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Effects of reduced dietary cation and anion difference on production, nutrient digestibility, and urine pH in lactating cows.

C. Lee

Events

06-22-2020

Abstract:

92
Effects of reduced dietary cation and anion difference on production, nutrient digestibility, and urine pH in lactating cows.
C. Lee*1, J. E. Copelin1, L. R. Rebelo1, P. A. Dieter1, W. P. Weiss1, T. Brown2. 1Department of Animal Sciences, Ohio Agricultural Research and Development Center, The Ohio State University Wooster, OH, 2Dairy Nutrition Plus Ralston, IA.

Manure acidification is an effective strategy to lower ammonia emissions from manure and increase its value as fertilizer. Lowering dietary cation and anion difference (DCAD) can reduce urine pH and this may acidify manure depending on the degree of pH reduction in dairy cows. However, reducing DCAD can negatively affect DMI, production and fiber digestibility. The objective was to examine lactating cows fed a diet with reduced DCAD on production, fiber digestibility, and urine pH. Twenty cows were used in a randomized block design and fed 1 of the following 3 diets: a diet with DCAD of 220, 150, or 75 mEq/kg (n = 6, 7, and 7, respectively; DCAD, Na + K − Cl − S; 16.8% CP, 33% NDF on DM basis). SoyChlor replacing soybean meal and corn grain was used to decrease DCAD. The experiment was conducted for 5 wk to monitor DMI and production and spot fecal samples were collected in wk 5 to estimate fecal output and apparent total-tract nutrient digestibility. In wk 5, urine samples were also collected (every 4 h in a 24-h cycle) to estimate urine volume (creatinine) and measure urine pH. Data were analyzed using the MIXED procedure of SAS (block as random and diet as fixed effect). Reducing DCAD lowered (25.3 to 23.6 kg/d; P = 0.02) DMI in a linear manner. Milk yield, ECM, and ECM/DMI were not different (P > 0.26) among treatments. Milk component contents and yields were not affected by level of DCAD. Total-tract apparent digestibility of DM and NDF did not differ among treatments. Estimated urine volume increased (36 to 44 kg/d; P < 0.01) and urine pH decreased (8.25 to 7.86; P < 0.01) in a linear manner with decreasing DCAD. In conclusion, lowering DCAD of a lactation diet from 220 to 75 mEq/kg decreased DMI and numerically decreased milk yield (38.4 to 36.9 kg/d). However, the decreases in DCAD did not affect DM and NDF total-tract digestibility. Although an increase in urine volume and decrease in urine pH with decreasing DCAD was observed, we do not know whether these changes are effective in lowering ammonia emission from manure.

Keywords: dietary cation and anion difference, digestibility, and urine pH.