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RUMEN PROTECTED SOY PRODUCTS FOR DAIRY COWS Ignacio R. Ipharraguerre, Jimmy H. Clark, and David E. Freeman TAKE HOME MESSAGES • Passage of feed protein to the small intestine of lactating dairy cows fed protected soy protein supplemented diets that contain 18% crude protein may be increased compared with solvent-extracted soybean meal (SSBM) supplemented diets without significantly affecting the supply of microbial protein. • Significant improvements in the supply of methionine and lysine, especially methionine, should not be expected when SSBM is partially replaced with protected soy proteins in the diet. INTRODUCTION Under conventional feeding conditions, an inadequate amount or pattern of essential amino acids (EAA) absorbed from the small intestine of dairy cows may be partly responsible for creating or aggravating inefficiencies in the postabsorptive metabolism of nitrogen. Selection of the proper source of supplemental crude protein (CP) for feeding offers an excellent oportuntity for influencing the supply of amino acids (AA) to dairy cows. Extensive degradation of protein by ruminal microbes can compromise their value for contributing quantitatively and (or) qualitatively to the supply of EAA that becomes available to dairy cows. Some of the most effective methods for decreasing the ruminal degradability of soy proteins that are approved for commercial use involve the controlled administration of heat to soybeans [i.e., expeller, processed soybean meal (ESBM) and whole roasted soybeans (WRSB)] or heat plus reducing sugars to soybean meal (NSBM). The impact of heat-treated soy-protein supplements on the ruminal outflow of nitrogen (N) and carbohydrate fractions have not been compared in the same study with lactating dairy cows. The objectives of this study were to compare the effects of partially replacing SSBM with ESBM, NSBM, or WRSB in the diet of lactating dairy cows on ruminal fermentation, passage of nutrients to the small intestine, and nutrient digestibility. MATERIALS AND METHODS Four multiparous lactating Holstein cows fistulated in the rumen and duodenum that averaged 209 d in milk were used in a 4 x 4 Latin square design to evaluate the practical replacement of solvent SSBM with soy-protein products of reduced ruminal degradability. On a dry matter basis, diets contained approximately 15% alfalfa silage, 25% corn silage, 34.3 to 36.9% corn grain, and 22.0% soy products, plus minerals and vitamins; 18.2% crude protein, 25.5% neutral detergent fiber, and 35.3% starch. In the experimental diets, SSBM was replaced with ESBM, NSBM, or WRSB to supply 10.2% of the dietary dry matter (Table 1). RESULTS AND DISCUSSION Intakes of dry matter, organic matter, acid detergent and neutral detergent fiber, and starch were unaffected by the source of soy protein (Table 2). Likewise, true ruminal fermentation of organic matter and apparent digestion of fiber fractions and starch in the rumen and total tract were not significantly altered by treatments. Intake of N ranged from 567 (WRSB) to 622 g/d (ESBM), but differences among soy protein supplements were not significant (Table 3). Compared with SSBM, the ruminal outflow of nonammonia N was higher for NSBM, tended to be higher for ESBM, and was similar for WRSB. The intestinal supply of nonammonia nonmicrobial N was higher for NSBM and WRSB and tended to be higher for ESBM than for SSBM. However, no differences were detected among treatments when the flow to the duodenum of nonammonia nonmicrobial N was expressed as a percentage of N intake or nonammonia N flow. The ruminal outflow of microbial N, methionine, lysine, isoleucine, and valine were not significantly altered by the source of soy