Vaughan Jones replies to John re toxic pastures.
Prussic Acid (PA)
Sorghums, Johnson grass, Sudan grass contain cyanide which causes prussic
acid poisoning, so can be unsafe to graze, except after plants reach
maturity and no rapid growth is occurring. Frost and drought stress increase
it.
Silage from high cyanide plants can have high levels of cyanide which can
gas off when fed out, so with all cyanide containing plants and their
silages, measure the levels.
Sorghums come under many commercial brand names so know what you are
growing, or better still grow safe crops, not dangerous ones. Some sorghums
are safer than others.
I have never grown sorghums and have not recommended dangerous ones because
there are enough problems in farming without buying them. At night, or if
you are off the farm, and animals break into a dangerous crop many can die
within a few hours.
Grazing crops such as Johnson grass, which incidentally is a noxious weed in
New Zealand, can be catastrophic with whole herds dying in short time on
light soils, while in other areas with heavy clay soils and more even
rainfall the problem hardly occurs, but one should never take chances - grow
safe crops and measure levels of dangerous ones. Prussic acid-free crops can
kill animals with nitrate poisoning. See Nitrates.
Causes
Cattle consuming cyanide toxic species are susceptible to prussic acid
poisoning because the plants produce cyanide while growing, and more so
after:
€ Anything damages plants or changes their growth pattern from slow to fast
or fast to slow.
€ Trampling before grazing.
€ Frost.
€ Heat.
€ Drought
€ Sudden rain after even a mild dry spell. On sandy soils the ³after
drought² effects are worse than on clay soils.
€ Any growth pattern change or lack of nutrients.
PA congregates in the young leaf tips that animals like and eat first. Once
mature, the levels are lower, but measuring is still recommended.
Pigs and horses can detoxify the cyanide, but with cattle it takes longer.
Symptoms
Affected animals have:
€ Increased rate of respiration.
€ Increased pulse rate.
€ Gasping.
€ Spasms and/or convulsions.
€ Trembling and muscular twitching or nervousness.
€ Foaming at the mouth.
€ Blue coloration of the lining of the mouth.
€ Bright red blood.
Severe nitrate toxicity causes are similar as are the animal symptoms, but
with it the blood is brown.
Clinical signs are seldom seen because animals die within 15 to 20 minutes
from respiratory paralysis.
Zero to 25 mg per 100 grams of plant dry matter are considered safe for
grazing, 50 to 75 is risky, and over 100 highly dangerous, but check with
neighbours, your vet and with the supplier of the test kit.
Prevention
Grow safe crops, but if you have dangerous ones don¹t graze them until
mature and remember that this applies to the regrowth and that PA can kill
animals faster than you can do anything to prevent them dying.
PA levels decrease after cutting so it is no good posting samples to
laboratories. You should have your own testing kit and know the toxic
levels. Also measure for nitrates.
Keep sodium, sulphur and molybdenum levels at optimums in pastures by
fertilising correctly feed sodium sulphate if more than 30% of the diet is
from toxic plants.
If you have PA plants ready to graze, but high in PA you can mow them and
leave them lying for a few days and PA will decrease. Don¹t rely on this
phenonemum - measure the level. Making toxic crops into silage or hay
reduces the cyanide, but testing is still advisable. Nitrate test strips
turn different colours depending on the nitrate levels which should be below
1,000, but sunless weather can make this difficult.
Ensure that the animals do not enter the paddock hungry.
Legume Toxins
Cattle can suffer bloat and sheep can suffer ³Clover disease² from excess
oestrogen in some clovers, mostly reds and subterranean clovers. High levels
of oestrogen can adversely affect fertility, mostly in sheep in autumn.
While cattle will usually (but not always) eat clover first, sheep will
sometimes leave it if it is long, possibly to avoid estrogen.
Scientists are endeavouring to breed condensed tannins into white clovers to
counter their bloat effects and some are trying to reduce oestrogen levels.
Lucerne can cause severe bloat and copper toxicity in sheep and if insect
damaged can develop oestrogen.
