The NADIS data show that the number of cases of acidosis seen by NADIS vets has increased significantly this winter (2002-2003). The number of cases is likely to remain high until turnout at least, and may increase when the spring-calving season increases, particularly in higher yielding herds.

Like most metabolic diseases it is important to remember that for every cow that shows clinical signs, there will be several more which are affected sub-clinically.

What is acidosis?

Acidosis is said to occur when the pH of the rumen falls to less than 5.5 (normal is 6.5 to 7.0). In many cases the pH can fall even lower. The fall in pH has two effects. Firstly, the rumen stops moving, becoming atonic. This depresses appetite and production. Secondly, the change in acidity changes the rumen flora, with acid-producing bacteria taking over. They produce more acid, making the acidosis worse. The increased acid is then absorbed through the rumen wall, causing metabolic acidosis, which in severe cases can lead to shock and death. The primary cause of acidosis is feeding a high level of rapidly digestible carbohydrate, such as barley and other cereals. Acute acidosis, often resulting in death, is most commonly seen in ‘barley beef’ animals where cattle have obtained access to excess feed. In dairy cattle, a milder form, sub-acute acidosis, is seen as a result of feeding increased concentrates compared to forage. It is this form of the disease that NADIS vets have reported increased numbers of.

CLINICAL SIGNS

1. Reduced milk yield: Initially a moderate decline, eventually a sudden drop
2. Milk fat significantly reduced
3. Body condition and weight loss
4. Reduction in appetite (initially non-forage feeds)
5. Dull, stary coat
6. Reduction in cud-chewing
7. Mild to moderate diarrhoea
8. Temperature usually normal
9. Pulse rate and respiratory rate may rise, particularly if severe