On 25/9/06 1:58 PM, "John Evans" <johne@heritageseeds.com.au> wrote:
Vaughan Jones replies -
There are lots of toxic plants in pastures.
Toxic Plants
Sudden deaths can be caused by consuming poisonous weeds such as Ragwort
(sheep are immune provided quantities are not excessive for prolonged
periods), Foxglove, Rhododendron, Azalea, Delphinium, Yew, Oleander (takes
only 50 grams or one mouthful to kill a cow), Arum lilies, wilted or
stressed cherry leaves (high nitrates), many bulb plants and some mushrooms.
Some of the above are grown in gardens and animals can be killed when
unsuspecting homeowners trim them and throw the clippings over the fence
with the thought that the animals will appreciate them. If your garden or
any neighbours have any of these plants it would pay to warn them.
Plants such as buttercup (ranunculus) in large quantities can also cause
problems, some cultivars more than others. Horse tail, a type of fern, and
bracken ferns can be toxic. Avoid too much of these getting into hay or
silage.
There are also trees which cause abortions such as cypress and pine trees
(Cupressus macrocarpa, Pinus radiata and others). They vary in their
toxicity depending on how much is eaten, amount of stress, stage of
pregnancy and time of year, but it is best to treat them all as toxic,
especially their dead leaves and seed pods, both of which can blow some
distance into pasture and then be eaten by grazing stock. After storms check
for trees and branches blown into areas accessible by stock. Sources include
logging and discarded Christmas trees.
Abortions may begin within two days or not occur for two weeks after eating
needles. Very few needles can cause an abortion. Incidence can vary from
only a few abortions to all. There are no toxicity signs. A live calf can be
born if near calving.
Many parts of oak trees, including acorns, are toxic to cattle, especially
young stock. Avoid animal access, especially if hungry or on lush pasture so
craving roughage.
Pigs have a much more powerful digestive system and eat acorns apparently
without troubles, however, anything toxic can cause problems if consumed in
large enough quantities.
Some toxins can cause eczema - skin peeling off bare parts such as face and
udder.
Children are inclined to put things in their mouths so care should be
exercised by not having poisonous plants within their reach and by educating
them about poisons.
Other Causes of Poisons or Toxicities
Algae in water troughs or stagnant pools frequently kills animals in
Australia during the late summer heat. In New Zealand Iıve seen it make
calves scour like coffee. Clean all water troughs at least every three
months, especially in summer and before calves enter a paddock.
Blue lupins, fathen, sorrel, pigweed, bracken fern, Ragwort, some buttercups
(Ranunculus), Amaranthus (Redroot), Olieanda, St Johnıs wart, buckwheat,
radishes, Johnson grass (Sorghum halepense), musky storksbill, Panicums,
ngaio, lantana, wild cucumber. Then there are straight out poisons such as
lead and the swallowing of nails and wire.
Some plants become toxic when wilted, so beware of prunings and hedge
cuttings thrown over a fence by a well intending neighbour feeding your
animals.
High manganese (Mn) levels in pastures and water is not a toxin, but can
stress animals as can any excesses. Check your Mn levels in pasture and
water. Adequate draining and liming reduce Mn levels in pasture, aerating
and filtering reduces it in water.
Fruit orchards which have had sprays for many years can be a problem,
however soils and leaves from grasses can be measured. Copper could have
been used extensively, so sheep can be adversely affected because they
suffer if Cu levels are too high. Grazing them on other pastures inbetween
grazing the orchards can reduce this problem. Lead and arsenic can also be
present at high levels.
Symptoms
These are many and varied, so if health problems occur check what is being
eaten. Quite often just one or two animals will be affected, possibly
because they have over-eaten on the plant concerned or are more allergic
than others.
Causes
These vary depending on the plant, but usually prolonged feeding is
necessary.
Prevention
Never graze, feed cut or harvest and feed toxic weeds or plants.
Livestock grazing on plants or fed mouldy cereal grains during drought
conditions could run the risk of being poisoned, causing illness and even
death.
During dry conditions and feed shortages, livestock are more likely to
consume toxic plants.
Ragwort, some buttercups, holly, ivy, rhubarb, convolvulus and brackenfern
are toxic plants.
Treatment
Remove the source and fully feed on safe feed and phone the vet.
Liver Damage
Toxins and poisons can damage livers. Outward signs include the animals skin
being slightly jaundiced (light yellow brown) and/or the skin on the brisket
and under the front leg becoming a yellow/brown colour. The stronger the
colour and the larger the area, the worse the liver damage. In severe liver
damage cases the skin on bare areas (around face, udder etc.) can peel.
Avoid buying animals with any of these symptoms. Those you own should be
well fed with a variety of feeds rather than say all brassicas, all annual
ryegrass, etc., and cared for with zinc, energy and mineral supplements.
Some fish and seaweed based animal tonics are reported by many farmers to
help affected animals recover.
