Effect of replacement of barley meal with crude glycerol on lactation performance of primiparous dairy cows fed a grass silage-based diet

The use of increasingly available glycerol, from the biodiesel industry, in dairy cow diets was assessed. The effects of replacement of barley meal by crude glycerol in a total mixed ration based on the grass silage on dry matter intake, milk yield and composition, rumen pH, silage degradability and metabolic status in mid-lactation Holstein dairy cows were evaluated. Eight, tie-stalled, primiparous cows were assigned to a 4×4 Latin square experimental design with two cows per treatment. Cows were paired according to milk yield and body weight, with one ruminally cannulated cow in each pair. The treatment period lasted 21 days of which 16 days were for adaptation. Cows were given a total mixed ration where barley meal was replaced isoenergetically by 0 kg (control), 1 kg, 2 kg and 3 kg crude glycerol per day per cow. An increased level of crude glycerol in the diet increased total intake (P<0.001). Milk yield and composition were not affected by glycerol inclusion to the diet, with the exception of an increase in the milk protein content (P<0.001). Cows given the glycerol diet had lower concentrations of blood nonesterified fatty acids (P=0.038) and a higher concentration of blood urea (P<0.001). Partial replacement of barley meal with crude glycerol in a total mixed ration affected the rumen environment, as the proportions of volatile fatty acids changed. There were no effects of treatment on the effective degradability of silage nutrients. These results indicate that crude glycerol is a suitable replacement for barley meal in a total mixed ration based on grass silage with no detrimental effect on lactation performance or rumen parameters.