Grass hay makes milk too
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% orchardgrass hay resulted in similar milk production compared to replacing them with alfalfa hay from rates of 15 to 35% 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, WI. It tested 16% crude protein (CP), 33% acid detergent fiber (ADF), 60% neutral detergent fiber (NDF), and 2.4% 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% CP, 31% ADF, 41% NDF, and 4.7% 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% of diet DM; vs. orchardgrass hay fed at 10, 15, 20, 25, and 30% of diet DM. These variable hay types/amounts replaced corn grain and soybean meal in TMRs that also included 35% corn silage.
For alfalfa-based TMRs, ground corn was decreased from 21 to 8% and soybean meal decreased from 7 to 0% as hay inclusion increased from 15 to 35% of diet DM. For orchardgrass-based TMRs, ground corn was decreased from 21 to 6% and soybean meal decreased from 10 to 6% as hay inclusion increased from 10 to 30% 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% for orchardgrass and 52% for alfalfa. In addition, the orchardgrass hay had a similar rate (average 4.9% per hour) and greater extent (79 vs. 55%) 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% of diet DM. Milk production (3.5% 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% (82 lb/day) of the diet DM (Figure 1).
Figure 1. Milk yield (3.5% fat corrected) of Holstein dairy cows consuming alfalfa vs. orchardgrass hay at 10-35% TMR inclusion rates.
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 lb/cow/day per unit increase in total diet NDF from 30 to 40% DM. For the alfalfa-based TMRs, milk production declined approximately 2.7 lb/cow/day per unit increase in total diet NDF from 29 to 36% DM. Note, however, that alfalfa's greater rate of decline in milk production was due largely to substantially lower production at 35% alfalfa vs. all lesser alfalfa inclusion levels.
Milk composition and body weight were unaffected by hay type and amount; averaging 3.8% milk fat, 3.0% milk protein, 4.7% 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.
Dr. Neal Martin Headlines Feb. 8-10 MN Forage Meetings
Former University of Minnesota Extension Forage Agronomist and current Director of the U.S. Dairy Forage Research Center, Dr. Neil Martin will be the featured speaker at forage educational meetings in Cromwell, Feb. 8; Avon, Feb. 9; and Rochester, Feb. 10. The meetings start with registration at 9:30, include lunch, and adjourn at 3:00. Current University of Minnesota Extension Forage Agronomist Dr. Paul Peterson will also speak at these meetings in addition to other University of Minnesota staff. These 'Tour de Forage' meetings are a collaborative effort among the Midwest Forage Association MFA), its local councils, and University of Minnesota Extension. Contact the MFA office at 651-484-3888 or visit midwestforage.org for more information.
Published in Dairy Star January 21, 2011