A striking difference between the hays was the relationship between milk production and diet NDF concentration. For the orchardgrass-based TMRs, milk production declined approximately 1 pound/cow/day per unit increase in total diet NDF from 30 to 40 percent DM. For the alfalfa-based TMRs, milk production declined approximately 2.7 pounds/cow/day per unit increase in total diet NDF from 29 to 36 percent DM. Note, however, that alfalfa's greater rate of decline in milk production was due largely to substantially lower production at 35 percent alfalfa vs. all lesser alfalfa inclusion levels.
Milk composition and body weight were unaffected by hay type and amount; averaging 3.8 percent milk fat, 3.0 percent milk protein, 4.7 percent milk lactose, 6.9 lb body weight change, and 1.9 feed efficiency.
In conclusion, in this eight-week study with one orchardgrass hay and one alfalfa hay lot fed to Holstein dairy cows, grass and alfalfa hay had similar replacement values for corn grain and soybean. These results support previous research indicating that good quality grass forage is a viable dairy cow feed.
Acknowledgements: Key research collaborators included Mary Raeth-Knight, Hans Jung, Noah Litherland, Jim Linn, and Jim Paulson; University of Minnesota (Extension) and USDA-ARS-St. Paul. Thanks to the Midwest Forage Association and the U.S. Dairy Forage Research Center for their financial support of this research.
Source: University of Minnesota Extension