What is the Dairy Feeding Value of High-Quality Grass Forage?

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1 What is the Dairy Feeding Value of High-Quality Grass Forage? FINAL REPORT to the Midwest Forage Association Board of Directors Submitted 6 January 2011 For a $4500 MFRP Grant (2007) ending 31 October 2009 P.I.: Paul R. Peterson, University of Minnesota Extension Collaborators: Mary Raeth-Knight, Hans Jung, Noah Litherland, Jim Linn, and Jim Paulson; University of Minnesota (Extension) and USDA-ARS-St. Paul KEY FINDINGS: This single feeding trial with 50 UMN-St. Paul Campus Holstein dairy cows indicated that replacing corn and soybean meal with from 10 to 30% orchardgrass hay resulted in similar milk production compared to replacing with alfalfa hay from 15 to 35% of the diet DM. In addition, the orchardgrass hay had a similar rate (average 4.9%/hour) and greater extent (79 vs. 55%) of fiber (NDF) digestion compared to the alfalfa hay. Our objective was to use linear-regression analysis to compare the change in lactating dairy cow performance when increasing amounts of corn grain and soybean meal are replaced with alfalfa or orchardgrass hay in a total mixed ration (TMR). An eight-week feeding trial was conducted in February through March 2009 with thirdcutting (2008) orchardgrass hay from the US Dairy Forage Research Center Farm at Prairie du Sac, WI; it tested 16% CP, 33% ADF, 60% 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 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 included 35% corn silage as well. Diet specifics are in Tables 1 and 2. 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 1

2 decreased from 10 to 6%, as hay inclusion increased from 10 to 30% of diet DM. The TMR diets were fed once daily. Table 1. Ingredient composition of five ALFALFA-based TMR diets for Holstein dairy cows at UMN-St. Paul as influenced by alfalfa-hay inclusion level. Ingredient Alfalfa Hay, % of Diet DM Corn Silage Alfalfa Hay, ground Corn, ground Soybean Meal, 44% Protein/Mineral mix Molasses mix Calcium carbonate Monocalcium phosphate Table 2. Ingredient composition of five ORCHARDGRASS-based TMR diets for Holstein dairy cows at UMN-St. Paul as influenced by orchardgrass-hay inclusion level. Ingredient Orchardgrass Hay, % of Diet DM Corn Silage Orchardgrass, ground Corn, ground Soybean Meal, 44% Protein/Mineral mix Molasses mix Calcium carbonate The 48-hour NDF digestibilities (NDFD) of the hays (measured in vitro via wet chemistry ) were 71% for orchardgrass and 52% for alfalfa (Figure 1). Dry matter intake of the orchardgrass- vs. alfalfa-based TMRs behaved similarly, decreasing ~0.8 lb/cow/day per unit 2

3 increase in hay inclusion from 10 to 35% of diet DM (Figure 2). Milk production (3.5% fatcorrected) also behaved similarly, decreasing ~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 3). A striking difference between the hays was the relationship between milk production and diet-ndf concentration (Figure 4). For the orchardgrass-based TMRs, milk production declined ~1 lb/cow/day per unit increase in total-diet NDF from 30 to 40% DM. For the alfalfabased TMRs, milk production declined ~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- 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. 3

4 Figure 1. Digestion kinetics of alfalfa (A) vs. orchardgrass (OG) hays. In-vitro NDF digestion rates were 5.2 and 4.6 % per hour, respectively, for A vs. OG (statistically similar). Corresponding A vs. OG 48- and 96-hr IVNDF digestibilities were 52 and 55% vs. 71 and 79% of NDF, respectively. 4

5 Figure 2. Lactating dairy-cow dry matter intake (DMI) of alfalfa (A) vs. orchardgrass (OG) hays as influenced by inclusion rate (10-35% of DM) in TMRs. The rate of decline in DMI with increasing forage inclusion was similar for the A and OG hays, averaging ~0.8 lb DMI/head/day per unit increase in forage %. 5

6 Figure 3. Milk yield (3.5% fat-corrected) of Holstein dairy cows consuming alfalfa (A) vs. orchardgrass (OG) hay at 10-35% TMR inclusion rates. The rate of decline in milk production with increased forage inclusion was similar for A vs. OG hays, averaging ~0.6 lb milk/head/day per unit increase in forage %. 6

7 Figure 4. Milk yield (3.5% fat-corrected) of Holstein dairy cows consuming alfalfa (A) vs. orchardgrass (OG) hay as influenced by dietary NDF percentage (% DM). The rates of decline in milk production per unit increase in dietary NDF % were ~2.7 vs ~1.0 lb/head/day per unit increase in diet-ndf % for the A- vs. OG-based TMRs, respectively. 7