There are a number of reasons why cows reject hay. In some cases, it just isn’t very good hay.
Dr. Shane Gadberry, professor of animal science with University of Arkansas Extension, said cattle may reject hay because of its low digestibility. That could be caused by “the fact that hay was just harvested too mature,” Gadberry told Ozarks Farm & Neighbor. “It’s more fibrous; it takes longer for the rumen microbes to get in there and break down that fiber. So that basically slows the rate of digestion and if we have a slower rate of digestion, we have a reduction in intake.”
Hay can also be less digestible because it’s deficient in protein. Gadberry said it’s preferable to have the TDN (total digestible nutrient) to protein ratio in the range of 4:1 to 6:1. “In some instances, if we have neglected good fertilization practices according to soil tests, we may have hays that have very low protein content,” he said. The microbes in the animal’s rumen may not be adequate to fully utilize the hay; the situation can be remedied with supplemental protein, to bring protein and energy into better balance. Rejection of hay due to quality problems leads to both reduced performance and wasted feed, as cows will sort through the hay, searching for parts that are more palatable and digestible.”
When hay is put up too wet, it enhances the likelihood of mold. Cattle appear to be less susceptible to mold than horses and most molds are not harmful to the cattle, but some secrete mycotoxins that can cause mycotic abortion, respiratory disease or aspergillosis, which is caused by several molds in the same family as Aspergillus flavus, the cause of aflatoxin in grain. It may take days or weeks for symptoms from these infections to appear; often, the cows will reduce their dry matter intake. This could be followed by diarrhea and by signs of ketosis or hemorrhaging. Another potentially problematic mycotoxin is zearalenone, which is produced by several Fusarium fungal species on grains and can ultimately affect reproduction rates in cattle.
The appearance of other fungi in stored forage can contribute to rejection, according to Eldon Cole, livestock specialist with University of Missouri Extension. The presence of ergovaline, which is found in endophyte infected fescue, can put cows off their feed, although the longer the fescue has been put up, the more the toxin level declines. Yet another fungus, Rhizoctonia leguminicola, causes a disease known as “black patch” in red clover; cattle turn away from the infested legume, which can cause animals to slobber and exhibit other symptoms.
Even if a mold isn’t harmful, it could change the taste of the hay and cause cattle to reject it for that reason. Gadberry said because so many molds are harmless to cattle, a mold count doesn’t provide a substantial amount of useful information. You also have the opposite situation of rejection when wet hay starts to ferment; there are reports that cattle prefer the taste of that hay, but the heat produced by fermentation makes some of the protein in the hay unavailable to the animal. Cole recommended subjecting the hay to a standard protein test, to determine whether it needs to be supplemented.
If cattle are rejecting hay, can it just be replaced? “That’s easier said than done,” said Gadsberry. “We’ve invested money in that hay and would like to be able to utilize it.” If the problem is mold, there are several labs that can evaluate it; if the cows aren’t eating it for another reason, it could be made more palatable. Some producers add liquid feed supplements to hay, in some cases using specialized equipment to inject it into the bale. Or, said, Gadsberry, you can alternate hay feedings, giving the cows feed they prefer part of the time, and reducing the negative impact on performance.


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