Ferreira, GonzaloTeets, Christy L.2020-12-072020-12-072020-102590-2873http://hdl.handle.net/10919/101032Objective: The objective of this study was to evaluate the production performance, nutrient digestibility, and income over feed cost (IOFC) of high-producing dairy cows consuming diets containing alfalfa or grass hays with either corn or wheat grain. Materials and Methods: Twenty-four Holstein cows were randomly assigned to 1 of 4 diets in a replicated 4 x 4 Latin square design with a 2 x 2 factorial arrangement of treatments (hay and grain types) and 21-d periods. Diets were formulated using a least-cost approach. To determine revenues from milk produced, the amount of ECM (kg-d(-1)) was multiplied by $0.303-kg(-1) (i.e., class III milk price; US Federal Milk Marketing Order 5). The cost of the ration provided by the formulation software ($-cow(-1).d(-1)) was divided by the predicted DMI (kg-cow(-1)-d(-1)) to obtain the cost of feed ($-kg(-1)), which was then multiplied by DMI (kg-cow(-1).d(-1)) to provide the actual daily feed cost ($.cow(-1).d(-1)). Results and Discussion: Cows consuming diets containing alfalfa hay consumed more DM than cows consuming diets with grass hay (27.1 vs. 24.4 kg-d(-1)). Cows consuming diets containing alfalfa hay produced more milk than cows consuming diets containing grass hay (47.5 vs. 44.7 kg-d(-1)). Milk from cows consuming diets containing grass hay had greater fat concentrations than milk from cows consuming diets containing alfalfa hay (4.22 vs. 3.89%). Using hay prices of $418 and $154-t(-1) respectively, for alfalfa and grass hays, diets containing grass hay resulted in greater IOFC than diets containing alfalfa hay ($8.39-d(-1) vs. $7.68-d(-1), respectively). Implications and Applications: Results of this study showed that IOFC can be supported when feeding grass hay using a least-cost ration formulation approach.application/pdfenCreative Commons Attribution-NonCommercial-NoDerivs 4.0 Internationalleast-cost formulationmanagementprofitabilitycost controlArticle - Refereedhttps://doi.org/10.15232/aas.2020-020233652590-2865