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Surface and core temperature measurements of your forage – What do they tell you?

John Goeser and Chris Hallada Published on 16 September 2010

Harvesting, storing and feeding high-quality forages can help your dairy survive a challenging dairy economy by increasing your margin of milk income over feed cost. If nature is forgiving and highly digestible crops are chopped, the next daunting task at hand is fermenting, storing and feeding with a minimal loss of nutrients.

Feeding high-quality forage makes more milk, but what does forage temperature have to do with several pounds more milk? We’ll take a look at two forage temperature measures – surface and core – to find the answer.



Let’s start by discussing what happens when your silo is sealed. An explosion of microbial growth occurs during the initial days of ensiling, together with a rise in silage temperature. Few people know that the outside temperature during harvest dictates the internal forage temperature in your silo.

If air temperature is 90°F when harvesting, your silo will likely be 90°F or higher and can retain that heat for a long time, particularly in large silage masses. Air temperature rises during wilting, and filling losses increase due to plant respiration. Mother Nature controls the average temperatures outside, so we can do little to avoid these losses.

We mentioned a subsequent rise in forage temperature during initial fermentation. We use a benchmark of 20°F higher than outside temperature at harvest as an acceptable maximum core fermentation temperature. The core temperature measure is taken at 18 inches of depth from the feedout face toward the center of the silo face. Management practices such as filling quickly; inoculating with proven bacteria; and optimizing chop length, moisture, packing and sealing the crop, will all help limit the maximum fermentation temperature and preserve digestible nutrients.

The wide variations in temperature have often been ignored in the field until recently. Italian scientists Borreani and Tobacco discovered that any forage with temperatures roughly 10°F higher than core temperatures had higher yeast and mold counts. Thus, the researchers suggested temperature measures can indicate forage quality status. Dr. Limin Kung of the University of Delaware has suggested that forage temperatures above 95°F can cause protein damage. In the field, we’ve observed 10 percent damaged protein in several alfalfa haylages. This 10 percent damage was estimated at 35 pounds of protein per ton of forage. Less-usable protein can equate to less microbial protein and lower milk production potential. We don’t yet have field core temperature benchmarks or know what percentage of (or when) field silos have core temperatures at 95°F or above. However, we’ve observed core measures of 130°F or higher in some seemingly well-managed bunkers and piles. Look for more research and information in the coming months and years as we learn more about on-farm silo core temperatures and how to use them.

Other serious nutrient burglars are yeast, mold and other aerobic organisms that grow as forage is re-exposed to air. In recent years our bunkers, bags and piles have gotten bigger. Larger surface areas of these silos covered with plastic and tires create plenty of opportunity for oxygen to infiltrate by billowing under the plastic, through punctures and along imperfectly covered seams or edges. Likewise, as bunkers and piles have gotten larger, so have the open surfaces exposed at feedout. It is now common for a 50-foot wide by 15-foot tall face to be exposed – nearly a quarter of the size of a basketball court.


Once a silo is opened, microorganisms that were dormant in the absence of oxygen may multiply quickly, particularly if the forage pH is high (4 to 4.5). This is usually characterized by a dramatic increase in yeast numbers, followed by visual mold growth. The best-managed silos have 5 to 10 percent shrink due to fermentation and feeding losses. Oxygen infiltration due to inadequate sealing and feedout practices can cause losses of another 10 percent or more. For example, if your silo inventory is 1,000 tons, the additional losses could be 100 tons. That’s 3 to 6 acres of corn silage or 5 to 15 acres of alfalfa.

Aside from additional shrink, which might amount to thousands of dollars, animals consuming deteriorated silage can result in digestive upsets, lower energy and nutrient intake, decreased milk production or even clinical disease, such as hemorrhagic bowel syndrome. Forage surface temperature measures can help determine if you’ve got a real problem on your hands.

Several groups have begun using thermal imaging cameras (infrared) in the past few years to “see” surface heat and spoilage that the naked eye cannot. These cameras provide detailed surface temperature information and may change how we manage forage.

For example, we all understand that mold on silage should be removed prior to feeding. Using the thermal camera, we can “see” deterioration in an area three times the size of the visibly moldy feed. In reality, all of this feed should be disposed of to avoid putting our animals at risk, not just the visually moldy forage. Many factors aside from aerobic deterioration also impact surface temperature measurements, including sun exposure, ambient temperature and moisture. Thus, experience with forages and the camera is a must so that the pictures are not misinterpreted. We have found the camera settings are also critical to getting accurate measures. When diagnosing surface problem areas with your consultant and the infrared camera, look for unnatural changes in temperature on the thermal image and surface temperature ranges of 20°F or higher.

Forage temperature probes can also do the job if an infrared camera is not available. Surface measures in the outer 6 inches at 15 to 20 equally spaced spots across the face width can show you problem areas. With the probe, look for changes in temperature of 10°F or more from the core temperature (greater than 18 inches deep) before considering management alternatives.

In summary, bunker, pile and bag surface and core temperature measures may seem like an overly simplistic quality analysis, but research is beginning to show us relationships between temperature measures, yeast and mold counts, and feed deterioration. Higher yeast and mold counts, dry matter losses and protein losses impact your bottom line by decreasing feed quality and milk, so consider using this approach once or twice a year to look for the next opportunity to improve. PD


References omitted due to space but are available upon request by sending an email to .

John Goeser