On 25/9/06 1:58 PM, "John Evans" <johne@heritageseeds.com.au> wrote:
Vaughan answers -
Fescues and toxins
Cattle donıt like any fescue once it gets longer than 20 cm, but of course
theyıll eat it if made to.
The best modern safe-endophyte fescues should still be grazed when no longer
than 15 cm high when if with clover cattle will eat it almost as willingly
as they do perennial ryegrass.
There are lots of other toxins in pastures.
Toxins
All feeds, including pastures, have the potential to produce toxins which
affect animals adversely. Some plants are OK when green and growing, but can
become lethal when growing very fast (high nitrate plants such as annual
ryegrasses, sorghums, Nutrifeed, maize, etc.), stressed through wilting
(cherry tree leaves), flower (some brassicas), seed (high endophyte
ryegrasses), die in moist warn conditions (grow facial eczema spores) and
others. Some are local problems, so learn from neighbours and local vets
about problems in you area.
Toxins in mould of wet old grass, mouldy hay or silage can cause severe
problems in the rumen and can increase somatic cell counts in milk.
Grains and grain byproducts are the most common sources of toxins. They
should be stored with less than 14% moisture and not crushed, kibbled or
rolled until ready to feed, and always be fed within a week of processing.
Maize silage may also be a source because the ensiling process does not
destroy the toxins already in cobs. Any silage which has mould or near to
mould can be toxic.
The fungal toxin called Fusarium in pasture lowers ewe conception rates.
Cows may be also affected, although cows are not as sensitive to the toxin
as are ewes. The fungus grows on dead pasture at the base of a mouldy sward,
especially in humid autumns.
Moist humid weather encourages moulds, some of which are harmless to
animals, but can affect feed value and palatability. Some affect animal
health and production and can cause liver damage which can slow growth,
decrease production and cause slips or abortions.
Conditions which cause the infertility also cause facial eczema so there are
two good reasons for farming to prevent them. All moulds and fungi affect
animals adversely so should be avoided, including old toppings (clippings)
and mouldy hay or silage
Sometimes what is thought to be a toxin can be something else. An example is
after Army caterpillars eat pastures, grazing animals can die. Kikuyu can
become unpalatable and even toxic after damage from insects such as army
caterpillar. What happens is that army caterpillar chews it down to the
ground and leaves a lot of manure behind. The Kikuyu then grows vigorously
and has incredibly low magnesium levels, so low that animals not fed other
high Mg diets with the Kikuyu can die.
It takes moisture 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 will.
Females can lose their foetus and all can suffer liver damage from moulds on
grasses, even without toxic endophyte - some endophytes are more toxic than
others.
Sweet clover (Melilotis albus and M. officinalis) can be an excellent
grazing legume, but a problem can occur if sweet clover hay is mouldy. When
livestock consume too much mould in Sweet clover hay it prevents blood
clotting.
All moulds should be avoided in hay, silage and pasture.
Many of the above problems are not as severe in the cooler areas where they
donıt need high endophyte grasses and there is less heat and humidity.
The ³Simply not feeding enough³ is common. Over the years I have been phoned
by many farmers because their cows were not producing well enough. On
visiting them I would find that they were feeding their Jerseys only about
12 kg dry matter instead of 17.
Toxic weeds such as some buttercups, ragwort, Amaranthus, in pastures can be
a problem especially if harvested in silage and sometimes in hay.
Fusarium
Fusarium head blight is a fungal disease that can infect a number of crops
including grain crops (wheat, barley, oats, rye, corn, canary seed) and
seeding forage grasses. In dry summers less develops than in moist humid
ones.
Toppings (clippings) and dead grass at the base are a source of nutrients
for Fusarium and other fungi. Fusarium are free living and produce
zearalenone which is a phyto-oestrogen ergovaline which adversely affects
animal fertility.
