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Addition of glycerol to lactating cow diets stimulates milk protein yield to a greater extent than addition of corn grain
As the biofuel industry grows and expands, there is an increased availability of the by-product glycerol, which could be a glucogenic feedstuff for dairy cows. The objective of this study was to determine if the addition of glycerol to the diet of dairy cows would stimulate milk protein yield in the same manner as the addition of corn grain. Twelve lactating dairy cows were assigned at 81 ± 5 DIM to 3 diets in a repeated 3 x 3 Latin square design. The diets were a 70%-forage diet considered the base diet, the base diet with 19% ground and high-moisture corn replacing forages, and the base diet with 15% refined glycerol and 4% added protein supplements to be isocaloric and isonitrogenous with the corn diet. Diets contained 17.2, 17.9, and 17.3% CP, respectively, and 34, 28, and 30% NDF, respectively. The diets were fed for periods of 28 days each, and milk, feed and blood samples were collected during the last week of each period for compositional analysis. Treatment differences were evaluated by ANOVA using PROC MIXED of SAS with cow as a random effect. Dry matter intake increased from 23.7 kg/d on the base diet to 25.8 kg/d on the corn diet (P = 0.007) and to 27.2 kg/d on the glycerol diet (P < 0.001). There was a tendency for DMI to be higher with glycerol than corn (P = 0.06). Milk production increased from 39.2 kg/d on the base diet to 43.8 kg/d on the corn diet (P < 0.001) and to 44.2 kg/d on the glycerol diet (P < 0.001). There was no difference in milk yield between corn and glycerol diets. Milk protein content was 3.19, 3.33, and 3.44% on the base, corn and glycerol diets, respectively, and the stimulation by glycerol was greater than the stimulation by corn (P = 0.037). Protein yield was increased 197 g/d by the addition of corn and 263 g/d by the addition of glycerol, and the glycerol effect was larger than the corn effect (P = 0.054). Efficiency of capture of dietary protein in milk protein, however, was lower on the glycerol diet at 29.5% compared to 32.6% on the corn diet (P = 0.017). It was concluded that glycerol stimulated milk protein yield to a greater extent than corn grain.
Keywords:
glycerol, milk protein synthesis, dairy cow