Effects of forage-to-concentrate ratio and dietary fiber manipulation on gas emissions and olfactometry from manure of Holstein heifers

The objective of this experiment was to determine the effects of differing ratios of forage to concentrate (F:C) and fiber levels on odor and gas emissions from manure. Eight Holstein dairy heifers (362.45±4.53 d of age and 335.6±7.41kg of body weight) were randomly assigned to a split-plot, 4×4 Latin square design (21-d periods) with F:C as the whole plot (20 or 80% forage) and fiber level as sub-plot (0, 20, 40, or 60% inclusion of corn stover). Gas concentration was determined using an infrared photoacoustic analyzer over a 24-h period using a steady-state flux chamber setup. Odorous air samples were collected from chamber headspace and evaluated by 6h uman assessors using a forced-choice dynamic olfactometry technique. Emissions of CO₂ were greater for the low than high concentrate diets, and no differences were observed for NH₃ and CH₄ emissions between F:C. Although F:C had no effect on NH₃ emissions, as dietary fiber increased, a linear interaction with opposite effects was found for high and low concentrate diets. Nitrous oxide emissions were below minimum detectable levels. Neither F:C nor neutral detergent fiber level affected odor intensity. Odor emissions were successfully assessed, and manipulation of dietary fiber has the potential to influence CH₄ and NH₃ emissions.