From hay to neigh: How rain can affect the quality of hay

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A farmer inspects the quality of his hay. Photo: File
A farmer inspects the quality of his hay. Photo: File

Is rained-on hay any good for our equine friends? Many horse owners have to make this judgment call, when they consider the effects of rain.

The hay-making season in the northern hemisphere has been under way in many places for several weeks. Some parts of the globe enjoy gloriously settled conditions at this time of the year, whereas other areas experience unpredictable weather.

Rain during haymaking raises an important question: what happens to the quality of the end product?

Jimmy Henning, an extension professor in the Department of Plant and Soil Sciences at the University of Kentucky, says most damage from untimely rain is the loss of soluble nutrients from the hay (the sugars).

“Even before rain damage, we lose some sugar during plant respiration that occurs from the time forage is cut until it reaches about 50% moisture content,” Henning writes in the latest issue of the Equine Science Review.

Rainfall will extend the length of time that the hay is wetter than 50% moisture, leading to more loss of sugars from respiration.

Rainfall also leaches the soluble sugars from hay, he explains.

The amount of leaching depends on the forage type, the hay moisture content when it rains, the concentration of soluble sugars and the number, amount and intensity of rainfall events.

Leaf shatter can also be significant in legumes, especially on nearly dry forage.

Hay that has been rained on during curing will also have greater levels of dirt as well as higher numbers of microorganisms that will cause molding in the bale.

Finally, the extra tedding and raking that may be needed to cure the crop can lead to further losses, especially in legume hay.

IVDMD refers to In vitro dry matter digestibility. %DM refers to percent of dry matter.

Research done by Mike Collins, a retired University of Kentucky forage scientist, provides some insight into the question of how much quality is lost due to rain.

Collins measured the digestibility of alfalfa hay and red clover forage which experienced rain at different times after cutting.

In the 1980 research, 1 inch of rain that fell soon after cutting had little negative impact on forage digestibility.

In a second study, 1.6 inches of rain during curing (after some drying had occurred) caused significant losses in digestibility.

Getting 2.4 more inches of rain on almost dry hay caused further damage, truly making some of the forage of little value (for example, 36% digestibility in rain-damaged late-bloom alfalfa).

With severely rain-damaged hay, it may better to leave it on the field, chop it up with a rotary mower to speed decomposition and minimize shading of the next crop, Henning says.

Similar research at the University of Arkansas found dry matter losses were below 2% for second cutting orchardgrass with up to 3 inches of simulated rainfall when the forage was at 67.4% moisture (that’s the moisture level just after cutting).

Dry matter losses quadrupled to 8% when the same amount of water fell on forage at 15.3% moisture (the moisture level desired for making dry hay).

In the end, deciding what to do with rain-damaged hay is a judgment call, Henning says. Many factors come into play such as when the rainfall occurs during curing, the amount and intensity and how dry the crop was when rained on.

“I find it helpful to know that rain immediately after cutting can do minimal damage,” he says.

This report first appeared in the June issue of Farmer’s Pride.

Article courtesy University of Kentucky College of Agriculture, Food and Environment.

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