THE NUTRITIONAL VALUE AND TRYPSIN INHIBITOR CONTENT OF PROCESSED SOYBEANS FOR LAMB MILK REPLACERS

Abstract

Full-fat soybean flour (FFSF) was prepared from dehulled soybeans by extraction with water and NaHCO3, colloid milling, cooking and spray-drying. The apparent destruction of soybean trypsin inhibitor (SBTI) prior to cooking was variable. A rat bioassay for SBTI was conducted with diets containing 1.6% nitrogen from cooked and uncooked FFSF. Cooking the FFSF for 1 h markedly improved rat growth (4.0 vs. 2.6 g/day, P < 0.01) and weight gain/protein intake (3.3 vs. 2.5, P < 0.01). The cooked FFSF was also used in three lamb experiments to supply 0, 30, 50 or 60% of the nitrogen in milk replacers. Apparent digestion coefficients for energy were 88, 92 and 92% (P < 0.05), and for nitrogen were 94, 95 and 92% for lambs fed milk replacers containing 0, 30 or 60% of the nitrogen from FFSF. The percent of total nitrogen intake retained was 61, 63 and 55, respectively. The lower energy digestion by lambs on the zero FFSF diet was attributed to the fat being supplied only by tallow. In another experiment, when unrefined soybean oil, equal to that supplied by FFSF, was used in place of the tallow in an all-milk protein milk replacer, energy digestion by lambs was greater than with a milk replacer containing FFSF. Milk replacers containing a mixture of spray-dried skim milk and whey powders resulted in higher nitrogen digestion and retention by lambs than did a mixture of roller-dried buttermilk and whey powders, when 50% of the nitrogen was supplied by FFSF. It was concluded that milk replacers containing up to 60% of the total dietary nitrogen from FFSF were utilized satisfactorily by milk-fed lambs.