C64ancastar Farming, Saturday, July 19,1986
Prussic Acid, Nitrate Can Be Toxic In Drought-Stricken Forages
COLLEGE PARK, Md. - A
drought year like 1986 can turn
certain forages into poisonous feed
for livestock. Some thoughts on
how livestock and dairy fanners
can cope with this phenomenon
have been assembled by Lester R.
Vough and E. Kim Cassel, Ex
tension professionals at the
University of Maryland in College
Park
Severe drought occurring
throughout much of Maryland and
southeastern Pennsylvania this
year is cause for concern by
livestock producers-not only
because of reduced feed supplies
but also because of the potential
for livestock poisoning. Drought
stress increases the risks of
prussic acid poisoning in
sudangrass, sorghum, and
sorghum-sudangrass hybrids.
Severe drought conditions also can
result in nitrates accumulating in
these plants as well as in com.
Prussic Acid
Sudangrass and sorghum
produce cyanogenetic glucosides
during their growing stage. Plants
producing cyanogenetic glucosides
are sometimes referred to as
cyanogenetic plants. Glucosides
are compounds that break down or
decompose into glucose sugars by
hydrolysis (addition of water). In
cyanogenetic plants this decom
position process releases cyanide
and it becomes toxic hydrocyanic
acid-frequently called prussic
acid-abbreviated HCN.
Under normal growing con
ditions, the intact glucoside occurs
in the plant. When plants con
taining such glucosides are eaten
by animals, they are readily
eliminated before enough con
centration occurs to be harmful.
However, certain conditions in
volving climate, fertility, stage of
growth, and anything that retards
plant growth and development
may increase cyanogenetic
glucosides in the plants.
A rapid regrowth following
retardation favors the increase of
II J —=
30 YEARS AGO
-According to the Department of
Agriculture, all Pennsylvania
farm field crops except oats have
recovered from adverse spring
weather. The total yields at har
vest are now expected to be
greater than last year.
- What is perhaps one of the oldest
farm organizations in the nation,
the Octarara Farmers Club will
celebrate its hundreth anniversary
in August at the middle Octarara
Presbyterian Church. The farm
organization was founded by 11
farmers with mutual agricultural
interest. Howard Walton has
family members who were
associated with the farmers club
for more than 50 consecutive
years.
-Eight hundred and three new
members have been admitted to
the Holstein Freisian Association
of American. This brings total
membership in the association to
an all time-high of 46,713.
-Members of the Bareville
Church of the Brethren have
contributed three bred dairy
heifers that joined a shipment of 23
sent to needy families in West
Germany by the Heifer Project,
Incorported.
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glucosides. Wilting and frost injury
may cause a rapid increase of
hydrocyanic acid (prussic acid) in
a plant that would otherwise have
been nontoxic.
Sorghum is much higher than
sudangrass in prussic acid; and, in
general, it is unsafe for pasturing
except after plants reach maturity
and no new growth is present. As a
group, sorghum-sundangrass
hybrids also contain more prussic
acid than sudangrasses.
Sorghum silage may contain
toxic quantities of prussic acid, but
ithe acid escapes in a gaseous form
when the silage is moved and fed.
Under most circumstances, silage
and well-cured stalk residue can be
fed with safety. Prussic acid is
released very quickly from the
glucoside form in frozen leaves.
Thus frosted sorghum is very
dangerous until it begins to dry
out.
Usually there is little danger of
prussic acid poisoning in grazing
most varieties of sudangrass.
However, the young growth that
follows clipping, drought, frost, or
grazing may contain appreciable
quantities of prussic acid.'
Stage of growth. Leaf blades
normally contain higher levels of
prussic acid than leaf sheaths or
stems. Tillers and branches have
higher levels than older plants
because they are mostly leaves
with little stalk material present.
Upper leaves contain more prussic
acid than older leaves. The prussic
acid content of sudangrass and
sorghum is highest in the earlier
stages of growth.
As plants mature, the stalk
content increases, causing the
prussic acid content in the total
forage to decrease. However, the
hazards associated with poisoning
decrease only slightly with age if
animals selectively graze the more
tender new growth-those plant
parts high in prussic acid.
