In 2014, the USDA reported that 89.4 percent of dairy operations in the U.S. included corn silage lactating cow diet. Dry mater intake potential and, consequently, energy content of dairy cows’ dietary consumption is limited by the amount of fiber present in the forage.
More fibrous corn silage increases the dietary bulk in the rumen of the cow, preventing the cow from eating more – and yielding less milk.
In dairy nutrition, when evaluating the quality of a feedstuff, nutritionists focus on four main quality chemical tests for indication of fiber in the diet as a percentage of the dry matter (percent DM): neutral detergent fiber (NDF), acid detergent fiber (ADF), lignin and neutral detergent fiber digestibility (NDFd, percent of NDF). Ideal forage quality results are low in NDF, lignin and ADF content and high in NDFd.
Researchers from the University of Wisconsin have shown that increasing the NDFd of corn silage by 2 percent allows cows to eat more (11 pounds per day) and produce more milk (13 pounds per day).
For a projection of how a given corn silage will allow the cow to perform in terms of milk yield, nutritionists and producers can opt to have corn silage samples modeled based on the digestibility and energy content of the silage.
Milk pounds per ton of DM (MILK2006) is an index of forage quality developed by researchers at the University of Wisconsin. The projected milk value uses ADF to estimate the energy of the feedstuff and NDF and NDFd used to estimate dry matter intake (DMI).
In addition to evaluating fiber quality, tests can be performed on fresh corn silage samples for an assessment of silage quality and the fermentative environment in the silo.
In a fermentation profile, volatile components of interest include pH, lactic acid and total acid. Lactic acid, a secondary source of energy for rumen microbes, is produced by lactic acid bacteria present in the silo environment – and is the goal of good fermentation.
Greater amount of lactic acid in the corn silage will decrease pH, limiting the development of other micro-organisms that require higher pH to be active. The presence of yeasts and fungi in the ensiled plant material compete with the lactic acid bacteria for sugar substrates, increase the pH and decrease the amount of sugars, also known as water-soluble carbohydrates, available to the cow.
Researchers in Mexico evaluated changes in corn silage fermentation over a 10-month period, measuring lactic acid, pH and mycotoxins, a secondary toxin formed by fungus which can be harmful to dairy and human health.
When lactic acid in the corn silage samples decreased 0.93 percent (6.62 to 5.69 percent, respectively), pH decreased to 0.4 (3.88 to 3.48, respectively), and mycotoxin development in the corn silage significantly increased 3.9 parts per million (1.4 to 5.3 ppm, respectively).
Fungal disease on corn plants, such as northern leaf blight and gray leaf spot, can result in yield losses and decreased quality for animal feed. In 2013, 7.5 percent of the total estimated corn bushels were lost to fungal disease.
When environmental conditions are favorable for fungal disease, such as wet and humid weather, fungal pathogens create lesions on the leaves, reducing the total leaf area available for photosynthesis. When summers are cooler and wetter than normal, like in 2015, fungal lesions develop earlier on the plant.
Increased lignification of the plant cell wall is one of the mechanisms plants use to defend against fungal pathogens. It is hypothesized that the increased lignin content acts as a barrier to protect the rest of the plant from further damage.
Increases in lignin of the cell wall can cause decreases in NDFd and increases in NDF and ADF, affecting dairy diets, especially since corn silage is about 70 percent fiber and 30 percent starch.
Once fungal disease has invaded the plant cells, the pathogen competes with the plant for the starch, non-fibrous carbohydrates and sugars, potentially decreasing the sugar content of the plant.
One of the tools available to producers for control and prevention of fungal disease in corn is to apply fungicides at various stages in corn development. A University of Wisconsin study evaluated the effect of pyraclostrobin foliar fungicide on corn silage quality and yield.
Researchers reported that applications of pyraclostrobin on corn numerically decreased diseased foliage by 5 percent, when compared with untreated, and decreased stalk rot by 16 percent.
Furthermore, pyraclostrobin application on corn significantly reduced NDF by 1 percent (percent of DM) and numerically increased NDFd and starch when compared with untreated.
Using MILK2006, pyraclostrobin application on corn numerically increased projected milk production by 75 pounds milk per ton DM when compared with control.
In 2014, our group at the University of Illinois fed dairy cows one of four different foliar fungicide-treated corn silages, looking at silage quality and in situ digestibility. Corn silages varied in treatment with control and either one, two or three applications of foliar fungicide.
It was determined that applications of fungicide on treated corn decreased fiber content (NDF and ADF) compared with control. Furthermore, as the number of applications of foliar fungicide increased on corn silage, the ADF content decreased.
Applications of foliar fungicide on corn resulted in increased dry matter digestibility when evaluated in situ. Cows receiving diets treated with foliar fungicide had greater feed conversion, which is the amount of feed required to make 1 pound of milk, compared to control – suggesting a higher-energy forage.
From that study, we concluded that applications of fungicide on corn may be positively affecting the corn silage quality when fed to cows. Therefore, in 2015, we sought to answer if applying fungicide on corn would have an effect on the nutrients once ensiled and the most efficacious time of application for silage production.
All corn was harvested on the same day in mid-corn reproductive stage four (R4, when starch in the kernel is thickening into a pasty consistency). Samples of corn silage from each of the four treatments were packed in mini-silos to replicate the effects of fermentation on the treatment corn silage.
Treated corn silage was ensiled for one of four allotted lengths of time: zero days post-harvest, 30 days post-harvest, 90 days post-harvest and 150 days post-harvest. Results for the treatment effect – which affected the DM, lignin, water-soluble carbohydrates, milk pounds per ton of DM, lactic acid and total acid of foliar fungicide application on corn silage – are shown in Table 1.
Additionally, we analyzed the effects of fungicide treatment on corn silages ensiled for different lengths of time post-harvest. Corn silage from corn that received fungicide application at R1 had greater lactic acid over the four various lengths in-silo when compared with other treatments (Figure 1).
Fungicide application on corn seems to alter the fiber content within the plant material and fermentation products of corn silage. Frequent scouting in the cornfield and awareness of changing weather conditions are crucial in helping to limit fungal development on corn.
Applications of fungicide on corn can prevent fungal disease in the field, which may decrease the amount of fungal pathogens ensiled in corn silage. Preventing disease on corn early may decrease NDF and ADF content. Ideally, decreasing NDF, ADF and lignin content of corn plants may increase NDFd of corn silage when fed to dairy cows.
Furthermore, ensiling corn silage with less fungal pathogens may increase lactic acid content of the silage. By increasing ruminal digestibility and increasing the fermentative quality of corn silage, diets may increase feed conversion of feed to milk, making dairy production more efficient. PD
For more information on foliar treatments and rates used, contact the authors.
Phil Cardoso is an assistant professor in the University of Illinois Department of Animal Sciences. Email Phil Cardoso.
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PHOTO: Chopping corn. Photo by Walt Cooley.