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Effects of dietary fat source and monensin on methane to carbon dioxide ratio, VFA profile, and performance of finishing steers
A finishing study was conducted to evaluate effects of supplemental fat type and presence or absence of monensin on methane to carbon dioxide ratio (CH4:CO2), ruminal VFA profile, and performance of finishing steers. Steers (n = 60, initial BW = 414 ± 16 kg) were individually fed for 125 d using Calan gates. Steers were stratified by initial BW and assigned randomly to one of six treatments. Four diets were designed to compare fat source: CON (corn-based diet with no added fat), MDGS (50% modified distillers grains plus solubles added), OIL (3% corn oil added), and TAL (3% tallow added). Added fat diets were formulated to provide 6.5% total dietary fat. An additional two treatments were added to factorialize presence or absence of monensin (375 mg daily) with CON or MDGS diets. At time of feeding, exhaled breath samples were collected from each animal at weekly intervals throughout the study using a custom built automated gas collection system and were analyzed for CH4 and CO2, using gas chromatography. Carbon dioxide was used as an internal marker and CH4:CO2was used to quantify the effects of diet on methane emission. Rumen fluid collected via esophageal tubing on d 55, prior to feeding, was analyzed for VFA profile. Treatment differences were evaluated using pre-planned contrasts. No diet × monensin interaction was observed (P = 0.19). The CH4:CO2 for cattle fed MDGS was greater (P = 0.03) than CON, 0.057 compared to 0.050, respectively. No effect (P = 0.56) of monensin inclusion on CH4:CO2 was observed. Differences in CH4:CO2 observed may be due to composition of dietary fat, as steers fed MDGS had greater CH4:CO2 than those fed TAL or CON (P < 0.03), while those consuming OIL were intermediate. No differences were observed (P = 0.45) for ruminal acetate to propionate ratio (A:P) due to fat type or presence of monensin, as A:P of all diets fell between 1.08 and 1.40. Finishing performance was also unaffected as no differences in DMI (P = 0.48), ADG (P = 0.37), or G:F (P = 0.78) were observed. Composition of the finishing diet, particularly source of added fat does impact CH4:CO2.
Keywords: : distillers grains, fat, methane