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Determination of Specific Gravity by Air Displacement¹

Michigan Agricultural Experiment Station,³ East Lansing

Abstract

A technique was developed for the determination of body volumes of living animals by air displacement. Two experiments were reported in which body volumes were determined at two levels of negative pressure. In the first experiment, specific gravity of 23 adult female guinea pigs, calculated from body volumes determined at a total vacuum of 320 mm. of Hg., were correlated with carcass fat, water, protein and ash. The correlation coefficients were –.70, 0.67, 0.68 and 0.58, respectively. In the second experiment, body volumes of 25 female guinea pigs were determined at a total vacuum of 120 mm. of Hg., employing a constant volume method of manometeric measurement. Correlation coefficients for air specific gravities thus obtained and carcass fat, water, protein and ash were –.82, 0.81, 0.72 and 0.72, respectively. Other factors which influenced the accuracy of the body volume determinations were changes in chamber temperature and humidity. Variations due to the contents of the digestive tract and composition of the viscera did not significantly alter the relationship between air specific gravity and carcass composition.

¹ Journal Article No. 2010, Michigan Agricultural Experiment Station.

² This is a portion of research completed for the Ph.D. thesis by the senior author.

³ Departments of Animal Husbandry, and Physiology and Pharmacology.