A series of five experiments were conducted to develop instrumentation to measure ammonia volatilization from manure in naturally ventilated dairy barns as well as under controlled, laboratory conditions. In addition, these procedures were used to evaluate precision feeding strategies on ammonia volatilization, while nitrogen utilization, and milk production and components were evaluated in Holstein dairy cows. Lastly, the impact of the level of zeolite inclusion mixed into a totally mixed ration on nitrogen utilization and nutrient digestibility was evaluated in continuous culture fermenters.
Experiment I involved using a non-steady state flux chamber coupled to a photoacoustic gas monitor to measure ammonia emissions directly from a freestall dairy barn floor. The barn housed two groups of 60 animals fed either alfalfa or grass silage based rations and alternated between a fine ground or a coarse ground corn through four periods in a switchback design. Dry matter intake (DMI) milk production and components and nitrogen utilization efficiency of each group of animals were evaluated. Nitrogen utilization efficiency was not significantly different between rations, regardless of forage source or corn particle size and averaged 37.4%. Ammonia emissions from manure were not significantly different between treatment groups and averaged 3 kg/d, equivalent to 0.05 kg/cow/d.
Experiment II involved the development of a laboratory, steady-state flux chamber coupled to a photoacoustic gas monitor, to measure ammonia volatilization from manure. Five urine to feces ratios (10:90, 30:70, 50:50, 70:30 and 90:10) were used to evaluate the instrumentation, and determine ammonia volatilization. The gas monitor demonstrated that in scenarios where urease was limiting (90:10, 70:30) ammonia production was gradual compared to instances in which urea was limiting (10:90, 30:70) where rates of ammonia production were much faster.
Experiment III involved a using a replicated 4 x 4 Latin square to evaluate the effects of forage source and corn particle size on animal performance and ammonia (NH3) volatilization from manure. The same four rations, as fed in experiment I were evaluated. Cows fed alfalfa silage had a greater dry matter intake (DMI) compared to cows fed grass silage based rations (27.9 vs. 22.1 kg/d, respectively). The increased DMI for cows fed alfalfa silage resulted in greater milk yield (35.3 vs. 30 kg/d; P < 0.01)) than for cows fed grass silage based rations. Corn particle size had no effect on DMI, milk yield, FCM or milk yield efficiency. Milk fat, protein and milk protein percentages were higher for cows fed alfalfa based rations vs. grass based rations diets. Regardless of forage source or corn particle size, all rations resulted in similar cumulative amounts of ammonia being volatilized from manure, although the fine ground corn resulted in a numerically lower release of ammonia from manure.
Experiment IV involved using a replicated 4 x 4 Latin square to evaluate the effects of forage preservation method (silage vs. hay) and corn particle size on animal performance, N excretion and ammonia emissions. Fine ground corn resulted in a significant increase in ammonium-N content of manure when fed with the silage based ration, but decreased the ammonium-N content of manure when fed with hay based rations compared to coarsely ground corn. Corn particle size had no significant impact on urinary urea concentrations (UUN). Urine from cows consuming silage based rations had significantly lower urea concentrations (667.9 mg/dL) compared to urine from animals consuming hay based rations (773.0 mg/dL). This difference in UUN of approximately 100 mg/dL between the silage and hay based rations, did not result in considerable differences in ammonia volatilization when urinary urea nitrogen was used as an input parameter in an ammonia volatilization simulation model.
Experiment V involved using a dual-effluent continuous culture system to evaluate the effects of level of zeolite in a total mixed ration on ruminal fermentation. A Latin square design was used to evaluate 0 (control), 0.6, 1.2 and 1.8% zeolite addition to a basal ration on ruminal fermentation. Zeolite addition to the diet had no effect on buffering capacity of the rumen environment. The addition of zeolite to the ration resulted in changes in pH, propionate concentrations and bacterial N, primarily due to the 1.2% zeolite addition. Including zeolites in dairy rations alters ruminal fermentation, especially pH and ammonia concentrations. However, responses to zeolite addition is influenced by the level of inclusion in the ration, and under the conditions of this study, 1.2% zeolite inclusion resulted in reduced ammonia concentrations, without negatively impacting nutrient digestibility or microbial crude protein synthesis. (Abstract shortened by UMI.)
