Effects Of Dietary Cation Anion Difference On Performance Acid Base Status And Nitrogen And Macromineral Metabolism Of Lactating Dairy Cows

Author : Haley M. Zynda
Publisher :
ISBN 13 :
Total Pages : 82 pages
Book Rating : 4.:/5 (131 download)

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Download or read book Exploring the Effects of Lowered Dietary Cation-anon Difference on Lactation Performance and Reduction of Manure Ammonia Emissions in Lactating Cows written by Haley M. Zynda and published by . This book was released on 2021 with total page 82 pages. Available in PDF, EPUB and Kindle. Book excerpt: Livestock and poultry production are the leading contributors to NH3 emissions in the United States. While NH3 is not itself a greenhouse gas (GHG), it forms nitrous oxide and small particulate matter (PM2.5, i.e, smog) that is of concern for environmental agencies and poses human health risks. Nitrogen also can leach into soil and potentially cause eutrophication of water sources. For livestock producers, N loss from manure is costly, both from the perspective that it is going unused by the animal and that the manure will not serve as useful a fertilizer for crop production. Acidifying dairy manure with addition of strong acids, such as HCl or H2SO4, is the most widely studied method of reducing NH3 emissions but increases the cost for manure management. Reducing the dietary cation-anion difference (DCAD; Na + K -Cl - S) is a strategy typically used to reduce hypocalcemia after parturition, but we hypothesized that DCAD can be a potential strategy to lessen the environmental impact of the dairy industry when applied to lactating cows. Urine pH can be reduced with the inclusion of anionic salts in cow rations, thus perhaps influencing the overall pH of the manure slurry. Two experiments were designed to evaluate the effectiveness of feeding a diet with reduced DCAD to lactating cows to mitigate manure NH3 emissions while still maintaining milk production and nutrient digestibility. In the first experiment, 27 cows were randomly assigned to 1 of 3 diets with differing DCAD (193, 101, and 1 mEq/kg DM). The DCAD did not affect milk yield but tended to decrease milk fat yield without affecting milk fat content as DCAD decreased. Milk protein yield was not different among treatments. In addition, nutrient digestibility (i.e., DM, OM, NDF) did not differ among treatments. The low DCAD diet successfully reduced pH of urine and manure, but manure incubation did not result in statistical differences in NH3 emissions among treatments. Ammonia emission was probably not reduced because of the high fecal to urine ratio and slight increases in urine pH during freezing and thawing between urine collection and manure incubation. Therefore, the second study sought to determine the necessary decreases in urine pH needed to decrease manure pH low enough to reduce NH3 emissions from manure. Feces and urine were collected from 4 lactating cows, composited, and brought back to the laboratory. The urine was separated into 4 subsamples, and pH was reduced to 8.5, 7.5, 6.5, and 5.5 using concentrated H2SO4. Manure was reconstituted, using the feces and urine subsamples, in a fecal to urine ratio of 2:1, which was the ratio often seen in previous studies for high producing Holstein cows. The manure was then incubated for 5 days. Results indicated that a urine pH of 7.5, 6.5 and 5.5 linearly reduced NH3 volatilization when the fecal to urine ratio was 2:1. Overall, reducing DCAD can be a potential strategy of mitigating NH3 emission from manure, but potential loss of milk fat should be considered. Additionally, feces to urine ratios can be a critical factor for successful mitigation of NH3 from manure by feeding a reduced DCAD diet. Further research is needed to determine optimal level of reduced DCAD that can mitigate ammonia emissions from manure without negatively affecting production.