SYNOPSIS. A hypothesis generated from field observations of lions and tigers was tested in a zoo setting. The presence of a whitish material in urine marks, detected by visual inspection, led to the surmise that analsac secretions were expelled along with urine. This hypothesis was evaluated by labelling anal-sac secretions of various felids with an inert dye. The animals were monitored thereafter for signs of dye in urine-marks, on feces or in their enclosures. The failure to find anal-sac secretions in urine or on feces led to a search for an alternate explanation for the whitish material. A likely answer was found in the confirmation of considerable lipid in the bladder urine of lions and tigers, which separates to form a visible, whitish layer. Relative levels of urinary lipid reflect general condition of an animal as they correlate with kidney fat reserves (Hewer et al. , 1948), so the amount of lipid in a scent mark could serve as an indicator of condition. Furthermore, because lipid retards the release of volatile compounds (Regnier and Goodwin, 1976), lipid in a scent mark will extend release time of a pheromonal message.
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A 1993 study studied this question.