Tritiated water for estimating total body water and water turnover rate in birds

Abstract

The use of tritiated water (TOH) to estimate total body water (TBW) and total water turnover rate was validated in chukar partridges (Alectoris chukar) and sand partridges (Ammoperdix heyi). For six chukar partridges weighing between 315 to 475 g, TOH equilibration with body fluids was less than 45 min after intramuscular or intravenous injections. Mean TOH space in eight chukar partridges was 99.8% of the mean TBW measured by desiccation with individuals ranging between 97.9 and 103.2%. TOH space best approximated TBW when TBW was calculated by using the mean body mass for a bird weighed at TOH injection and at TOH equilibration. Total water intake as estimated by TOH ranged between 90.7 and 113.3% of measured water intake in three sand and three chukar partridges, birds ranging in mass from 145 to 446 g. We conclude that the TOH method provides accurate estimations of TBW and water turnover rates in birds. For birds of up to 500-g body mass, we recommend 45 min for TOH equilibration with body fluids, and intramuscular injections of 0.05 muCi TOH/g body mass for TBW estimations and 0.1 muCi TOH/g body mass for water turnover estimations.

Validation of Water Flux and Body Composition in Glaucous Gulls (Larus hyperboreus)

“…After blood sampling, the bird was then placed back into its run. Previous research has shown that 120 min is sufficient for HTO to equilibrate with body water in birds (Degen et al 1981;Gales 1989;Kirkwood and Robertson 1997;Shaffer et al 2001b). Therefore, we were con fident that isotopic water had completely mixed with the gulls' body water.…”

“…Specific activity of tritiated body water was determined in trip licate by scintillation spectrometry (Beckman LS 6500, Beckman Coulter, Fullerton, CA) of water obtained from serum using the freeze-trap method (Ortiz et al 1978). TBW (g) was calculated from the initial and final dilution of isotopic water injected into a bird (Degen et al 1981). Total water influx (TWI) and efflux (TWE) were calculated from the turnover of isotopic water using Equations (4) and (6) of Nagy and Costa (1980), assuming a linear change in body mass.…”

“…Despite its widespread application (see Nagy and Peterson 1988), only a modicum of validation studies have quantified the errors in water turnover measured isotopically compared with direct measures of water intake (Nagy and Costa 1980;Degen et al 1981;Costa 1987;Gales 1989;Robertson and Newgrain 1992;Lea et al 2002;Salatas et al 2002;Gessaman et al 2004). Fewer validation studies have measured water flux when animals were allowed to consume both food and water (Degen et al 1981;Costa 1987;Gessaman et al 2004).…”

“…Although there is an abundance of measurements comparing both methods in mammals, fewer studies have quantified the errors between methods in birds (e.g., Degen et al 1981;Crum et al 1985;Green and Brothers 1989). This is surprising, given that body water content has been measured by whole body desiccation or complete homogenization of car casses in several bird species (Mahoney and Jehl 1984;Parker and Holm 1990;Ellis and Jehl 1991;Janes 1997).…”

“…This is surprising, given that body water content has been measured by whole body desiccation or complete homogenization of car casses in several bird species (Mahoney and Jehl 1984;Parker and Holm 1990;Ellis and Jehl 1991;Janes 1997). Moreover, bird feathers are not part of the exchangeable water pool and thus do not equilibrate with tritiated water (HTO; Degen et al 1981). Hence, this may lead to overestimates in TBW deter mined with isotope dilution.…”