Intake, Digestibility, and In Situ Digestion Kinetics of Treated Wheat Straw and Alfalfa Mixtures Fed to Holstein Heifers

Twelve Holstein heifers averaging 370 kg of BW (4 animals fitted with permanent ruminal cannulas and 8 intact animals) were used in three replications of a 4 × 4 Latin square design to determine effects of feeding combinations of alkaline hydrogen peroxide-treated wheat straw and alfalfa haylage on ad libitum nutrient intake and digestibility and ruminal characteristics. A second experiment was conducted simultaneously to determine effects of feeding combinations of these forages on in situ digestion kinetics of both treated wheat straw and alfalfa. Diets consisted of an 80:20 forage to concentrate ratio (DM basis), and dietary designations were based on DM ratios of treated wheat straw:alfalfa haylage. Positive associative effects were noted for both DM and OM intakes due to addition of alfalfa; greatest increases occurred when the lowest (27%) level of alfalfa was added. Dry matter and OM intakes increased by 12 and 14%, respectively, when diet 53:27 was compared with diet 80:0. Digestibility of OM was similar across diets, averaging 63.6%. Associative effects were not noted for total tract fiber digestibilities. Positive associative effects of combinations of the forages were noted for in situ rates of disappearance of DM, NDF, and certain hemicellulose neutral monosaccharides (arabinose, galactose, mannose, and xylose) of both treated wheat straw and alfalfa haylage. Apparent discrepancies between in vivo and in situ data may have been due to compensatory hindgut fermentation masking improvements in ruminal digestibility when combinations of the forages were fed.