Are you putting your cows at risk of acidosis?
With rising prices of fibre sources, such as hay, it may be tempting to reduce the fibre content of the diet. However, doing so may lead to losses in milk production through acidosis. If you have limited fibre available, it will be important to plan the rate of feeding to ensure you still have enough to feed a balanced diet in late winter/early spring.
Effective fibre is important in maintaining rumen health as it promotes the cud-chewing, saliva production and rumen contractions that assist with maintaining a healthy rumen environment. Cow's saliva is important as it contains naturally occurring buffers, including bicarbonate, that neutralise acids produced during digestion to assist with the maintenance of a suitable rumen pH. Without sufficient fibre in the diet, saliva production is not sufficient to maintain a stable rumen pH and the rumen becomes more acidic.
Some feeds require more chewing and result in more saliva production than others, which is related to the amount of fibre they contain. Fibre is the structural carbohydrate component of the plant that allows the plant to stand up. It is located within the cell wall and is made up of three main components: hemicellulose, cellulose and lignin. These components within a feed are estimated, via chemical testing, as Neutral Detergent Fibre (NDF). Cows require a diet containing 30-40 per cent NDF within their daily dry matter intake. Of this 75 per cent needs to have a fibre length greater than 1.5 centimetres.
The amount of acid production that needs to be neutralised varies with diet. If cows consume sufficient amounts of highly digestible feeds, such as grain and actively growing pastures, rumen pH drops. This results in reduced populations of fibre-utilising bacteria and increased proliferation of acid-producing bacteria. This leads to increased production of acid and therefore a reduced rumen pH. The rumen's natural buffering capacity cannot keep up with the production of acids and the pH continues to decline. This may lead to acidosis.
Cows with rumen pH between 5.2 – 5.6 have sub-clinical acidosis. These cows may not appear to be sick, although feed intake and milk production will be reduced. Animals with a rumen pH below 5.2 will be suffering from acidosis. These animals will be noticeably sick with reduced milk production, reduced appetite and scouring. This may result in downer cow syndrome and ultimately death.
There are some things you can do to check if you are feeding enough fibre. These include:
Is there any grain or concentrate left in the bails?
If bails have over 10 per cent of feed left behind the accuracy should be checked. To do this, check the accuracy of 10-20 individual feeders. If they are dispensing the right amount consider reducing how much you feed. If one bail has over 50 per cent left some cows have substantially reduced appetites. Check for cud chewing and manure consistency. Minimise the exposure to infectious organisms to prevent infectious scours.
Is there sufficient effective fibre in the diet?
The cows need 30-40 per cent of their diet to be NDF and of that, 75 per cent to be effective fibre. Some feeds, for example palm kernel extract (PKE), have a high NDF percentage but a low effective fibre content resulting from a small particle size. Alternative fibre sources may be used to extend hay stores, but they cannot be used as the sole source of fibre.
What is the vat telling us?
The fibre and energy content of the diet contribute to milk fat percentage. A reduced fat test may indicate acidosis, especially if the fat test falls below the protein test.
What is happening in the paddock?
Observe the behaviour of cows after they have eaten. This is likely to be two hours after milking.
- Are the cows chewing their cud?
At least half of sitting cows should be chewing their cud. If there are less than 50 per cent of the sitting herd chewing their cud, this indicates insufficient fibre in the diet and it should be increased.
- Are there lame cows?
Laminitis can be a sign of acidosis. Your vet will be required to identify if the lameness is a result of laminitis.
- Is the manure consistency correct?
If manure has a porridge-like consistency, forming a soft pile 40-50 millimetres high, and making a plopping sound when it hits a concrete floor, then the diet has enough fibre. Manure that is of a watery consistency and light in colour indicates insufficient fibre in the diet. A loose dark manure is more likely to be due to the amount of pasture in the diet and is still safe if other indicators are OK.
In summary, insufficient fibre in the diet can lead to acidosis. Cows with acidosis have reduced feed intake, decreased milk production and scours. There are also other indicators that can be observed in the dairy and paddock that can signal acidosis. It is important to maintain adequate fibre levels in the diet and ensure that 75 per cent of that fibre is effective in order to minimise the risk of acidosis. Plan your hay and silage feeding so that you don't run out in late winter, as hay is expensive and difficult to source at present.