Potassium
Potassium levels in the food should really not be much above 1%, however
fast growing pasture needs about 2.8%. Once pasture levels exceed 3.6% K
(many exceed 4%), pasture becomes unpalatable to livestock and even slightly
toxic, and the pasture clover percentage starts decreasing, which then
lowers the percentage calcium and magnesium in the pasture.
Milk Urea Nitrogen (MUN)
High N intake relative to carbohydrate and sugars (energy) intake cause
cattle to use some of the N to digest the surplus and excrete the surplus in
the form of ammonia in the urine. Urea levels in blood and milk also rise
and lower the conception rate. Grazing short lush pastures, especially if
artificial N is applied, is when problems can occur. Symptoms are burn
patches of dead pasture where the cattle passed concentrated urine. These
pasture burn patches are worse in heat when cattle perspire more and when
potassium levels are high in pasture because excess K is also excreted in
the urine.
Milk urea nitrogen (MUN) analyses can help you determine if there¹s a
problem. If there is, allowing pasture to grow longer before grazing can
help. MUN levels above 18mg/dl can decrease conception rates, and indicate
that protein should be lowered and/or carbohydrates increased. See
GrazingInfo > Elements > Nitrogen.
Water
Water is best when it has no nitrate N, especially when for children, but 10
ppm is the World Health Organisation safety limit for adults, although some
adults are not affected by 20 ppm.
To get nitrates measured in water take 50 ml from as near the source as
possible to a laboratory. There are also paper strips available.
Clean all water troughs thoroughly at least twice a year to stop algae
growth increasing the water's nitrate content. Preferably there should be no
nitrates in animals¹ drinking water, but it should certainly not exceed 10
ppm. 50 ppm nitrates in water can be toxic to stock.
Ensure that water is free of it, and that phosphorus, molybdenum, sulphur
and boron levels are adequate in soils by analysing pasture before sowing
crops and by fertilising as required. If N and K are high and phosphorus,
molybdenum, sulphur and boron are low, NT can be worse.
End
You can email me some photos of tails, cows, high producers and low
producers and I can comment on them.
Excerpts from book -
Footrot. Infection can enter a damaged part of the hoof and a foul smelling
discharge can occur. In correctly fed grazing animals this is rare unless
lanes and concrete are rough with stones or are too cambered which twists
and opens the hoof, or daily walking distances exceed two miles (3 km) a day
and if the herd has an excess of genetics with weak hooves. Agricultural
lime or lime chips on lanes reduce it. It is more common in animals standing
on concrete for long periods and grazing pasture in muddy soils, with soft
hooves and low in zinc. Hoofmats containing copper sulfate reduces
infections and with zinc sulfate and hardens hooves. See www.sweetmans.co.nz
and www.shoof.co.nz for international distributors. Early treatment is
important. If not treated, the infection can go deeper and into a joint
Hooves sore. Toxicity from endophyte fescue which causes swelling between
the dew claws and hooves which eventually slough off. See Footrot, Laminitis
and Walking.
Hooves cracked. Low zinc, old age. See Footrot, Laminitis, Hooves sore and
Walking.
Hooves soft. Low zinc. See Footrot, Laminitis, Hooves soft and Walking.
Lameness. Causes include low zinc, stone, twig or wire in hoof, standing on
hard surface for too long, acidosis (usually in spring), rumen pH drop, low
or high selenium levels, or low boron causing a stiff gait, endophyte
toxicity from, Perennial Ryegrass or Fescue Staggers (usually in summer).
Hypomagnesemia (Grass Tetany) sometimes called Grass Staggers can look like
just lameness.
Lameness Laminitis Footrot
Control
Feed concentrates (GF) after grazing and at least twice a day, rather than
in one feed on an empty rumen. If it has to be fed during milking then give
the cows pasture, lacerated or long-cut silage, or hay before milking.
Treatment
Most of this section is on prevention because infection and treatment are
expensive, so eliminate the causes. Unless experienced, a vet should be
called.
