The effect of dietary hydroxyproline and dietary oxalate on urinary oxalate excretion in cats1

Abstract

In humans and rodents, dietary hydroxyproline (hyp) and oxalate intake affect urinary oxalate (Uox) excretion. Whether Uox excretion occurs in cats was tested by feeding diets containing low oxalate (13 mg/100 g DM) with high (Hhyp-Lox), moderate (Mhyp-Lox), and low hyp (Lhyp-Lox) concentrations (3.8, 2.0, and 0.2 g/100 g DM, respectively) and low hyp with high oxalate (93 mg/100 g DM; Lhyp-Hox) to 8 adult female cats in a 48-d study using a Latin square design. Cats were randomly allocated to one of the four 12-d treatment periods and fed according to individual energy needs. Feces and urine were collected quantitatively using modified litter boxes during the final 5 d of each period. Feces were analyzed for oxalate and Ca, and urine was analyzed for specific density, pH, oxalate, Ca, P, Mg, Na, K, ammonia, citrate, urate, sulfate, and creatinine. Increasing hyp intake (0.2, 2.0, and 3.8 g/100 g DM) resulted in increased Uox excretion (Lhyp-Lox vs. Mhyp-Lox vs. Hhyp-Lox; P < 0.05), and the linear dose-response equation was Uox (mg/d) = 5.62 + 2.10 × g hyp intake/d (r(2) = 0.56; P < 0.001). Increasing oxalate intake from 13 to 93 mg/100 g DM did not affect Uox excretion but resulted in an increase in fecal oxalate output (P < 0.001) and positive oxalate balance (32.20 ± 2.06 mg/d). The results indicate that the intestinal absorption of the supplemental oxalate, and thereby its contribution to Uox, was low (5.90% ± 5.24%). Relevant increases in endogenous Uox excretion were achieved by increasing dietary hyp intake. The hyp-containing protein sources should be minimized in Ca oxalate urolith preventative diets until their effect on Uox excretion is tested. The oxalate content (up to 93 mg/100 g DM) in a diet with moderate Ca content does not contribute to Uox content.

Influence of protein concentration and quality in a canned diet on urine composition, apparent nutrient digestibility and energy supply in adult cats

“…Moreover, feeding a diet with a high protein level, but low protein quality decreased the renal Ca excretion in cats when data were compared with a high protein level-high protein quality group, while the renal Ox excretion was similar between these two groups [ 26 ]. This observation contrasts with findings from Dijcker et al [ 4 ], where the renal Ox excretion was increased when synthetic hydroxproline, an amino acid found in higher amounts in collagen-rich dietary ingredients, was added to a diet for cats. Zentek and Schulz [ 34 ] also found a higher renal Ox excretion when cats were fed diets based on collagen tissue when compared to diets based on soy protein isolate or horsemeat.…”

“…An increased renal Ox excretion by a high intake of animal protein might derive from an enhanced endogenous Ox synthesis from specific amino acids [ 32 ]. In a study by Dijcker et al [ 4 ], the addition of synthetic hydroxyproline to a diet resulted in an increased urinary Ox excretion in cats. Zentek and Schulz [ 34 ] also found a higher renal Ox excretion when cats received diets based on collagen tissue (rich in hydroxyproline) when compared to diets based on horsemeat or soy protein isolate.…”

“…The sample size, however, was based on previous studies in cats evaluating dietary effects on urinary and faecal parameters (e.g. [ 3 , 4 , 19 , 25 – 28 ]).…”

“…Results obtained when feeding a dry food might therefore not be transferable for the use of canned diets. As previous studies used experimental diets with low moisture concentrations [ 4 , 26 ], it was the aim of the present study to investigate the effects of varying protein concentrations and qualities in a canned diet on the urine composition of cats and to detect possible differences to the use of a dry food.…”

Study of ingredients and nutrient composition of commercially available treats for dogs

“…Rawhides, whose only ingredient is dried bovine skin, were the treats richest in Hyp, and recent indings suggest that the consumption of Hyp-containing protein sources should be discouraged for dogs prone to calcium-oxalate urolith formation. 20 A study by Dijcker and others 21 showed Hyp to be related to the synthesis of endogenous oxalate, a potential substrate in the formation of calcium-oxalate uroliths in dogs and cats. A recent study 20 involving cats demonstrated that collagen tissue-rich diets (collagen is the protein source in which Hyp is most concentrated) signiicantly increased urinary oxalate excretion proportionally to Hyp intake.…”