Effect of Heat Treatment on Protein Quality and Utilization of Soybean and Sunflower Meals by Dairy Cattle

Effect of heat treatment on soybean and sunflower meal proteins were studied using in vitro and in vivo techniques. In experiment I, soybean meal (SBM) and sunflower meal (SFM) were subjected to steam heating about 120 C for 25 to 30 seconds using a commercial cooker extruder. The heat treatment was designed to reduce solubility of the SBM and SFM in the rumen, thereby allowing more soybean meal protein and sunflower meal protein to be undigestible in the rumen but still digestible in the lower digestive tract when fed to cattle. Solubilities of protein in SBM and SFM were reduced (P\u3c .001) by the heat treatment. The protein solubility in SBM, heated soybean meal (HSBM), SFM and heated sunflower meal (HSFM) were 17.0, 12.4, 29.9 and 19.3%, respectively. Concentrations of amino acids in the soluble fraction of HSBM were reduced as compared with SBM, but those in HSFM were not altered. Percent of essential amino acids in the soluble fraction of the two protein supplements were reduced more than nonessential amino acids. A growth assay with mice showed that heat treatment did not reduce the quality of proteins in the oil meals. In experiment II , young dairy calves were used in a 12-week feeding period to evaluate the effect of the heat treatment of SBM and SFM on animal performance. Weight gains, feed consumption, and feed efficiency of calves fed SBM, HSBM, SFM and HSFM diets were about equal. Average weight gains for the 12-week experimental periods were .61, .63, .60 and .62 kg/day, respectively. A digestion trial with 12 week old male calves showed no differences in digestibility of the four rations. However, cofficients [sic] of digestibility of the SBM diet were slightly higher for all nutrients as compared with HSBM. Blood urea concentrations measured at various times after feeding the experimental rations were not statistically different. Eighteen Holstein cows were used in experiment III to evaluate the effect of SBM versus HSBM on milk production and composition in a 16-week lactation trial. Cows receiving HSBM produced more milk (P\u3e .05) during the first 8 weeks of the lactation period, than cows on SBM ration, but production was not greater in the later part of lactation when protein intake by both groups was more than adequate. Percent of milk components were similar in both groups. Dry matter intake and body weight gains were about equal in both treatments. Blood urea nitrogen and urine nitrogen in cows fed SBM were not different from those fed HSBM. However, the values were lower in HSBM-fed cows. Heat treatment of SBM did not alter the profile of amino acids in the arterial or venous blood serum of cows nor affect amino acid uptake by the mammary gland