Moulds (also see Silage > Moulds)
Aflatoxins produced by Aspergillus flavus affect organs such as the liver,
kidney, heart and adrenal glands and can cause cancers. Symptoms include
feed refusal, reduced growth rate, decreased feed efficiency, and decreased
milk production. In addition, listlessness, weight loss, rough hair coat,
mild diarrhoea, anaemia with bruises and subcutaneous haemorrhage, impaired
immune system response, increased susceptibility to disease, and rectal
prolapse may be observed. The disease may also impair reproductive
efficiency, including abnormal oestrous cycles (too long or too short) and
abortions.
The severity of aflatoxicosis varies with the animal species, level of
aflatoxin in the diet, and the duration of exposure to aflatoxin. The
diagnosis of aflatoxin poisoning is difficult because of the variations seen
between animals and farms, but liver damage is a common observation.
Aflatoxins cause the liver to become pale tan, yellow or orange. The
prognosis of aflatoxicosis depends on the severity of liver damage.
While the recommended feeding level of aflatoxins are 0 parts per billion
(ppb), the level of toxins an animal will tolerate will depend on the breed,
age, sex and health status of the animal, and management level of the farm,
for example how well fed.
Mould can grow on grain, silage, hay, or in the base of pasture after rain
when the brown material rots and goes mouldy. Maize silage, without a mould
inhibitor, or any silage if left uncovered at the feeding face, can grow
mould and cause foetus losses. The pH of maize silage should be 4 or lower
to reduce mould growth. Mouldy parts should be fed to empty animals, or
better still, discarded.
Where topping is necessary it is best done before grazing because it is
cleaner, doesnıt spread dung all over the pasture and increases dry matter
intake of the cows because some of the moisture is eliminated when wilted.
Moulds, fungi, algae and some insects can cause toxins in grain, dead damp
pastures, hay and/or silage and in drinking water growing algae. Enlarged
mammary glands producing milk can occur in pregnant heifers after eating
mouldy maize.
It takes moisture, warmth and air to grow mould. Dry hay will not have
mould, damp will, sealed vacuum silage will be free of mould while loosely
packed and uncovered silage will.
Some species of earthworms reduce dead material by consuming it as is, and
some by taking it into their burrows. However, pasture with optimum numbers
of earthworms can still have infectious amounts of mould unless it is short
(less than about 200 mm (8²)) fresh, green and growing and is not grazed
into the mould zone. To clarify this, even 50 mm (2²) pasture can have
mould, in fact can be half mould, if it was left behind from longer pasture
or was dry from drought before growing after rain. Even longer than 200 mm
fresh green growing pasture may not have ingested mould if animals are not
made to eat the base. As pasture lengths before grazing gets longer so does
the mouldy base. Making milking cows, growing stock or fattening animals
³clean up² paddocks and eat long pasture down to a low residual, causes them
to produce less.
Animals in nature would not eat old mouldy pasture, but graziers with both
controlled grazing and uncontrolled grazing can make them do so. You could
question how uncontrolled grazing could force them to eat old mouldy
pasture. I've seen animals in many countries set stocked in paddocks for
much too long, so they were grazing long pasture down to the yellow or dead
mouldy material near the base.
Ergot alkaloids in some seed heads reduce feed intake and adversely affect
body temperature regulation. Ryegrass and Paspalum (Dallis grass) seeds in
hot humid conditions can develop a fungal toxin which causes severe hind
limb lameness. Infected seeds double in size and sometimes become mouldy and
dark in colour. The toxicity can progress to gangrene with sloughing of the
skin, ears, tail switch and tissues around the hoof. In severe cases animals
have to be euthanized. Ergot is caused by a fungus known as Claviceps
purpura or Claviceps paspalum. The severe form is so rare that most
veterinarians have only seen it in textbooks. Quantities of the infected
seeds when grazed or fed in conserved feed can be dangerous. Brahman type
cattle have less trouble with this than English and Continental breeds.
Toxins can add to the ill effects of facial eczema and endophyte toxicity.
Solutions
Avoid the above. If pasture is long and has mould at its base, graze it down
in stages (nipping the top off at weekly intervals) to allow sunshine, the
best exterminator of mould, to get to the lower levels before the next
grazing. If it is in just one large paddock, use an electric fence to
achieve the same. If in an area with little sun as in parts of the UK this
wonıt work.
Applying lime on a regular basis encourages earthworms which reduce dead
pasture material.
Measuring Moulds
Check with your vet then collect pasture as you would for facial eczema,
i.e., many samples across a paddock ready to be grazed, cutting the grass
right down to the lowest grazing height, especially under the long patches.
Avoid collecting any soil.
Samples can be delivered or sent to AgResearch, East St, PB 3123, Hamilton.
Charges are $75 minimum and $100 to identify fungi, but they donıt tell you
how to avoid the toxin.
Measuring toxins does help tell you where the problem are.
Ruakura discovered that a fungal toxin called Fusarium lowers ewe conception
rates. They are now working on the possibility that cows may be also
affected, although they know that cows are not as sensitive to the toxin as
are ewes. The fungus grows on dead pasture which goes mouldy after rains,
especially in humid autumns.
More coming.
Best wishes,
Vaughan Jones
Hamilton
Waikato
New Zealand
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