Latest News

• Add My News • Search Old News

Gippsland › Latest news › Department of Primary Industries

AG News

Nitrate Poisoning Causing Stock Losses In Gippsland; Farming Diary

By Department of Primary Industries - 11th September 2009 - Back to News

NITRATE POISONING CAUSING STOCK LOSSES IN GIPPSLAND

Over the past week in Gippsland, some cattle deaths have been attributed to nitrate poisoning highlighting the risk of feeding pasture, conserved fodder or crops that may contain excessive amounts of nitrate.

What are the signs of nitrate poisoning?

Nitrate poisoning occurs very quickly. Symptoms are often not observed and animals are found dead.

If symptoms are seen, affected animals stand apart, have an unsteady gait, have rapid and shallow breathing and eventually collapse. The whites of the eyes and membranes around genitalia, the mouth and nostrils will appear initially bluish in colour, and then muddy brown.

Following exposure to abnormal nitrates or nitrites, a cow that survives may abort her calf because it died of oxygen starvation.

Is treatment available for nitrate poisoning?

Treatment is not usually possible because death often occurs so suddenly. However, if cattle are observed in time intravenous administration of methylene blue can save them.

The remaining herd in a ‘problem paddock’ should be moved carefully and as quickly as possible.

What causes nitrate poisoning?

Nitrate poisoning occurs when ruminants (including cattle and sheep) eat crops or fodder with high nitrate levels.

Its cause, in most cases, is relatively simple to understand and usually involves a combination of the following reasons:

· Hungry and unadapted cows introduced to possible ‘problem paddocks’.

· Capeweed, forage oats, annual ryegrass, short rotation ryegrass, young cereal crops, or volunteer Brassicas in the paddock.

· Last autumn for example, there were some reports of stock deaths on perennial ryegrass; but this is normally not the case as mature perennial ryegrass pastures are not known to accumulate toxic levels of nitrate. If this does happen, you will need to look for what else is in the pasture that may have caused the nitrate poisoning.

· Either grazing too soon after heavy applications of nitrogen fertiliser (greater than about 50 kg N/ha) or after a drought when the ‘natural soil nitrogen’ has not been extracted from the soil for the summer.

· In summer, if no plant growth takes place for up to three months, there can be as much as 150 to 200 kg nitrogen per hectare available for plant growth in the soil when the rains do arrive.

· Stock grazing newly sown pastures that has had vigorous growth with nitrogen becoming available in the soil from excessive organic matter breakdown because of ‘renovation’ activity.

Often where nitrate levels are high, the total crude protein content of the diet is also high. Annual ryegrass pastures can commonly contain as much as 35 per cent crude protein (CP) at this time of year.

Given that a lactating dairy cow only needs 16 to 18 per cent CP in her diet; this places a huge energy stress on the cow to excrete surplus protein.

If fed with a low protein feed such as grain, some surplus nitrogen can be ‘mopped up’. Obviously, this will not occur with ‘dry cow feeding’ and this presents a higher risk especially on a high pasture diet.

For example, cows being fed on a combination of low quality hay (around 7 to 9 per cent CP) or silage (between 10 to 12 per cent CP). If these cows are then turned out early onto the first grazing of an annual ryegrass or cereal crop, they are suddenly exposed to CP levels around 35 per cent, together with high nitrate levels.

Normally cows can regulate their intake of excess protein, by cutting back on intake when their blood pH signals too much ammonia in the rumen. The problem is that these starved cows gorge themselves on the fresh grass and by the time the signals arrive at the brain, there is still three quarters of the high nitrate forage in the rumen to digest.

Commonly cows subjected to this sudden change will either bloat (a free gas bloat with a strong ammonia smell), or start showing nervous symptoms associated with excess ammonia in the blood (not measured as blood urea).

Some early warming signs are a strong ammonia smell in the dairy (excess nitrogen in the urine), urine scaling in the grass, cows trying to kick their bellies or generally looking rough.

