Master of Science (MS)


Animal Science (Animal, Dairy, and Poultry Sciences)

Document Type



Excess protein in dairy cattle diets unnecessarily increases the cost of production and may contribute to environmental pollution. The objective of this research was to evaluate the effect of feeding dairy cows with two levels of dietary protein on animal performance and manure characteristics. Two experiments were carried out with 24 lactating dairy cows each. Experiment 1 was corn silage based and had a control TMR (HP1) estimated to contain 16.5% CP with SBM and treatment TMR (LP1; 13.5% CP) using DDGS and rumen protected Lys and Met. Experiment 2 was ryegrass haylage based and had a control TMR (HP2) with 15.5% CP with Met and a treatment TMR (LP2) with 13.5% CP with Lys and Met. Experiments were analyzed as a crossover design using the MIXED procedure of SAS with pen as the experimental unit. Experiment 1 had no significant difference between treatments in DMI (21.0 for HP1 and 20.4 kg/cow/d for LP1; P=0.46) and milk yield (20.7 for HP1 and 20.5 kg/cow/d for LP1; P=0.91). Percentage of milk components averaged 4.21, 3.72, 4.54, and 9.15, respectively for fat, protein, lactose, and solids non-fat (P>0.60). Milk urea nitrogen (MUN) decreased (P<0.01) from 17.2 with HP1 to 9.93 mg/dL with LP1. Manure pH was significantly higher for HP1 than LP1 (7.87 and 7.53 respectively, P<0.05). Experiment 2 had no significant difference in cow performance (DMI: 21.4 for HP2 and 20.9 kg/cow/d for LP2; P=0.51; milk yield: 26.4 for HP and 24.4 kg/cow/d for LP2; P=0.19; percentage of milk components averaged 3.48, 3.29 and 4.71, respectively for fat, protein and lactose; P>0.30; MUN decreased (P<0.01) from 9.85 with HP2 to 6.40 mg/dL with LP2). Manure pH was significantly higher for HP2 than LP2 (7.50 for HP and 7.13 for LP, P=0.05). There was no difference in volatilized N between HP2 and LP2. This experiment suggests that performance of late-lactation dairy cows can be maintained with low-protein DDG based diets supplemented with Lys and Met.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Moreira, Vinicius R.