In summer and autumn under warm dry conditions or after autumn rains,
fusarium produces Zearalenone on decaying grass. It is a fungal toxin which
is oestrogenic and causes a reduction in ovulation and fertilisation rates
in ewes resulting in fewer twins and more empties. It's a major problem for
sheep farmers as it reaches it's peak when the rams go to the ewes. It
occurs when days are warm and nights are cool, but below about 6 degrees C
at night reduces it.
Topping or mowing part of the paddock ahead of the cows can cause a problem
if all is not eaten and it is then consumed at the next grazing.
One can smell mould by breaking long grass off at ground level and smelling
the 7 cm yellow base of the plant. Cows normally donıt graze this unless the
40% grazing rule is broken, but when mown before grazing they do eat it. The
mouldy smelling base of pasture is not not always fusarium infected. Blood
and pasture can be tested for this by doing about six assays. Consult your
vet.
Testing for the toxins isnıt easy or guaranteed to give accuracy of the
on-farm problem, partly because toxins can occur in pockets over a pasture,
so collecting samples can miss them. Sun facing slopes can have more than
shady ones.
Prevention
To prevent fusarium adversely affecting ewe fertility flush them on 70 to
100 mm (3² to 4²) pasture that is "green to ground". Avoid too much clover,
especially red, both of which can have the same effect on conception rates,
especially with sheep. ³Clean² oestrogen-free clovers are being developed.
Mycotoxins (fungus poisons) are neither infectious nor contagious between
animals, but can occur herd-wide from what is eaten.
Controlled grazing should include avoiding hard grazing of toxic material by
in-calf cows and heifers because the highest levels of the Zearalenone which
is the oestrogenic mycotoxin produced by the Fusarium fungi, are at the base
of the pasture. If mowing a portion of the paddock the day before grazing,
ensure that all the cut grass is eaten, because that left until the next
grazing a week or two later could become mouldy - and provide a facial
eczema spore haven. Try and avoid topping after grazing because fusarium
could grow on toppings. Donıt allow in calf cows or heifers into paddocks
immediately after cutting silage or hay because they could eat the remaining
base of pasture which can (not always) be high in mould. Donıt feed any
mouldy feeds, especially to pregnant animals. If grazing silage or hay
paddocks after harvest with safeı animals, remove them as soon as they have
eaten the grass on the edges and the ensilage or hay lying around.
This mould is not new. In maize for silage it can grow in the tips of cobs
(check before harvesting) which adversely affects maize silage, and causes
livestock health problems, especially if maize silage is made without a
mould inhibitor and/or not well compacted.
Long term solutions include aiming for more ³clean² white clover (not more
than 30%) which usually stays greener longer into dry weather. Hill country
clover varieties such as NZ Grasslands Tahora should help because of their
ability to grow for longer into dry periods. Tahora is a dense prostrate
white clover selected from hill country pastures under sheep grazing, so
survives hard grazing more than some upright clovers. It make more nitrogen
than other clovers, especially under low phosphate conditions. See the photo
in the chapter on Clovers.
Dry summer standing deferred grazing pastures can also go mouldy with autumn
rains. Try and finish it before rain or donıt force animals to graze it too
low.
Clovers act as a dillutent, but too much with oestrogen cause their own
problems prior to mating. Using excess nitrogen can suppress clovers and
increase the percentage of grasses and the likelihood of toxicity. High
rates of artificial N can increase ergovaline levels in some perennial
ryegrasses.
Zearalenone levels in pastures, blood and urine can be measured, so farmers
wanting to check should contact their vet (who, however, may not know about
it). The Ruakura charge per group test in 1997 was NZ$76 (1 blood, 1 urine
and 1 grass), or less for more samples, or if combined with their own
batches. Ruakura can hold samples for a few days to batch up and save costs.
Also see Moulds and Silage Moulds.
More is coming.
Best wishes,
Vaughan Jones
Hamilton
Waikato
New Zealand
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