Effect of forage-to-concentrate ratio in dairy cow diets on emission of methane, carbon dioxide, and ammonia, lactation performance, and manure excretion
2011
Aguerre, M.J. | Wattiaux, M.A. | Powell, J.M. | Broderick, G.A. | Arndt, C.
Holstein cows housed in a modified tie-stall barn were used to determine the effect of feeding diets with different forage-to-concentrate ratios (F:C) on performance and emission of CH₄, CO₂ and manure NH₃-N. Eight multiparous cows (means ± standard deviation): 620±68kg of body weight; 52±34 d in milk and 8 primiparous cows (546±38kg of body weight; 93±39 d in milk) were randomly assigned to 1 of 4 air-flow controlled chambers, constructed to fit 4 cows each. Chambers were assigned to dietary treatment sequences in a single 4×4 Latin square design. Dietary treatments, fed as 16.2% crude protein total mixed rations included the following F:C ratio: 47:53, 54:46, 61:39, and 68:32 [diet dry matter (DM) basis]. Forage consisted of alfalfa silage and corn silage in a 1:1 ratio. Cow performance and emission data were measured on the last 7 d and the last 4 d, respectively of each 21-d period. Air samples entering and exiting each chamber were analyzed with a photo-acoustic field gas monitor. In a companion study, fermentation pattern was studied in 8 rumen-cannulated cows. Increasing F:C ratio in the diet had no effect on DM intake (21.1±1.5kg/d), energy-corrected milk (ECM, 37.4±2.2kg/d), ECM/DM intake (1.81±0.18), yield of milk fat, and manure excretion and composition; however, it increased milk fat content linearly by 7% and decreased linearly true protein, lactose, and solids-not-fat content (by 4, 1, and 2%, respectively) and yield (by 10, 6, and 6%, respectively), and milk N-to-N intake ratio. On average 93% of the N consumed by the cows in the chambers was accounted for as milk N, manure N, or emitted NH₃-N. Increasing the F:C ratio also increased ruminal pH linearly and affected concentrations of butyrate and isovalerate quadratically. Increasing the F:C ratio from 47:53 to 68:32 increased CH₄ emission from 538 to 648g/cow per day, but had no effect on manure NH₃-N emission (14.1±3.9g/cow per day) and CO₂ emission (18,325±2,241g/cow per day). In this trial, CH₄ emission remained constant per unit of neutral detergent fiber intake (1g of CH₄ was emitted for every 10.3g of neutral detergent fiber consumed by the cow), but increased from 14.4 to 18.0g/kg of ECM when the percentage of forage in the diet increased from 47 to 68%. Although the pattern of emission within a day was distinct for each gas, emissions were higher between morning feeding (0930h) and afternoon milking (1600h) than later in the day. Altering the level of forage within a practical range and rebalancing dietary crude protein with common feeds of the Midwest of the United States had no effects on manure NH₃-N emission but altered CH₄ emission.
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