Nutritional Issues

A well-balanced and consistent diet is the key to achieving sound rumen health in dairy cows and high milk productivity.

Ruminal acidosis

Ruminal acidosis is caused when the acidic balance in a cow's rumen is upset, resulting in weight loss and a drop in milk production. It is especially common in dairy cattle fed on high quality pasture and grain. Maintaining a stable rumen environment will reduce the risk of acidosis and ensure cows have a better chance of achieving their full milk production potential.

Ruminal acidosis can be caused by the sudden ingestion of large amounts of starch-based concentrates or other rapidly fermentable carbohydrates. This can take place if cattle access areas where this type of feed is stored or when cows are fed poorly mixed rations with uneven feed distribution.

Treatment of ruminal acidosis depends on the severity. Cows with mild cases should be removed from the offending feed source, fed good quality fibre and given an oral buffer such as magnesium oxide. Severely affected animals may require intravenous fluid therapy and emergency surgery to empty the rumen contents.

Milk fat depression

Milk fat depression (MFD) is a drop in the milk fat percentage and milk fat yield without impacting the milk protein component. The condition is associated with subtle changes in the cow's rumen.

MFD is tracked on milk fat percentage and is typically observed between winter and early spring when cows are feeding on lush pasture or eating high grain and low roughage. The onset of MFD can be avoided by feeding cows a source of grain or concentrate with slow fermentable starch (e.g. maize grain) to help the rumen and boost digestibility in the rest of the gut in conjunction with good grazing management.

It takes between 10 to 14 days to reverse MFD following a diet adjustment. However, positive changes should start to occur after seven days. If there is no change after 10 to 14 days, further investigation and adjustment may be required.

Changing diets

Most diet-related conditions in cows occur due to sudden changes in grain feeding practices, which can disrupt healthy rumen function, feed intake and general health. A lack of monitoring how a cow has responded to such feeding changes can also miss early warning signs that something is wrong. It is recommended substantial dietary changes are made gradually to allow the cow’s rumen adequate time to adapt.

While concentrates or grains are usually the main culprit of diet-related issues, it is important to remember that rumen microbes are actually very sensitive to sudden changes in all diet components. Many Australian farmers will have noticed a dramatic drop in milk production when the forage base suddenly changes from grazed pasture to silage as happens in many regions in late spring.

Key aspects to consider when changing diets include:

• Change over cows gradually onto new feed over seven to 14 days.
• Rumen microbes need time to adapt to new feed sources.
• Monitor animal responses to other risk factors such as any toxic components in feed.
• Equal access to feed for each cow is essential.
• It is not about what is fed, it is about what cows eat.
• Introducing palatable, low-fibre feeds to the diet is high-risk.