Plasma vitamin C concentration was determined in healthy 48 Shiba dogs. Four dogs were younger than 1 year,12 dogs were aged between 1 and 2 years,7 dogs were aged between 2and 5 years,12 dogs were aged between 5 and 10 years, and 13 dogs were older than 10 years. Thirteen dogs were male,28 dogs were female and the other dogs were castrated female. Plasma vitamin C concentration was affected by age of dogs (P<0.001), although sex did not affect plasma vitamin C. The dogs younger than 1 year showed lower (P<0.01) plasma vitamin C concentration than the older dogs, in which plasma vitamin C was not affected by age. Plasma vitamin C concentration was 7.00±1.10 (mean±SD) mg/L and was ranged between 4.38 and 10.20 mg/L in the dogs older than 1 year. The normal level of plasma vitamin C was assumed to be between 4.8 and 9.2mg/L (mean±2×SD) in the dogs older than 1 year.

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In order to know what bacteria contribute to butyrate production in the intestinal tract of dogs, butyrate-producing bacteria were isolated from the feces. Of the 720 bacteria isolated,88 isolates produced significant amounts of butyrate (more than 10% of butyrate in the total fermentation products). Numbers of butyrate-producing bacteria, as well as the bacteria having high ability to produce butyrate, decreased with the ages of dogs, suggesting that butyrate production decreases with the age. As butyrate-producing bacteria, Eubacterium sp., Fusobacterium sp., Clostridium sp., and Butyrivibrio sp. were identified. The Butyrivibrio sp. isolated was identified as Butyrivibrio fibrisolvens. Among these butyrate-producing bacteria, the number of Eubacterium sp. was the largest. An isolate that resembled Eubacterium rectale produced a high percentage (>50%) of butyrate. Numbers of Eubacterium sp., Fusobacterium sp., and Butyrivibrio sp. also decreased with the ages of dogs, whereas the number of Clostridium sp. did not change with the age. Therefore, in senior dogs, Clostridium appears to be a predominant butyrate-producing microorganism. Since Clostridium is thought to have unfavorable effects on the host animal, it is desirable to increase the numbers of Eubacterium sp. and Butyrivibrio sp. in senior dogs, not only to increase butyrate production but also to suppress Clostridium.

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This study was conducted to examine the urine-acidifying effect and the possible adverse effects of L-cystine added to dry cat food. Six healthy adult cats, weighing 3.3 kg in average, were divided into 3 groups, and three experimental diets containing 0,2.4, and 4.8% L-cystine were allotted to the 3 groups in a 3×3 Latin square design with 8 d per period. The animals were allowed free access to the diets and water throughout the experiment, and weight gains, food intake, water intake, urine volume, daily amounts of feces were determined during the last 5 d of each period. Urine pH and the number of struvite crystals in urine were determined using fresh urine collected every morning, The remaining urine was used to determine urinary concentrations of Mg, P, urea-N, ammonia-N, creatinine and free amino acids, and the struvite activity products was given by [Mg²⁺] [NH₄⁺] [PO₄^3-]. Conversely, blood samples were take from the jugular vein on the last day of each period, and were used to determine hematocrit, and the plasma concentrations of total protein, urea-N, ammonia-N, creatinine, and free amino acids. Glomerular filtration rate was determined on the basis of creatinine concentrations in the plasma and urine. As a result, it was shown that the urine-acidifying effect of L-cystine is almost equivalent to DL-methionine (DL-Met)containing the same level of S, but is not so toxic as DL-Met. However, cystine imbalance could occur in cats, because food intake was depressed by dietary supplementation of excess L-cystine without a significant decrease in the body weight. The level of L-cystine adequate for the urine acidification in cats was considered to be less than 2.4% of dry cat food, but further studies are needed concerning this matter. Although the dietary supplementation of L-cystine did not result in an increased incidence of cystinurea or cystine urolithiasis, present results suggested a peculiarity in cats as for the urinary excretion of dibasic amino acids, especially cystine, lysine, and arginine.

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