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Digestibility of Nutrients in Raw and Heated Soyflakes for Pigs¹

Texas Agricultural Experiment Station³, College Station 77843

Abstract

Raw, defatted soyflakes (SF) with an initial moisture content of 23%, were heated at atmospheric pressure for 25, 35, 45, 65 or 105 min in a 57-cm diameter French cooker with the steam jacket pressure maintained at 2.81 kg/cm². Heating for 25 min brought the SF to 100 C; thereafter, the temperature ranged from 100 to 107 C. In vitro measurements of the raw SF and the range for the heated SF were, respectively: trypsin inhibitors 31.1, 6.2 to 1.4 mg/g sample; urease 2.02, .48 to .05 ph; protein dispersibility index (PDI) 80.6, 29.6 to 7.7%; N solubility index (NSI) 76.9, 21.6 to 7.5%; Hunterlab color value (L) 79.9, 70.0 to 58.2; Hunterlab color value +a –1.9, 1.2 to 8.8. Thirty-six barrows, fitted with T-cannula near the terminal end of the ileum were used in six experimental periods (six pigs/period) to evaluate the raw and heated SF. Diets were cornstarch based, with SF being the only protein source. Heating SF for 25 to 105 min greatly improved (P<.01) N, amino acid and energy digestibility, N retention and pig performance. Comparisons among the heated SF were nonsignificant (P<.10), indicating that heating periods greater than 25 min neither improved nor worsened these values. Of the essential amino acids, tryptophan digestibility was improved the most by heating. Selected small intestine digestibilities for the raw and mean of the heated SF were, respectively: N 35.1, 79.4%; tryptophan 24.8, 76.8%; lysine 44.2, 85.1%; methionine 46.7, 81.8%. Differences in nutrient digestibility between raw and heated SF were greater at the end of the small intestine than over the total tract, due to increased degradation of nutrients from raw SF in the large intestine. This response suggests that the factors present in raw SF responsible for reduced small intestine digestibility were not as active in the pig's large intestine.

¹ T.A. 18342, Texas Agr. Exp. Sta. This study was financially supported by the American Soybean Assoc, St. Louis, MO.

² Current address: Anim. Sci. Dept., Univ. of Georgia, Athens 30601.

³ Dept. of Anim. Sci.