Responses in Milk Yield, Milk Composition and Rumen Fermentation in Lactating Cows Receiving a Corn Straw or Mixed Forage Diet

An experiment was conducted to investigate responses in milk production, milk composition and rumen fermentation of dairy cows receiving a corn straw or mixed forage diet. Ten primiparous and rumen-cannulated Holstein dairy cows averaging 127 +/- 13 days in milk (mean +/- SD) were randomly assigned to CS (37.1% corn straw as sole forage) or MF diet (3.7% Chinese wildrye+28.4% alfalfa hay+26.5% corn silage as mixed forage). Feed intake, body weight, body condition score and milk production were monitored. Milk fat, protein, lactose and total solids were analyzed by near-infrared analysis. Samples of rumen fluid were collected via cannula every 6 h over a 72 h duration to analyze pH, ammonia-N and VFA concentrations. Results showed that cows fed MY diet significantly increased dry matter intake (p<0.01) as well as yields of milk (p<0.05), 4% FCM (p<0.01), milk fat (p<0.05), lactose (p<0.05) and total solids (p<0.05). Cows fed MF diet had higher (p<0.01) ruminal acetate concentrate and ratio of acetate to propionate and lower concentrations of ammonia-N (p<0.01), propionate (p<0.05), butyrate (p<0.01), isobutyrate (p<0.01), valerate (p<0.01) and isovalerate (p<0.01) than cows fed CS diet. Collectively, these results suggest that cows fed MY diet improve DMI and milk production. In addition, cows fed CS diet had minor differences in rumen pH and total VFA concentration which may suggest that corn straw played an important role in maintaining rumen function when cows were fed this higher concentrate diet.