Effects of Mycotoxins on the Health
and
Productivity of Beef Cattle
Aflatoxin and other mycotoxins can have considerable effects on
beef
cattle although the
problems
are usually less critical than for swine and poultry. Consumption
of
feeds highly contaminated
with aflatoxin may reduce growth rate and increase the amount of
feed
required per pound of
gain.
Calves are generally more sensitive to feed contamination than
adult
cattle. In affected calves,
some cases have revealed severe rectal straining and a prolapsed
rectum. Lactating cows show a
significant reduction in milk yield. Research has shown that high
levels of aflatoxin can also cause
liver damage in adult cattle. Feeding a high level of aflatoxin
may
also depress immune function,
resulting in disease outbreaks.
Based on the feeds available, those contaminated with aflatoxin
should
be fed at the lowest level
possible and for the shortest period of time practical. The
effects of
aflatoxin fed to cattle depend
on the level of aflatoxin in the ration, the length of the
feeding
period, and the age of the animal. If
aflatoxin-contaminated feeds must be fed to beef cattle, follow
these
guidelines (on a dry matter
basis):
- Creep feeds and diets for gestating and lactating beef cows
should
contain less than 20 ppb of
aflatoxin.
- Unstressed, growing-finishing cattle in excess of 400 pounds
may
be fed diets containing up
to 100 ppb of aflatoxin.
- Diets for stressed feeder cattle should contain no more than
20
ppb of aflatoxin. Stressful
conditions include weaning, shipping, extreme heat or cold,
diseases,
and parasites.
- Animals destined for slaughter should receive aflatoxin-free
diets
for at least 3 weeks before
slaughter.
Since cattle in the southeast are typically fed high forage
diets,
they are usually fed grain only as a
supplement. Thus a relatively high level of aflatoxin can occur
in the
grain before it exceeds the
tolerable dietary level. In general, cattle will eat about 2.5
percent
of their body weight as dry
matter. This can be used to calculate the contribution of grain
to
their total ration, and the
tolerable
level of aflatoxin in the grain. For example, growing calves
weighing
600 pounds will consume
about 15 pounds of total feed (600 lb multiplied by 2.5% equals
15 lb). If they are fed
3 pounds of grain plus
forage-to-appetite, the grain will make up about 20 percent of
their
total diet (3 lb divided by 15 lb equals
20%).
In this case the grain may contain up to 500 ppb of aflatoxin
(100 ppb
divided by 20% equals 500 ppb).
Aflatoxin levels allowable in the grain, given different rates of
inclusion in the beef ration, are
illustrated (Table 5).
Table 5. Allowable Aflatoxin in Grain for Beef Cattle
Percentage of Grain Aflatoxin Level in Total Diet
in Diet 20 ppb 50 ppb 100 ppb
20% 100 ppb 250 ppb 500 ppb
40% 50 ppb 125 ppb 250 ppb
60% 33 ppb 83 ppb 167 ppb
80% 25 ppb 63 ppb 125 ppb
This table assumes that aflatoxin is contained only in grains.
This assumption is not always correct. Each dietary component
should be tested for aflatoxin prior to use of any contaminated
grains.
Heat stress, marginal nutrient plane, crowding, disease exposure,
the presence of more than one mycotoxin, and drug interactions,
as well other factors, increase animals' susceptibility to
mycotoxins.
Thus these recommendations must be tempered with knowledge of the
animals involved.
Other mycotoxins (DON, T-2, and zearalenone) present in grains,
silages, and hays may cause
problems with performance and immune status of beef cattle.
However,
little research is available
on the levels of the individual toxins that may be tolerated by
animals. In cases of disease
outbreaks and reproductive problems, the feed should be tested
for a
full range of mycotoxins.
Large producers should consider routinely screening feeds for
mycotoxins.
Until further information is available, the producer should limit
dietary mycotoxins to the levels
listed (Table 6).
Table 6. Maximum Mycotoxin Levels for Beef Cattle
MYCOTOXIN LEVEL
DON 500 ppb
T-2 100 ppb
Zearalenone 250 ppb
Fumonisin 50,000 ppb
Heat stress, marginal nutrient plane, crowding, disease exposure,
the presence of more than one mycotoxin, and drug interactions,
as well other factors, increase animals' susceptibility to
mycotoxins.
Thus these recommendations must be tempered with knowledge of the
animals involved.
Prepared by
Mary Beth Genter, Extension Toxicology Specialist
Winston M. Hagler, Director of NCSU Mycotoxin Laboratory
Jeff A. Hansen, Extension Animal Science Specialist
Bob A. Mowrey, Extension Animal Science Specialist
Frank T. Jones, Editor, Extension Poultry Science
Specialist
Matt H. Poore, Extension Animal Science Specialist
Lon W. Whitlow, Extension Animal Science Specialist
http://www.ces.ncsu.edu/gaston/
