Flood damaged forage may have elevated levels of ash and/or bacterial contamination. Both must be considered when feeding this forage to animals.
Internal mineral content of forages is usually 6 to 8% and forage normally has 2 to 4% soil contamination to give a total of 10 to 12% ash (see table). The soil contamination is largely silica and of no nutritional value to animals. This means that forage fed to animals should be increased when ash levels above are 10 to 12% and the value of forage reduced correspondingly.
Horses can be particularly sensitive to high ash content in the hay as the silica buildings up in the intestinal tract of the horse and causes Sand Colic. The sand/silica causes pain by two methods: 1) Sand presses on the bottom of the intestine, preventing blood from entering the area. This causes the long term, low grade pain that can cause a horse to eat poorly without ever really acting colicky. 2) Eventually sand can build up to the point that it totally blocks a loop of intestine. This causes a very painful buildup of hay and water in front of the blockage. Once pressure builds to a certain point, it either pushes out the sand blockage or pops the intestine like an overfilled balloon. Intestinal rupture is always fatal.
A second major problem caused by flooding is that bacteria and other microorganisms may have contaminated the forage, especially if flood water flowed across manure piles or city sewage facilities or include runoff from manured land. Flood water may contain Escherichia coli and Campylobacter jejuni which can cause illness and death in both humans and animals. Other manure-borne pathogens can be present, including Giardia lamblia and Cryptosporidium parvum. Additionally manure-borne protozoan parasites are infectious at very low doses and may be able to survive in manure and surface water for long periods.
Bacteria and fungi may grow and produce mycotoxins on alfalfa /grass lying in the field. This is less of a problem on corn harvested for silage than for alfalfa or grass fields due to openness of the corn plant and reduced microbial growth. This microbial growth may be less of a problem if harvested forage is fermented because the associated heat will reduce microbes; though forage may still contain mycotoxins. Cattle can tolerate higher microbial populations than sheep, horses, and other animals.
Source:uwex.edu