Editor’s note: This article was written by Paul R. Peterson, Forage Agronomist with the University of Minnesota Extension.
Good quality grass hay can be a valuable feed for high producing dairy cows. In a recent feeding trial with 50 Holstein dairy cows at the University of Minnesota-St. Paul Campus, replacing corn and soybean meal with rates from 10 to 30 percent orchardgrass hay resulted in similar milk production compared to replacing them with alfalfa hay from rates of 15 to 35 percent of the diet dry matter (DM).
The eight-week feeding trial was conducted February through March 2009 with third cutting (2008) orchardgrass hay from the U.S. Dairy Forage Research Center Farm at Prairie du Sac, Wisc. It tested 16 percent crude protein (CP), 33 percent acid detergent fiber (ADF), 60 percent neutral detergent fiber (NDF), and 2.4 percent lignin. These test results were based on the average of weekly grab samples of chopped hay. For context, this might be considered 'good' but not 'great' quality grass hay. The alfalfa hay being compared in the trial tested 22 percent CP, 31 percent ADF, 41 percent NDF, and 4.7 percent lignin. Both hays were ground in a vertical mixer prior to feeding; five minutes for alfalfa and 30 minutes for orchardgrass.
The feeding trial had 10 treatments including alfalfa hay fed at 15, 20, 25, 30, and 35 percent of diet DM; vs. orchardgrass hay fed at 10, 15, 20, 25, and 30 percent of diet DM. These variable hay types/amounts replaced corn grain and soybean meal in TMRs that also included 35 percent corn silage.
For alfalfa-based TMRs, ground corn was decreased from 21 to 8 percent and soybean meal decreased from 7 to 0 percent as hay inclusion increased from 15 to 35 percent of diet DM. For orchardgrass-based TMRs, ground corn was decreased from 21 to 6 percent and soybean meal decreased from 10 to 6 percent as hay inclusion increased from 10 to 30 percent of diet DM. The TMR diets were fed once daily.
The 48-hour NDF digestibilities (NDFD) of the hays (measured 'in vitro' via 'wet chemistry') were 71 percent for orchardgrass and 52 percent for alfalfa. In addition, the orchardgrass hay had a similar rate (average 4.9 percent per hour) and greater extent (79 vs. 55 percent) of fiber (NDF) digestion compared to the alfalfa hay. Dry matter intake of the orchardgrass- vs. alfalfa-based TMRs behaved similarly, decreasing approximately 0.8 lb/cow/day per unit increase in hay inclusion from 10 to 35 percent of diet DM. Milk production (3.5 percent fat corrected) also behaved similarly, decreasing approximately 0.6 lb/cow/day per unit increase in hay inclusion percentage from 10 (98 lb/day) to 35 percent (82 lb/day) of the diet DM (Figure 1).
Figure 1. Milk yield (3.5 percent fat corrected) of Holstein
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