Affected cows will commonly pick at a bale of rubbish hay or dead grass on the roadside in an attempt to get their rumen going again (ever smelled ammonia or smelling-salts – imagine what it does to the rumen wall?). What these cows are looking for is a ‘scratch-factor’ to get the rumen turning over again.

The greatest concern from excess protein may not be a large number of dead cows (as this is not as common), but the number of un-thrifty cows (sad cow syndrome), thus producing less milk or losing weight through reduced intake.

Is poisoning preventable?

There are number of tips for surviving both nitrate and ammonia problems:

· Avoid a rapid change in diet quality, for example moving dry cows from perennial ryegrass to a cereal crop (or even annual ryegrass at certain times of the year);

· Never give starved, unadapted or dry cows, unrestricted access to recently or highly nitrogen-fertilised pastures;

· Grain fed cows are generally less susceptible, as rumen microbes have more energy to adapt to the new diet, plus the cow has more energy to metabolise the excess protein;

· Do not graze pastures until about 18 to 21 days after nitrogen fertilisation.

· Do not apply more than 50 kg nitrogen per hectare in a single application, particularly after the autumn break (and especially following a long dry summer) and in spring;

· An ammonia smell in the dairy or urine scalding of the grass is a sure sign of excess protein in the diet;

· Cows that are suffering as a result of excess nitrogen in their diet tend to select for lower quality roughage. A bale of ‘rubbish hay’ in the corner of the paddock can be used as an indicator of nitrogen stress.

· Spray to kill cape weed. The spray and graze method can be a reasonably effective technique for reducing broad-leaved weeds and is cheaper, but the sprays used increase the palatability of the weeds and so increases intake of their leaves which are highly concentrated with nitrogen. This is exacerbated if the weeds are growing in annual or short rotation ryegrass pastures.

For more information on animal health or pasture management, please contact your nearest DPI office at Maffra on (03) 5147 0800, Ellinbank on (03) 5624 2222 or Leongatha on (03) 5662 9900.

FARMING DIARY

Irrigation Farm Walk

A new automatic weather station has been installed at the Macalister Demonstration Farm to help farmers better schedule their irrigation. The farm walk includes a visit to the weather station and discussion on how to access and use the information.

When: Thursday, September 3, 2009

Where: Macalister Demonstration Farm

Time: 10:30 am to 12:00 noon.

Morning tea available from 10:00 am onwards.

For more information, please contact Brendan Stary at DPI Maffra on (03) 5147 0840.

Adaptive Forage Planning

Department of Primary Industries (DPI) will be running two Adaptive Forage Planning Discussion Days in the Rosedale area on Wednesday, September 9; and in the Yarram area on Thursday, September 10 respectively.

As Gippsland continues to experience seasonal variability, DPI is currently comparing a range of crops that can be utilised under these conditions in the future.

Both days are designed for dairy farmers, graziers, croppers and interested service providers to examine various crops and discuss their potential for both dairy farmers and forage producers.

For more information, please contact Frank Mickan on (03) 5624 2259 or Greg O’Brien on 5624 2288.

Pasture and Grazing after Bushfire

When: Saturday, September 12, 2009

Where: Labertouche Hall, Cnr Labertouche and Forest Road, Labertouche

Time: 9:30 am to 12:30 pm.

Department of Primary Industries’ Fiona Baker will present a Pasture and Grazing workshop providing practical advice on how to establish and manage productive pastures to meet livestock grazing and fodder needs.

The workshop will focus on soil testing, selection of pasture species, fertilisers, sowing techniques and rotational grazing systems. It will also include pasture inspections of various paddocks re-sown since the Black Saturday fires.

All landholders are welcome, in particular those whose properties have been fire affected.

For more information, contact Carolyn Ferguson on (03) 5624 2409.

Source: http://gippsland.com/

Published by: news@gippsland.com