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Drought
and Feed Poisoning in Dairy Cattle - Part 2
Silo Gas Poisoning.
Silo gas poisoning stems largely from elevated nitrate levels in
ensiled forages. Under some conditions large amounts of nitrogen
oxide gases may be released during ensiling. These are very toxic
to animals, birds and humans. Abnormal or incomplete fermentation
appears to produce more of these dangerous gases. In some cases
it is present only for a few weeks after ensiling, but it may continue
indefinitely in others.
Inhalation
of even small amounts of silo gas may cause choking, asthmatic symptoms
and burning sensations in the nostrils, throat and chest. Deaths
may occur quickly with greater amounts of gas. Severe lung damage
may be present in survivors. A sensitivity to the gas may develop.
Cows subjected to appreciable levels of nitrogen oxide gases may
cough and choke.
Sometimes silo
gas has a yellowish-brown color. This does not always occur. Frequently
it has an odor similar to laundry bleach. It is heavier than air.
This means it may accumulate on the silage surface or flow down
silo chutes and accumulate in low places. Dead birds and small animals
near the silo may be evidence of this problem.
Treatment of
silo gas cases includes drugs to increase aeration and remove fluids
which may accumulate in the lungs. Absolute bed rest and general
supportive treatment are helpful.
Silo gas formation
may be kept to a minimum by ensiling at moisture levels of 60-70
percent to encourage normal fermentation. Also, 8 pounds of sodium
metabisulfite may be added per ton of material ensiled. Most important,
ventilate silos, silo rooms and barns if suspected forage is ensiled.
Don't enter silos for at 7-21 days after filling with suspected
forage. Run blowers for 10-15 minutes before entering. Consult your
medical doctor and/or veterinarian, depending on the problem encountered.
Prussic Acid
Poisoning. This problem is restricted to the use of sorghum, sudangrass
and their crosses. It may result when these crops are used at a
too immature stage or are severely stressed by weather, such as
drought or frost.
Symptoms of
prussic acid poisoning are very similar to those of nitrate poisoning.
It is very important to differentially diagnose the form of poisoning.
Blood drawn from animals suffering from prussic acid or hydrocyanic
acid poisoning may turn brilliant or cherry red upon exposure to
air. In contrast, blood from nitrate poisoning cases may be normal
or chocolate brown in color as drawn.
Acute toxicity
from prussic acid may result in lack of coordination and convulsions
followed by quick death. Treatment with sodium thiosulfate-sodium
nitrite solution is recommended. Repeat treatments with sodium thiosulfate
if necessary.
Ensiling does
not always alleviate the danger of prussic acid poisoning, but levels
generally decline, after about four weeks of ensiling. Drought stricken
forage at any height may be more apt to result in prussic acid poisoning.
Use as pasture, green-chop or hay is more risky than ensiling. Use
suspected material as only part of the ration and heed the other
general recommendations on reducing risk of poisoning. Do not feed
it to hungry animals.
Mycotoxin or
Mold Poisoning. Some feeds or forages may contain highly toxic substances
produced by mold. Material with relatively small amounts of mold
may contain these poisons. They are more likely to be present in
corn and small grains than forage. However, they have been found
in some haylages, silages, ensiled grains and hays. Mycotoxins may
be produced on some feeds before they are even harvested. Others
may be formed during storage.
One of the
most common types of mold poison is aflatoxin. Cattle afflicted
with aflatoxin may have a black or bloody diarrhea from digestive
tract bleeding. Some are uncoordinated and may go down with a posterior
paralysis at any stage of lactation. This problem may not yield
to milk fever treatment. Liver damage frequently occurs. Subclinical
mycotoxicity may result in lower milk production. Another mycotoxin,
zearalenone (DON), may result in swollen vulvas and abortions.
A mycotyoxin
screening test is available from the NDSU Veterinary Diagnostic
Laboratory for $75. Feeds with over 10 ppb should not be sold. Zearalenone
levels of 1 to 5 ppm in feeds may result in reproductive problems.
Reduced appetite may be noted with only .25 to .75 ppm zearalenone
present. Little or no mycotoxins may be formed in silage during
storage if pH falls below 5.0 soon after ensiling.
Other Health
Problems. Enterotoxemia, botulism and listerellosis are more apt
to occur when crops are flooded or silages fail to develop a pH
of under 4.8-5.0. The latter also is true of mycotoxins. The most
frequent causes of elevated pH in ensiled materials are excessive
addition of urea, anhydrous ammonia or other NPN sources at ensiling
and harvesting too dry. Leaking silos and faulty ensiling procedures
also may contribute to fermentation failure.
Hypomagnesemia
or tetany may occur when cattle are eating small grain pasture in
the fall or winter and grasses in spring. Animals may suddenly be
found dead or seen in convulsions or tetany. Make certain that cattle
on such forage are force fed at least 1-2 ounces of magnesium oxide
per head per day.
More problems
with infections, reproduction and metabolic disorders may result
if cows are fed limited forage, high concentrate rations for an
extended period. Feeding corn silage with little or no other forage
may aggravate the problem. Avoid limited forage, high grain rations
for dry cows and springing heifers.
Poisonous weed
problems may also be more prevalent in drought seasons. Ensiling
often does not destroy the toxic substances in many poisonous weeds.
At lower concentrations they may merely reduce appetite, while at
high levels they may result in acute symptoms and death.
An increased
incidence of displaced abomasum or twisted stomach may occur when
either an acidosis or alkalosis occurs in the rumen. An acidosis
is more likely to happen on a high concentrate feeding program,
especially when starchy grains are the major energy source and corn
silage is fed heavily. Highly acid water with a pH under 5.5 may
contribute to the problem. An alkalosis is more apt to occur when
excessive amounts of protein and calcium are fed. This is most likely
to happen on a ration which contains a lot of good alfalfa as hay
or haylage. Highly alkaline water with a pH over 8.5 may also be
a contributing factor. Lack of particle size in the forage portion
of the ration may also result in more DA's. The pH of rumen contents
in most cows should be in the range of 6.7-7.3 when samples are
tested immediately at cow side. Sometimes rumen pH may be as low
as 6.3-6.4 in normal high producing cows fed considerable amounts
of concentrate.
A milkfat test
that runs more than 0.3-0.4 percent from breed average often indicates
that cows are abnormal metabolically. Steps should be taken to alleviate
the problem to prevent possible adverse effects on health and reproduction.
Back
to Drought and Feed Poisoning in Dairy Cattle - Part 1
DS-16-97, June 1997, Reviewed May 2004
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NDSU Extension
Service, North Dakota State University of Agriculture and Applied
Science, and U.S. Department of Agriculture cooperating. Sharon
D. Anderson, Director, Fargo, North Dakota. Distributed in furtherance
of the Acts of Congress of May 8 and June 30, 1914. We offer our
programs and facilities to all persons regardless of race, color,
national origin, religion, sex, disability, age, Vietnam era veterans
status, or sexual orientation; and are an equal opportunity employer.
This publication will be made available in alternative format upon
request to people with disabilities (701) 231-7881.
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