By Margaret Smith, PhD
Albert Lea Seed Agronomist

It’s been a summer to remember—but not with fond memories if you were making hay! Rain in July in much of the Upper Midwest was far above average. Most growers got their first cut of hay baled in good time, but due to frequent rains and high humidity, the second and thirds cuts were extremely challenging to get up and with good quality. 

In Albert Lea, Minnesota, we received only 2.36” of rain in May, then 6.20” in June, and 8.33” in July. Rainfall varied wildly across weather sites just in Freeborn County (home of Albert Lea). Across the county, rainfall across all weather sites ranged from 4.68” to 10.52” in June and 5.17” to 12.65” in July. Farmers and other weather watchers know that the high variability in rain frequency and amounts was typical of the entire Upper Midwest and Corn Belt. Relative humidity was also high through much of July—in part, fueled by all the rain.  

Rains delayed many second hay cuttings and, after cutting, much of that hay was rained on in the windrow. Hay and haylage made during this period may be of limited feed value and questionable quality. Animals may refuse this poor quality feed simply because it’s different than what you have been feeding. If low protein and digestibility are the only issues, you can mix it with higher quality forage and ‘sweeten the deal’ with molasses to get your animals started eating it. Dusty hay may be accepted, but is a particularly a poor choice to feed to horses, because it can cause heaves. Many farmers took the precaution this year of treating dry hay with a preservative to prevent molding, but preservative aren’t always adequate to prevent further deterioration in storage.  

Farmers have reported problems with some second-cut hay with both reduced feed quality, but also with mold. We recommend testing damaged or poor quality hay before feeding. Certainly, test for feed quality so that you can adjust your feed rations as needed, but also for anti-quality factors, including molds and mycotoxins. 

Hay Samples Analyses from the Upper Midwest

Second-cut hay and haylage samples from two farms in the Upper Midwest were analyzed for feed quality (Table 1). Both farms are growing alfalfa/grass mixes. The second cutting on the beef farm was delayed and hay was rained on in the windrow. Preservative was applied when baling, but the moisture level of 21% can still allow mold growth in the bales. Surprising protein levels and NDF percent indicate better hay than expected (Table 1), but animals in the feedlot wouldn’t touch it! Further analysis measured mold levels of 200,000 spores per cm of hay. Animal refusal may have been from these molds or from the hay preservative recently applied. 

Cutting was also delayed on the dairy farm for this haylage (Table 1). Quality is poor for lactating cows, but it can be blended or used for dry cows or developing heifers. No molds were detected.  

Table 1. Forage analyses for second-cutting hay and haylage on two farms in the Upper Midwest, 2025  

*Relative Feed Value (most appropriate for straight alfalfa forage stands)
**Relative Feed Quality (better measure for mixed legume/grass or straight grass forages)

Feeding Moldy Hay

Mold spores have a negative effect on forage palatability, acceptance, and digestibility and can reduce animal performance by 5 to 10%. Symptoms associated with feeding moldy hay may include feed refusal, allergy symptoms similar to asthma (e.g. heaves), reduced feed intake, poor weight gain, colic in horses, diarrhea, lower fertility, poor kidney or liver function or abortions. Horses are most susceptible to molds, but cattle and sheep may also exhibit these symptoms. In addition, mold can induce farmers’ lung in farmers who breathe in the spores while feeding hay. Having experienced this issue, I highly recommend wearing a dust mask (capable of excluding 5-10 micron particles) if you do feed any moldy hay—even at low infestation levels. 

Pennsylvania State University offers the following guidelines for feeding moldy hay (Table 2). These risks and guidelines are considered WITHOUT mycotoxins produced by the molds, so reflects risks from molds, only. 

Table 2. Feeding Risks* at Various Mold Spore Counts 

*Risks refer primarily to effect of mold without regard to possible mycotoxin content. Dust may also reduce feed consumption.
Data from Richard S. Adams, Kenneth B. Kephart, Virginia A. Ishler, Lawrence J. Hutchinson, and Gregory W. Roth. 1993. Mold and mycotoxin problems in livestock feeding. The Pennsylvania State University.

Visible mold on this hay indicates to use caution when feeding it. A lab test will help inform how much you need to dilute or mix this hay in rations.

Mycotoxins in Moldy Hay

There may be double trouble with moldy hay if the molds produced toxins. The most likely mycotoxins to be produced from forage molds are aflatoxin and fumonisin, but there may be others present, as well. Mycotoxins in dry hay are most serious for horses, as their digestive system can’t break them down. (Hogs and poultry also can’t detoxify mycotoxins, though those of concern are from infected grains in their rations rather than forages.)

Low levels of mycotoxins are degraded in the rumen of cattle and sheep, but secondary metabolites of that degradation can affect animal health and performance. But, mycotoxins at high levels can overcome the rumen’s ability to full detoxify them. In addition, ruminants are less able to detoxify fumonisin than other mycotoxins, so identification of both mycotoxin type and the level is important.  

Ask your testing lab which toxins they can screen for. If you receive positive tests, consult your veterinarian and feed ration consultant to help develop a feeding strategy. 

Laboratory Testing for Molds and Mycotoxins

Ask your preferred lab if they test for molds. Most forage testing labs will test for molds (forage mold analysis is about $38 per sample, with results reported in spores per gram of feed), but not all test for mycotoxins. If not, a list of Forage Testing Laboratories certified by the National Forage Testing Association (NFTA) is available on the NFTA website.

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Resources:

• Association Between Forage Mycotoxins and Liver Disease in Horses, National Library of Medicine
• Dairyland Laboratories, Inc.     
• Information on Farmer’s Lung, Cleveland Clinic   
• Hay, Molds, and Feeding Problems in Montana, Montana State University 
• Freeborn 2025 Monthly Precipitation Totals, Minnesota State Climatology Office
• Mold and Mycotoxins in Horse Hay, Penn State
• Mycotoxins in Feed, Penn State 
• National Forage Testing Association  
• Anti-Nutritional Measures, Rock River Laboratory, Inc.
• Toxin Degradation by Rumen Microorganisms: A Review, National Library of Medicine