Akins is a dairy scientist at the U.S. Dairy Forage Research Center in Marshfield, Wis. Gumus is a visiting scientist with the University of Wisconsin-Madison.
As dairy producers have been growing more corn silage and feeding it in lactating cow rations, there has also been a rise in the use of other annual forages. This has been driven by expanding interest in planting cereal grains after corn silage is chopped and harvesting forage the following spring.
The use of various annual forages are also becoming common after the cereal grain forage harvest. One popular option is to use annual forage mixtures that contain cool-season (Italian ryegrass) and/or warm-season (brown midrib sorghum-sudangrass) annual grasses and legumes such as clovers and hairy vetch. Often these are called “cocktail” forage mixes.
The grass type included in the mix is likely the most important consideration and depends on the soil conditions and manure management. Sorghum-sudangrass does not tolerate wet soils or can be damaged by in-season manure applications; however, Italian ryegrass will not tolerate dry soil conditions, so the two are sometimes mixed to provide some insurance for what Mother Nature may provide.
In our work with cocktail mixes in 2021 and 2022, we have focused on a mix with sorghum-sudangrass, Italian ryegrass, and legumes. As part of a project funded by the University of Wisconsin Dairy Innovation Hub, we evaluated on a field-scale the yield and quality of cocktail forage mixes on four farms, including the University of Wisconsin’s Marshfield Agricultural Research Station. Those results are in the March 2022 issue of Hay & Forage Grower.
Forage quality differed
The project also included feeding the forage from the second harvest, as it contained a blend of the two grasses, while the first harvest was primarily sorghum-sudangrass and the third harvest was primarily ryegrass. We harvested the forage in mid-September with cutting and wilting for one day and then chopping for silage. The silage was allowed to ferment for four weeks before feeding. Ideally, the silage would have been allowed to ferment longer as it was not yet stable and had aerobic stability issues (yeast growth) due to a slow feedout rate during the study.
The diets included a mixture of corn silage (29% of diet dry matter [DM]) and either an alfalfa-grass silage or the cocktail mix silage (18% of diet DM) in addition to concentrate ingredients (Table 1). The treatment rations were fed to 16 first-lactation cows that were on each diet for eight weeks. The cocktail mix silage was higher in fiber (51.6% neutral detergent fiber [NDFom]), but the fiber was much more digestible (68% NDFD30) compared to the alfalfa-grass silage (40.4% NDFom; 52.2% NDFD30). Soybean meal was used to help balance protein since the cocktail mix silage was lower in protein content.
Diet nutrients mainly differed in starch and fiber with the cocktail mix diet having less starch (26.8% starch) and more fiber (26.2% NDFom) than the control diet (28.4% starch; 22.3% NDFom). The NDFD30 of the cocktail mix diet was higher (68% of NDF) than the control (61.9% of NDF), which helped make the diets more similar in energy.
The cows on each diet ate similar amounts of feed (57.2 pounds of DM), with the cows fed the cocktail mix diet eating more NDF (14.9 pounds of NDF) than the control diet (12.8 pounds of NDF), so fiber level did not result in reduced intakes, which was likely due to the fiber levels being fairly low (22% to 26% NDF). As mentioned earlier, the cocktail mix silage had poor stability after opening due to a slow feedout rate, and the farm staff discarded spoiled silage to reduce the effects on intakes. Feed intakes for both treatment diets increased during the study, so the impact was likely minimal.
Milk and components offset
Looking at milk production, cows fed the control diet produced more milk (83.7 versus 81.4 pounds per day). However, milk components were higher for cows fed the cocktail mix diet, with higher milk protein (3.45% versus 3.38% protein) and slightly higher milkfat (4.83% versus 4.74% fat). When considering both milk yield and components, the energy-corrected milk yields were similar between diets (89.2 pounds per day for the control and 88.2 pounds per day for the cocktail). The difference in components also resulted in similar fat and protein yields for cows fed either diet.
Total-tract digestibility of NDF was similar to in vitro estimates with the cocktail mix diet having 66.2% NDFD and the control diet having 63.8% NDFD. However, dry matter and starch digestibility were greater for the control diet (81.5% DM and 99.2% starch digestibilities) than the cocktail mix diet (78.7% DM and 98.7% starch digestibilities).
Interestingly, when we measured the greenhouse gas emissions from the cows’ eructated gases, the cows fed the cocktail mix diet released about 9% less methane (411 grams of methane [g CH4] per day) than the control diet (450 g CH4 per day). The reason for the reduction in methane released is potentially due to lower overall diet digestibility; however, methane typically comes from fiber fermentation and the cocktail mix diet had higher fiber levels. This was an unexpected outcome, so the specific reason for differences in methane emission needs further investigation.
Account for variability
The take-home message from this study is that cocktail forage mixes can be used in lactating cow diets as a substitute for other hay-crop silages. Ration formulation should consider differences in protein, NDF, and NDF digestibility between the forages to maintain similar protein and energy intakes. Based on this work, having a forage with higher fiber digestibility helped offset the difference in energy content due to higher fiber content and maintained similar milk component yields.
With the use of new or different forages, sampling for nutrient analysis and working with a nutritionist is crucial for proper balancing of diets. That’s because the nutrient contents will be different depending on the forage types, fertility, and especially between harvests of cocktail forage mixes.
This article appeared in the March 2023 issue of Hay & Forage Grower on page 20-21.
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