protein. Differences in ruminal outflow of arginine, histidine, leucine, phenylalanine, threonine, total essential AA, and total AA depended upon the source of soy supplements fed to the cows (Table 3). Nitrogen digested postruminally and in the total tract were not affected by source of soy protein. These findings suggest that partially replacing SSBM with ESBM, NSBM, or WRSB may increase the quantity of feed protein that reaches the small intestines of dairy cows. However, significant improvements in the supply of previously reported limiting amino acids (methionine and lysine) for milk production, particularly of methionine, should not be expected. Table 1. Protein ingredient and composition of the experimental diets (DM basis). Item Protein Soybean meal Solvent-extracted (49% CP), % Expeller2, % Heat-xylose-treated3, % Whole roasted soybeans4, % Chemical DM, % CP, % NDF, % ADF, % Starch, % Ether extract5, % NEL, Mcal/kg of DM5 SSBM Treatments1 ESBM NSBM WRSB 19.42 … … … 10.10 10.20 … … 9.20 … 10.20 … 11.80 … … 10.20 66.5 18.2 24.2 13.3 35.3 2.9 1.67 66.8 18.1 25.4 13.3 34.8 3.6 1.67 66.7 18.2 27.1 13.3 35.8 3.0 1.66 66.8 18.3 26.5 13.8 33.7 4.6 1.73 ESBM = Expeller soybean meal, NSBM = heat-xylose treated soybean meal, SSBM = solventextracted soybean meal, WRSB = whole roasted soybeans. 2SoyPLUS® (West Central Cooperative, Ralston, IA). 3Soy Pass® (Ligno Tech USA, Inc., Rothschild, WI). 4Vita Plus Corp., Madison, WI (Protein dispersibility index = 8.96). 5Calculated using NRC model (2001), chemical composition of ingredients, and least squares means for intakes for each treatment as presented in Table 2. 1 Table 2. Intake and digestibility of energy components of the diet. Treatments1 Item SSBM ESBM NSBM WRSB --------------- (lbs/day) --------------Dry matter intake 43.6 47.1 46.0 42.7 Apparently digested total tract 30.8 33.7 33.3 30.6 Organic matter intake 40.3 43.4 42.3 39.6 Truly digested in rumen 22.2 22.2 21.6 21.1 Apparently digested postruminally 16.5 18.7 15.9 16.1 Apparently digested total tract 29.1 31.7 31.1 28.9 Acid detergent fiber intake 5.7 6.4 5.7 5.7 Apparently digested in rumen 2.9 3.3 2.9 2.6 Apparently digested total tract 1.8 2.2 2.0 2.0 Neutral detergent fiber intake 10.6 11.9 11.5 10.8 Apparently digested in rumen 5.3 6.2 5.5 5.7 Apparently digested total tract 4.2 5.3 5.3 5.1 Starch intake 15.4 17.0 16.3 14.1 Apparently digested in rumen 8.8 10.4 9.3 8.8 Apparently digested postruminally 6.2 5.7 6.2 4.8 Apparently digested total tract 14.8 16.3 15.6 13.7 1 ESBM = Expeller soybean meal, NSBM = heat-xylose treated soybean meal, SSBM = solvent-extracted soybean meal, WRSB = whole roasted soybeans. Table 3. Nitrogen (N) intake and digestibility and amino acid passage to the small intestine. Item SSBM Treatments1 ESBM NSBM WRSB N intake, g/d 579 622 613 567 Passage to duodenum Total N, g/d 502 543 590 529 b ab a 514 564 498b Nonammonia N, g/d 467 b ab a Nonammonia nonmicrobial N, g/d 222 283 323 289a % of NAN 48.4 56.0 58.5 57.9 % of N intake 40.0 47.4 56.0 51.0 Microbial N, g/d 245 227 236 209 N digested postruminally, g/d 344 372 409 354 N apparently digested total tract, g/d 421 450 440 393 % 72.3 72.8 71.9 69.0 Passage to small intestine, g/d 124b 155a 141a Arginine 121b c bc a Histidine 55 57 69 61ab Isoleucine 139 135 167 151 Leucine 229c 240bc 280a 245b Lysine 166 164 197 186 Methionine 58 59 64 61 c bc a Phenylalanine 127 132 159 141ab Threonine 112b 118b 133a 121b Valine 155 151 185 171 Total essential amino acids 1163b 1179b 1409a 1279ab 1 ESBM = Expeller soybean meal, NSBM = heat-xylose treated soybean meal, SSBM = solvent-extracted soybean meal, WRSB = whole roasted soybeans. a,b,c Values within the same row with uncommon superscripts are different (P<0.05).