) consistentlyproduce H 2 S above 2000 ppm, peaking between 6 and 10hours post-feeding, without incidence of PEM. The biologicalavailability of the S source, ruminal pH and interactionswith dietary nutrients, such as divalent cations, may explainsome of the conflicting results. However, duration of feedinga high S diet, variability in S concentrations of feed,development of rumen microflora, and size of the rumenand rumen gas cap may affect responses to high S as well.Cattle consuming high S diets seem most susceptibleduring the first 15–30 days of being fed a full high concentratefinishing diet (Drewnoski, Richter and Hansen,2011). Sager, Hamar and Gould, 1990 and Low et al.(1996) both observed clinical signs of PEM beginning onday 15 after adaptation to a high-concentrate diet withexcess S. During this time, ruminal pH became increasinglymore acidic. Increased incidence of PEM early on inthe feeding period has been postulated to coincide with aspike in ruminal concentrations of H 2 S (Figure 4; McAllisteret al., 1997; Loneragan et al., 2005). After this peak, H 2 Sconcentrations decreased and no further cases of PEMdeveloped. Variability in S content of the diet, as is possiblewhen receiving multiple batches of co-products from variousplants, is also a factor in susceptibility of cattle to PEM.Spiehs, Whitney and Shurson (2002) reported a range for Scontent of DG from 12 ethanol plants of 0.33 to 0.74 percentand a within-plant coefficient of variation rangingFIGURE 4Frequency of polioencephalomalacia (PEM) in a feedlot (record analysis; McAllister et al., 1997) relative todays consuming a finishing diet overlaid with ruminal H 2 S concentrations from 9 steers fed high-sulphatewater (2360 mg/L)305 000Frequency of PEM events252015105Frequency of PEMH2S concentration4 0003 0002 0001 000Ruminal gas cap H 2S concentration (ppm)00 10 20 30 40 50 60 700Days since feedlot arrivalSource: Adapted from Loneragan et al., 2005.