Effects of Oscillating Crude Protein Content of Dairy Cow Diets
By:Alston Neal Brown,OhioLINK Electronic Theses and Dissertations Center
Published on 2014 by
Overfeeding crude protein (CP) is a common practice in the dairy industry because it reduces the risk of a loss in milk; however, overfeeding CP can increase feed costs and negatively impacts the environment. We hypothesized that oscillating dietary CP concentrations over 2-d periods to equal the average concentration of a diet limiting in metabolizable protein (MP) for lactating dairy cows would improve milk protein yield and nitrogen use efficiency (NUE) over a diet limited in MP because oscillation should stimulate nitrogen (N) recycling to the rumen. Twenty-one Holstein dairy cows averaging 117 DIM were assigned to a treatment sequence in seven 3x3 Latin Squares with 28-d periods. The Positive Control contained 16.4% CP (MP allowable milk = 45.4 kg/d based on treatment mean DMI), the Negative Control contained 13.4% CP (MP allowable milk = 28.6 kg/d), and the Oscillating treatment consisted of a diet with 10.3% CP fed for 2 d followed by a diet with 16.4% CP fed for 2 d repeated over the 28-d period to average 13.4% CP. To determine how long (or if) cows would respond to the lowest CP diet (10.3% CP), 8 additional Holstein cows were fed the 10.3% CP diet for 5 d. Milk yield for cows fed the 10.3% CP diet decreased compared to cows fed the Positive Control beginning on the second day the 10.3% CP diet was fed, indicating that the diet was deficient in MP. Milk yield was similar for cows fed the Negative Control compared to cows fed the Positive Control. Because milk yield was similar for cows fed the Positive Control and Negative Control, the 13.4% CP treatments (Negative Control and Oscillating treatment) may have met the MP requirements of the cows; therefore, interpretation of whether or not oscillation would improve milk yield, milk protein yield on NUE over a diet limited in protein is restricted. Milk urea nitrogen (MUN), NUE, urinary N (UN; % of N intake), fecal N (% of N intake) were similar for cows fed the Oscillating treatment and cows fed the Negative Control. There was a trend for a decrease in energy corrected milk (ECM) and milk protein and milk fat yields for cows fed the Oscillating treatment compared to cows fed the Negative Control. Milk yield decreased from the first day to second day cows on the Oscillating treatment were fed the 10.3% CP diet, explaining the trend for a reduction in milk protein yield and indicating that 2 d may have been too long for the diets to be fed before being switched. Oscillation at most maintained milk yield, milk protein yield, and NUE compared to the Negative Control.
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