In all lameness, the sooner treatment is effected the less the problem will
be and the sooner it will mend. Lame cows which are grazing can lose
condition rapidly. Keep them in a close paddock with lots of mature pasture,
hay and silage. A Shoof (shoe for a hoof) may have to be used to spread the
weight and reduce pain (see www.shoof.co.nz).
Check for stones, nails, wire or thorns causing the hoof damage.
If the lane is causing lameness, calculate the total cost of time, vet
bills, lowered milk production at the time and subsequently, medicines and
the likelihood of missing a mating and possibly being culled. They could
total $300/cow which may make you will feel better about spending money on
fixing the lane.
Old cows and those prone to lameness may need to be always grazed in close
paddocks. Walking long distances on a stony, rough, muddy or in a bunched up
mob where they can¹t see where they are putting their hooves will increase
lameness.
Laminitis
This is swelling of the sensitive part of the hoof, cutting off blood flow
to the bone part of the hoof which then becomes soft and weak and easily
bruised or damaged by small and large stones and by twisting as on rough
uneven stony lanes and ones with too much camber (slope down from centre).
Laminitis occurs mostly in cows in confinement and/or fed excess GBF
(especially if at one feed a day on an empty rumen), or silage and hay which
has been chopped too short and/or total mixed ration (TMR) wagons which are
allowed to mix and chop silage and/or hay for too long a period so it
becomes too short. This short feed is swallowed quickly with little chewing
and not regurgitated as much as it should be, so little saliva is made and
consumed. Causes also include anything else which causes poor digestion and
acid rumens and insufficient long material and cud chewing. High-nitrate
pastures and acidosis can bring on laminitis.
The problem is worse if problem feeds are fed to hungry animals.
The first sign is lameness which can vary from scarcely noticeable to severe
in one or more hooves. The cow could also appear off colour, nervous and/or
shaky.
Saliva is the first digestive juice and contains sodium. Adequate sodium in
the ration or if fed as a supplement with minerals through the drinking
water increases saliva manufacture by ruminants and gives a healthier rumen
and up to 12.5% more milk in sodium deficient areas. Dairy farmers who start
feeding Solminix as a drench or better still dispensed in to the drinking
water, notice a substantial increase in saliva dropped where the cows stand
in the milking parlor and chew their cud.
Adequate mature pasture or forage crops fed with the GF and lacerated silage
which is long-cut and bruised help reduce the problem.
If GF is fed and the silage is fed separately from the GF and is finely cut
(under 5 cm - 2 inches), there can still be problems. It is best to feed
forage before feeding GF at milking and to feed finely cut silage after
grazing pasture. Long-cut silage (8 cm and over) is usually OK and much
better for animals in many respects because they don¹t guzzle it and can
regurgitate it. Feeding a couple of kg (5 lb) of good normal length hay
spread over 24 hours can reduce the problem, but it is better to remove the
cause and feed mature pasture and lacerated or long-cut silage. Remember
that ruminants were made to eat reasonably quickly and then chew it
(regurgitate).
Laminitis and acidosis can occur when grazing pasture or eating silage which
is too short because it is swallowed without much chewing and may not be
regurgitated much. This can occur in sappy first-grazing spring pasture in
snow-covered areas, and in milder climates when the second grazing round
starts, after the longer winter saved pasture has all been grazed,
especially if sunshine is lacking and too much nitrogen has been used. It
can also occur following dry summer periods on short lush pasture grown
rapidly after autumn rains.
Digestive disturbances, and so laminitis and/or acidosis, can be aggravated
by any sudden change of feed instead of being done over about ten days.
Laminitis can also be a secondary problem of ill animals sick from any cause
including stress - from hunger (long periods without feed caused by being
hungry before milking and then off pasture for hours while being milked),
mineral deficiency, cold (not eating during cold winds causing animals to
stand tail to wind and not eat for hours), heat (not eating, having to walk
long distances in heat), being in season (on heat, cycling), etc. A lack of
sodium adversely affects animals¹ ability to control body temperature, so
they then suffer more in cold and heat.
Best wishes,
Vaughan Jones
Hamilton
Waikato
New Zealand
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