Short Communication: Effect of Changing the Ratio of Forage to Concentrate on Ammonia Emissions by Dairy Heifers

Two animal growth studies and a companion digestibility study were conducted to evaluate the effect of differing ratios of forage to concentrate and the addition of yeast culture (Saccharomyces cerevisiae) on NH₃ emissions from the manure of growing dairy heifers with corn silage (CS) as the sole forage. Flux chamber methods were used to measure NH₃ volatilization from the barn floor or by laboratory procedures. In experiment 1, 24 Holstein heifers (159 ± 3.3 kg of initial body weight; BW) were fed either a low-concentrate diet (LC; 77% CS, 23% concentrate) or a high-concentrate diet (HC; 33% CS, 67% concentrate) in a randomized design. Manure (feces and urine mixture) from heifers consuming the LC diets volatilized similar amounts of NH₃ as manure from HC heifers (314.0 vs. 174.4 ± 36.1 μg/cm² per min). In experiment 2, 24 older heifers (227.9 ± 27.1 kg of BW) were used. Manure from HC heifers released slightly less NH₃ from the barn floor, confirming the results from the initial study. Finally, a digestibility study was undertaken using four 9-mo-old heifers (234 ± 15 kg of initial BW) and four 14-mo-old heifers (409 ± 20 kg of initial BW), allocated to 4 treatments consisting of an HC or LC diet with or without yeast culture addition. Emissions per unit of manure (mg of NH₃/g) from heifers in both age groups were greater for the HC diets; however, total emissions per day were equal. Yeast culture addition had no effect on cumulative daily emissions. In these 3 experiments, NH₃ emissions from HC heifers were not different from those from LC heifers.