Degradability and digestibility of full-fat soybeans treated with different sugar and heat combinations

Two experiments were conducted to study the effects of different combinations of sugars and heating time and temperature on the ruminal undegradable protein fraction and DM digestibility of full-fat soybeans. In the first experiment, the influence of sugar addition before heating (none, soaked in either a high fructose corn syrup [HFCS] solution, lignosulfonate or molasses), micronization temperatures (100, 110, 120, and 130 °C), and temperature holding times (0, 30, 60, and 120 min) was examined in a 4 × 4 × 4 factorial arrangement of treatments. In the second experiment, the effect of heating in a sugar solution was studied in a 4 × 2 × 4 factorial design with four sugar treatments (none, soaked either in fructose, molasses or a high xylose product), two soaking temperatures (100 and 120 °C), and four soaking times (0, 60, 120, and 240 min). In vitro dry matter digestibility (IVDMD), in vitro ruminal undegradable protein (RUP), and in sacco RUP were measured. In the first experiment, increased temperatures and heating to 120 min resulted in an increased RUP fraction of full-fat soybeans with no effect on DM digestibility, relative to when no sugar or fructose was added. There was a decrease in digestibility with increased temperature when lignosulfonate or molasses was added and with increased heating time when lignosulfonate was added. In the second experiment where soaking in sugar and heating were done simultaneously, lignosulfonate increased the RUP of soybeans without affecting its digestibility but values were numerically lower than when soaking and micronizing were conducted in two different steps as performed in the first experiment. Key words: protein, degradability, digestibility, micronization