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Wednesday, May 5, 2009

By Department of Primary Industries - 7th May 2009 - Back to News

MINIMISE THE RISK OF NITRATE POISONING

Department of Primary Industries has not yet received any reports of nitrate poisoning this season. However, now that the first rains have occurred and with grass and weeds growing well, it’s worth putting some risk management strategies in place to avoid the impact of this problem on your herd.

In most cases, the cause of nitrate poisoning is relatively simple to understand and it usually involves a combination of the following:

· 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, 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 could cause 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. NOTE: If no plant growth took place for, say a three month period over last summer, there could in fact be as much as 150 to 200 kg nitrogen /ha available for plant growth in the soil now the rains have arrived.

· Stock grazing newly sown pastures which has had vigorous growth and nitrogen becoming available in the soil from excessive organic matter breakdown as a result of the renovation activity.

However, nitrate may be only part of the story!

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

In particular, at this time of the year, many herds have been dried off due to lack of forage and are also not being fed grain – the very energy source they need to metabolise the surplus nitrogen.

Consider cows being fed on a combination of low quality hay (around 7 – 9 per cent CP) or silage (between 10 – 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. These 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 (if you have ever smelt ammonia or smelling-salts, then 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.

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, please contact your nearest DPI dairy extension officer at DPI Maffra on 5147 0800, DPI Ellinbank on 5624 2222 or DPI Leongatha on 5662 9900.

FARMING DIARY

DPI Ellinbank Seminar Series

Topic: Climate Change Impacts on Australian Grazing Systems.

When: Wednesday, May 13, 2009.

Where: Department of Primary Industries Ellinbank, 1301 Hazeldean Road, Ellinbank.

Time: 12:30 pm to 1:30 pm.

Dr Richard Eckard will provide a brief overview of the Whole Farm Systems Analysis and Tools Project and predicted changes in climate for southern Australia. This will be followed by Dr Brendan Cullen, University of Melbourne, who will present the modelling study that addressed the question of the likely impact of projected climate change on current pasture species used across Australia. Everyone welcome.

For more information, please contact DPI Ellinbank on 5624 2222.

Bushfire Recovery Workshop

Topic: Managing Horse Properties

When: Saturday, May 16, 2009

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

Time: 9:00 am to 4:00 pm.

This workshop is aimed at horse property owners who want to learn more about sustainable land management to improve horse health and make better use of soils and pastures. It is open to all landholders, in particular horse owners whose properties have been fire affected.

It is presented by Baw Baw Shire Council and Department of Primary Industries and is supported by Western Port Catchment Landcare Network and Cardinia Environment Coalition.

Refreshments and light lunch will be provided.

For more information, contact Carolyn Ferguson on 5624 2409.

Approaching Next Year at a Lower Milk Price Field Day

When: Wednesday, June 3, 2009.

Where: Mardan Focus Farm at 11:00 am.

Contact: John Mulvany on 0409 935 578.

Fertilising Dairy Pastures

When: Wednesdays, June 17, 24 and July 1.

Where: Department of Primary Industries, Leongatha.

Time: 10.00 am to 2.30 pm.

Contact: David Shambrook on 5662 9913 or 0427 350 928.

Source: http://gippsland.com/

Published by: news@gippsland.com