Validation of saliva and urine use and sampling time on the doubly labelled water method to measure energy expenditure, body composition and water turnover in male and female cats

Less invasive protocols are necessary to study energy expenditure (EE) of cats living in homes for expressing their normal living conditions. The present study compared sampling times and the use of saliva, urine and blood to measure(2)H and(18)O to apply the doubly labelled water method. In the first study, four cats were used to evaluate the enrichment (2, 4, 6, 7 and 8 h) and elimination (2, 4, 6, 8, 10, 12, 14, 16, 18 and 20 d) of(2)H and(18)O (subcutaneously injected). The maximum enrichment was after 5 h (R(2)0 center dot 82) of injection, with an Ln linear elimination of both isotopes (P< 0 center dot 001;R(2)0 center dot 99). The results of EE were similar, regardless of the sampling time used (P= 0 center dot 999). In the second study, seven male cats and seven female cats were used. Before and after isotope injection (5 h, 7 d, 10 d and 14 d), blood, saliva and urine were collected. Isotope enrichment was lower in urine (P< 0 center dot 05) and at the similar level in blood and saliva. Isotope elimination was similar for all fluids (P< 0 center dot 473). The EE calculated with blood and saliva was similar but higher for urine (P= 0 center dot 015). According to Bland-Altman statistics, blood and saliva presented low bias and high correlation (P< 0 center dot 001), but this was not observed for urine (P= 0 center dot 096). Higher EE was observed for male cats (384 (se39) kJ/kg(0 center dot 67)per d) than for female cats (337 (se34) kJ/kg(0 center dot 67)per d;P< 0 center dot 05). The sampling time for the method is flexible, and saliva can be used as a substitute for blood. (AU)