When, due to drought, water is
withheld from sudangrass which is
less than 18 inches in height, a high
THIS WEEK
-John W. Eshelman and Sons,
North Queen Street, Lancaster,
have announced plans to construct
a feed mill in Chamblee, Georgia,
with completion expected early
next year. Most of the raw
materials to be used in the
manufacturer of feeds, about 350
tons daily, will come from Lan
caster county. Other Eshelman
plants are in Pennsylvania, Ohio,
North Carolina and Florida.
-Increased farm milk prices for
the last six months of the year are
forecast by Dr. C. J. Blanford,
marketing administrator of the
New York Metropolitan Milk
Marketing area. Milk production is
expected to be slightly under that
for last year. “Uniform prices to
farmers should average 19 cents
per hundredweight, above those
for the last half of 1955,” the ad
ministrator said. Prices paid by
handlers for fluid Class 1A are
forecast at 16 cents per hun
dredweight over those of a year
ago. The average uniform price for
the last six months is estimated at
$4.36 per hundredweight. For Class
1A prices the average is predicted
to $5.52 per hundredweight.
prussic acid content may persist
because the grass is unable to grow
out of the high prussic acid stage.
Thus, drought probably operates
as a factor-largely by keeping the
plants small, in which stage they
are generally higher in prussic
acid content than when larger.
Utilizing Potentially
Hazardous Forages
Pasture. Deaths on pasture are
partially caused by animals
preferring to graze leaves and
young shoots. These plant parts
may contain two to 25 times more
prussic acid than stems.
Sudangrass should not be grazed
until it has reached a height of at
least 18 inches.
Green chop. Green chop forage
is usually safer than the same
material used for pasture because
it is not selectively grazed. In the
case of pasture, only the leaves
may be eaten; with green chop
material, the total plant is con
sumed. Stems may be regarded as
safety devices, since they dilute
the high prussic acid content of the
leaves.
Wilted silage. Silage is generally
safe for feeding. It may contain
toxic levels of prussic acid while in
storage, but much of the poison
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escapes as a gas when the silage is
moved for feeding. Do not feed new
silage for at least three weeks after
ensiling.
Hay. The prussic acid content of
sudangrass hay decreases by as
much as 75 percent while curing
and is rarely hazardous when fed
to livestock.
Environmental factors con
trolling nitrate accumulation in
plants are fertilization, light in
tensity and drought. Generally
there is a direct response in plant
nitrate concentration to Lscreasing
fertilizer N, and nitrate ac
cumulation is greater from am
monium sulfate or urea. Nitrate
accumulation also is greater with
delayed applications of fertilizer.
Both low light intensity and
drought conditions increase the
concentration of plant nitrate.
In a Missouri study, sudangrass,
orchardgrass, and tall fescue
accumulated nitrate at high
levels; smooth bromegrass,
timothy and ladino clover were
intermediate; and alfalfa, Ken
tucky bluegrass and wheat had
only low nitrate levels. Pearl
millet builds up higher con
centrations of nitrate than does
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sudangrass. Most plant in
vestigations show that nitrate
concentrations reach their
maximum value at the pre-bloom
stage and then gradually decline
with age.
We have had questions con
cerning harvesting com that is two
to three feet tall- in some cases in
tassel-com that is considered to be
a crop failure at this point. The
growers are considering planting
another crop such as sudangrass
or sorghum. Since nitrate con
centrations reach their maximum
level at the pre-bloom stage,
nitrate levels in this com could be
potentially high enough to be toxic.
Drought conditions are different
this year than in 1983. Very few of
the feed samples analyzed for
nitrates in 1983 were high m
nitrate. But the drought conditions
occurred later in the season m
1983, and com generally had more
growth.
It is recommended that drought
stressed sorghum-sudangrass or
com harvested for hay or silage be
analyzed for nitrate. While har
vesting as hay or silage generally
will alleviate prussic acid
problems, it may have little, if any,
effect on nitrate levels
rwmnm
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