Basic information from milk is important

A lot of information can be gained from milk without realising it, says Andy Cobner of Penbode Vet Group, Holsworthy, Devon.

 Not only can cell counts of cows be analysed to decide which ones to treat or cull and what new infection rates are, but we can also test for antibodies to many different diseases to assess whether they are a threat to the herd.

With all this information coming at us it’s easy to forget the most basic information can be the most important. The butterfat and protein content of the milk is what pays the bills and the analysis we get from the monthly recording gives us a lot of information about the herd and the individual cow.


More than 400 different fatty acids are present in milk fat. The two most abundant ones are C16:0 and C18:1. These fats are synthesised in the mammary gland and this synthesis can be inhibited when the balance of fatty acids in the rumen is wrong.

When the level of butterfat falls it is a reflection of rumen fermentation and could be looked at as a proxy for rumen health. The health of the cow is reliant on the microbes in the rumen. When the activity of the rumen microbes gets depressed by, for example, too much acid building up, the cow’s health and production will suffer. Most times when the butterfat falls it is the rumen acidity (pH) that needs to be looked at.

When the forage:concentrate ratio in the ration is too low there is too much rapidly fermentable carbohydrate in the rumen which drops the pH and alters the balance and activity of the rumen microbes. The rumen needs long fibre to function which is why you hear talk of the “scratch factor” and “physically effective” fibre content of the ration. You can look at analyses that tell you that there is enough fibre in the diet but this won’t tell you the nature of the fibre which can be crucial.

Milk protein

The protein content of milk is mostly in the form of casein. The milk protein level is important not just because of the payment levels but also because it is recognised as a marker for health, fertility and the likelihood of culling.

Unlike butterfat the protein content of the milk can be difficult to influence. The following factors are known to affect it:

• Dry matter intake

• Rumen stability

• Slow degradation starch sources such as caustic or crimped wheat

• High concentrate feed rate

• Quality of the forages

Fat protein ratio

The fat:protein ratio can be used as an indicator of cow health in two key ways.

First when the ratio of fat to protein is greater than 1.5 it means the cow is potentially short of energy and in danger of developing ketosis. This happens particularly in early lactation. The low energy results in low milk protein and the milk fat rises as the cow’s body fat gets mobilised to meet the shortfall (ie “she’s milking off her back”). When you only look at the overall fat:protein ratio from the bulk tank you can miss this so you have to use milk records to look at the fresh cows.

When the fat:protein ratio is less than one it means the cow is low in fat and could be low in fibre intake. This is an indicator of ruminal acidosis. Picking this up early from the milk records can prevent a serious acidosis problem from developing.