Fecal ammonia, urea, volatile fatty acid and lactate levels in dairy cows and their pathophysiological significance during diarrhea
ABSTRACT Normal fecal samples were taken from lactating cows fed either a total mixed ration (TMR; n = 30) or pasture-based diet (20) and from dry cows fed mainly on hay (15). Diarrheic fecal samples (n = 51) were collected from 21 sick dairy cows. Fecal analyses of ammonia, urea, lactate and volatile fatty acid (VFA) levels were used to evaluate colonic fermentation. Most normal feces had reasonably neutral pH, however, alkaline feces were observed in diarrheic cows. Although fecal lactate is higher in cows on grazing pasture, lactate levels were generally lower in the cows in the present study. Fecal VFA levels were higher in lactating cows than in dry cows. Elevated fecal urea was observed in diarrheic cows, however, many fecal samples in normal and diarrheic cows contained no urea. Fecal VFA levels in diarrheic cows were lower than in normal lactating cows, but were approximately equivalent to those in dry cows. Grazing or dry cows showed higher acetate and lower n-butyrate proportions compared with TMR-fed or diarrheic cows. Higher proportions of branched chain VFAs were observed in diarrheic cows, and the lowest level was observed in grazing cows. The present results indicate that intracolonic nitrogen equilibrium and proteolytic fermentation are altered by diarrheic status.
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- "Rumen data: Abrahamse et al. (2008a, 2008b, 2009), Cameron et al. (1991), De Visser (1993), Kalscheur et al. (1997), Kennelly et al. (1999), Robinson et al. (1997), Stensig and Robinson (1997), Sutton et al. (1986), Taweel et al. (2005), Van Vuuren (1993), Yang et al. (2001). Fresh fecal data: Bach et al. (2005), Gressley and Armentano (2005), Sato and Nakajma (2005), Siciliano-Jones and Murphy (1989), Sindt et al. (2002), Sindt et al. (2004). differences in ruminal fermentability of the non-fiber substrate. "
ABSTRACT: Volatile fatty acids (VFA) and lactic acid can build up in the rumen and reduce ruminal pH. Low ruminal pH for prolonged periods each day can affect feed intake, microbial metabolism and feed digestion, and has also been related to inflammation, diarrhea and milk fat depression. This paper considers aspects of pH regulation, as well as the effects of ruminal pH on rate of substrate degradation and on the profile of VFA available for absorption. Removal of VFA from the rumen by passage in the liquid phase and by absorption through the rumen wall are major processes that influence ruminal pH. The buffering capacity (BC) of rumen fluid is variable and is generally assumed to depend primarily on bicarbonate. Bicarbonate-dependent absorption is not just a primary absorption pathway of VFA but can also secrete bicarbonate at a capacity equal to that from saliva, thus removing protons from the rumen by neutralization. In addition, the inherent BC of the diet is involved in pH regulation, largely explained by the cation exchange capacity of feedstuffs. Empirical models to predict ruminal pH have had limited success. The inclusion of dietary characteristics in those models is needed to improve prediction accuracy. Representations of the effect of pH on fiber degradation adopted in models of ruminal function differ widely and include linear decline, saturation-type and sigmoidal relationships. In comparison with pH effects on degradation of fiber in sacco, most representations tend to overestimate the inhibiting effect of pH. Because the products of fiber hydrolysis are a major source of energy for microbial growth in the rumen, proper understanding and representation of fiber degradation at low pH is vital to predict microbial protein supply and VFA production satisfactorily. Variation in VFA profile is associated with variation in methane production, nutrient partitioning and milk composition. Various ruminal bacterial species have been observed to shift pathways in response to changes in pH while fermenting the same substrate. Mechanistic rumen models have adopted VFA stoichiometric coefficients related to type of substrate present in the feed or fermented in the rumen, but the majority of models do not include the effect of pH on VFA profile. In conclusion, ruminal pH is a major determinant of the profile of nutrients available for absorption. Shifting focus to factors other than salivary bicarbonate secretion will aid in better understanding ruminal pH regulation. Improved models to predict effects of ruminal pH on microbial metabolism and VFA profile will enable further optimization of dairy cow nutritionAnimal Feed Science and Technology 02/2012; 172(1-2):22-33. DOI:10.1016/j.anifeedsci.2011.12.005 · 2.09 Impact Factor
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ABSTRACT: To clarify the significance of fecal organic anions in neonatal diarrhea, a total of 252 fecal samples (91 diarrheic, 161 normal) were collected from 136 dairy calves (including three crossbreds) less than 4 weeks old. Fecal pH, D- and L-lactate, succinate and volatile fatty acid (VFA) were analyzed. In normal feces, lactate was highest and VFA was lowest at week 1 of age, and lactate progressively decreased and VFA progressively increased with advancing age. In diarrheic samples, although higher pH and lower lactate levels were confirmed at week 1, samples at weeks 3–4 showed lower pH and VFA accompanied by higher lactate of D and L-isomers. In diarrhea, fecal butyrate was significantly lower at all stages, but succinate levels did not differ significantly. The proportion of lactate to organic anions (sum of lactate, succinate and VFA) in diarrheic feces was lower at week 1, and higher in weeks 2–4, while that of VFA to organic anions showed the opposite pattern. Strong relationships were observed between fecal pH and lactate, and VFA proportions in organic anions, though the relationship was weak in diarrhea. Most of the elevated lactate was observed in fecal samples with lower VFA. However, succinate had no relationship with VFA or lactate levels.Animal Science Journal 03/2008; 79(2):187 - 192. DOI:10.1111/j.1740-0929.2008.00516.x · 1.04 Impact Factor
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ABSTRACT: Using 24 diarrheic dairy calves under 8 weeks old, multiple fecal samples (4-12) were collected individually during the clinical advancing (max. 10 days) to evaluate the importance of fecal ammonia, lactate and volatile fatty acid (VFA) levels. Removing 3 calves not recovered during the sampling, 21 calves were grouped into under 3 weeks (< 3 wk; n=11) and 3-8 weeks old (3-8 wk; n=10). Data were divided into diarrheic and recovered feces with averaging in individuals. Diarrheic feces showed lower VFA and n-butyrate, and higher acetate proportions than recovered feces at <3 wk, but not at 3-8 wk. Diarrhea showed higher lactate, and lower ammonia and minor VFA (i-butyrate, valerate), which might reflect insufficiency in gut flora and fermentation.Journal of Veterinary Medical Science 01/2009; 71(1):117-9. DOI:10.1292/jvms.71.117 · 0.88 Impact Factor