Effects of Heat Treatment on the Metabolizable Energy Value of Soybeans and Extracted Soybean Flakes for the Hen

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Abstract
The effects of graded levels of heat treatment of ground soybeans and extracted dehulled soybean flakes (autoclaving 10, 40, or 60 minutes at 107°C, or 120 minutes at 120°C) on their utilization by adult hens were studied by measurement of metabolizable energy and fat absorbability. In general, the effects observed were similar to those previously obtained in studies with young chicks. The metabolizable energy values of the unheated materials were markedly and significantly lower than those of the optimally heated samples. Prolonged heating reduced the energy value of extracted flakes, but had little or no deleterious effect on the energy value of ground soybeans. The metabolizable energy values of the optimally heated soybeans and extracted flakes for hens were in close agreement with those reported for chicks. Absorbability of dietary fat was impaired by unheated extracted flakes, and this effect was abolished by heat treatment. Absorbability of soybean oil in ground soybeans was also impaired to about the same extent, but was not consistently improved by heat treatment. The possible existence of a specific factor which interferes with fat utilization was discussed. Under the conditions of these experiments, egg production was reduced by feeding unheated soybeans or extracted flakes as the sole source of protein.