Total body water in farm animals

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Abstract
Dilution procedures with tritium and labeled and unlabeled pyrazolones were used to measure total body water in 89 swine, 99 cattle, and 170 sheep, grouped for convenience of presentation into two age-weight groups. Mean plasma disappearance rates for injected antipyrine were 45, 23, and 28%/hr, and loss of antipyrine reversibly bound to plasma protein was 35, 22, and 32% for swine, cattle, and sheep, respectively. Greatest loss of the test substances was via the urine. Total body-water values were significantly higher (P < 0.05) in ruminant animals than in swine, and observed age differences were greater (P < 0.01) than differences between methods. Results favored tritium as the indicator of choice because of its rapid equilibration with body water, slow plasma protein binding, and decreased metabolic breakdown. Concurrent use of two or more indicators having different volume distributions offer advantages for use in ruminant animals over monogastric animals for the correction of body composition data for gastrointestinal water.