Tackling hidden cost of acidosis

26 February 1999

Tackling hidden cost of acidosis

ACIDOSIS in dairy cows is expensive, causes many hidden losses, often goes unnoticed, and in most cases could be avoided by promoting good rumen function.

Speaking at a Keenan meeting in Cheshire, US vet Bill Prokrop said that many acidosis cases were sub-clinical and dairymen often only saw the extreme cases.

With sub-clinical cases, herds were suffering losses that they were unaware of because it didnt involve writing a cheque, he said. He believed acidosis was costing US dairy producers £140/cow, but admitted UK diets appeared less likely to cause acidosis.

Many producers are willing to accept a certain level of disease such as acidosis or milk fever, but ignore increased risks of other metabolic disorders, mastitis and lameness.

"When you understand these hidden costs of a disease, you realise that you dont need to ask your vet for better treatments, but how to achieve fewer cases of disease."

Lowering sub-clinical acidosis means feeding to maintain a healthy rumen. Optimum rumen health both depends on and helps maximise dry matter (DM) intake. After providing a cows maintenance requirements this dictates yield and, therefore, profit.

Acidosis risks are increased when cow diets contain conserved forage and concentrates which are far more acidic than grass, said Keenan nutritionist Tony Hall

Grass silage, maize silage, maize distillers and maize gluten are acidic, as are most concentrates – except sugar beet pulp.

"These acidic diets require cows to chew and cud more to produce enough saliva, so diets must provide adequate structural fibre," added Mr Hall.

Long straw can be used to increase fibre length, but too much will lower DM intakes. Intakes are also lowered when there is too little fibre in a ration, such as when straw is finely ground.

Diets of the same chemical composition can have different values for structural fibre, depending on how finely they are chopped. When they are too low in structural fibre – too finely chopped – or too high in fermentable carbohydrate they can cause sub-clinical acidosis.

When feeds are over-chopped or over-mixed they dont encourage high DM intakes. To ensure good DM intakes, cows need enough long material – this shouldnt shake through a 18.8mm (0.75in) sieve. Dr Prokop suggests that this material should make up 15-20% of a ration weight.

In addition, a further proportion of that which goes through the first sieve shouldnt go through a 8.8mm (0.31in) sieve. The contents of both sieves should add up to 50% of the ration by weight.

This system of measuring particle size was developed in the US by Penn State University. It aims to ensure enough fibre is fed to promote chewing, encourage saliva production and, therefore, neutralise rumen acid, said Mr Hall.

Ration fibre content may be increased by tactical feeding of hay or straw. However, a better option is not to overchop silage, so that it doesnt fall through the 18.8mm (0.75in) sieve.


&#8226 Dont overchop silage.

&#8226 Encourage high intakes.

&#8226 Monitor disease levels.

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