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 NH(3) emissions from the manure of growing dairy heifers with corn silage (CS) as the sole forage. Flux chamber methods were used to measure NH(3) 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 NH(3) as manure from HC heifers (314.0 vs. 174.4 +/- 36.1 microg/cm(2) per min). In experiment 2, 24 older heifers (227.9 +/- 27.1 kg of BW) were used. Manure from HC heifers released slightly less NH(3) 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 NH(3)/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, NH(3) emissions from HC heifers were not different from those from LC heifers.