Influence of Ruminally Undegraded Protein and Zinc Methionine on Milk Production, Hoof Growth and Composition, and Selected Plasma Metabolites of High Producing Dairy Cows

Thirty-six first or later lactation Holstein cows were grouped according to their 305-d mature equivalent milk yield and used in a 240-d 2 × 3 factorial design experiment. Objectives were to determine the effect of supplemental Zn-Met and ruminally undegraded protein (RUP) on milk production, hoof growth and composition, and selected plasma metabolites of high producing dairy cows. During the dry period, cows received rations supplemented with 1) ZnSO4 (DT1) or 2) Zn-Met (DT2). Treatments during lactation were 1) soybean meal (SBM) (LT1), 2) ZnSO4-treated SBM (LT2) (Consolidated Nutrition L. C., Ft. Wayne, IN), and 3) ZnSO4-treated SBM plus supplemental Zn-Met (LT3) (Zinpro Corp., Eden Prairie, MN). All rations were formulated to contain equal amounts of Zn. Cows receiving DT1 had higher 3.5% fat-corrected milk (FCM) and milk fat percentage when compared with those receiving DT2 (P<0.05). Hoof growth was greater during the dry period for cows receiving DT2 (0.22 mm/d) than for those receiving DT1 (0.20 mm/d). The ZnSO4-treated SBM and LT3 had no effect on hoof growth during lactation. Mean hoof CP content was lowest at peak lactation (85.6%) and highest at calving (90.4%). Cows receiving LT3 had the highest hoof Zn content during lactation. Glucose was higher later in lactation and at feeding; whereas, insulin and plasma essential amino acids (AA) were highest at peak lactation. For high producing dairy cows, especially those with hoof problems, supplemental RUP and Zn-Met may provide nutrients needed for hoof growth and increase production by helping maintain hoof health and DMI.