Alfalfa leaves as a protein source: Replacement value of alfalfa leaves for soybean-meal protein in forage-based diets fed to mature ewes

Abstract

Four ruminally and duodenally cannulated mature ewes (BW65.8  4.6kg) were used in a 4x4 Latin square designed experiment to investigate the replacement value of alfalfa leaves (AL) for soybean meal (SBM) protein.  Ewes received basal diets consisting of bromegrass hay, cracked corn, and one of four protein supplements.  Diets were formulated to be isonitrogenous by replacing SBM with AL on a nitrogenous basis.  Supplement treatments were 100% SBM; 33.3% AL and 66.7% AL and 33.3% SBM and 100% AL.  Experimental periods were 14 days with 10 days of diet adaptation followed by 4 days of ruminal, duodenal, and fecal sample collection.  Replacing SBM with AL decreased intake of OM and NDF (quadratic; P<.02). Intake of N increased as AL replaced SBM, which resulted in a cubic effect (P=.06).  Organic matter flow and tru ruminal OM digestibility were not affected (P.18) by replacement of SBM with AL.  Lower and total tract OM digestibility increased from the 33.3% AL to the 66.7% AL diet and decreased from the 66.7& AL to the 100% AL dietary treatment resulting in cubic effects (P=.01 and .03, respectively).  Nitrogen flow and true ruminal N digestibility were not influenced (P.18) by supplemental protein treatment.  Greater lower tract N digestibility for 33 and 67% AL resulted in a quadratic effect (P=.05, whereas total tract N digestibility was not affected (p.13) by replacing SBM with AL.  No treatment differences (P.20) were detected for NDF flow or ruminal NDF digestibility.  Digestibility of NDF entering the small intestine tended to respond quadratically (P=.09) with a tendency for a cubic effect (P=.08) for tor total tract NDF digestibility as a result of greater digestibility of 66.7% ALdiet.  Ruminal pH increased quadratically (P=.0004), while ruminal NH₃, N tended _to decrease linearly (p=.10) as AL replaced SBM.  Ruminal particulate and fluid passage rates were not influenced (P .21) by replacing SBM with AL.  Total VFA concentrations within the rumen decreased in a quadratic (P=.05) fashion.  Acetate:propionate ratio responded quadratically (P=.0001) due to higher acetate:propionate ratios for diets containing a combination of supplementary protein. Alfalfa leaves can replace soybean meal as a protein supplement; however, greater nutritional value was apparent when the two protein sources constituted the supplement.