Effects of Dietary Protein on Blood, Urine, and Milk Composition

Abstract

SUMMARY Three groups of 10 cows each were fed low-protein (8.9%), medium-protein (11.3%), and high-protein (14.2%) grain rations to determine the effects of different percentages of dietary protein intake on blood urea nitrogen ( bun ), urinary urea nitrogen ( uun ), urinary nitrogen ( un ), and urinary creatinine ( uc ) concentrations, milk production, milk composition, and body weight. Cows fed the low-protein ration consumed 123 and 107% of National Research Council (NRC) requirements for protein and energy, respectively; those fed the medium-protein ration consumed 137 and 110%, and those fed the high-protein ration consumed 157 and 107%. During the 9 weeks’ feeding, bun , uun , un , and uc concentrations and milk production, milk protein, and body weight were significantly (P < 0.01) affected by treatment. Mean bun , uun , and un concentrations were increased in the cows having the higher levels of protein intake. Mean uc concentration was highest in the cows fed the low-protein ration, indicating use of body protein. Cows fed the rations with the higher protein content were more persistent (decreased more slowly) in milk production.