It’s that time of the year again when farmers start to notice erratic butterfat levels in milk.

Some farmers notice fat levels dropping and rising by up to 0.5% at individual collections.

Low butterfat levels are a cause of concern, not just because it costs money, but also because it could signify some other issue going on with the cow.

So what’s the cause and what’s the cure? The bad news is there are no straight answers to these questions, particularly when it comes to grazing livestock.

Genetic potential for butterfat definitely has a role to play but it doesn’t explain why butterfat can fluctuate so much at herd level.

A big problem is that many nutritionists and sales reps confuse butterfat issues in herds fed a total mixed ration (TMR) with herds fed primarily grazed grass. In reality, these are different issues and the fix for one may not be the fix for the other.

One such “fix” that is often put out there is to feed more fibre to dairy cows such as straw or include a special additive in the feed such as protected fats, acid buffer or yeasts, etc.

These additives are costly to include adding €20/t to €30/t more to the cost of a dairy ration and are required to be fed at a minimum of 3kg per day in order to be present in sufficient volumes to achieve the stated claims.

Teagasc researcher Michael Dineen is running a large study on this topic at present. Together with PhD student Chris Heffernan, they are looking at the causes of milk fat drop with 29 commercial dairy farms enrolled in the study. Grass and meal samples for chemical analysis along with milk samples are collected on these farms every three weeks.

This project is now in its second year of data collection with one more year to go.

Alongside this, the researchers with the help of farm manager Ricki Fitzgerald, are running controlled experiments at the Dairygold research farm at Kilworth.

Preliminary results are available from last year’s study looking at the impact of concentrate feeding levels and concentrate ingredients on butterfat percent.

The ingredients were protected fat and sodium hydroxide treated straw pellets.

There were 80 cows on the experiment, which ran from April to July 2021. Cows were randomly assigned to one of five treatments:

  • Grass only.
  • Grass and 2kg meal.
  • Grass and 4kg meal.
  • Grass and 4kg meal with straw pallets.
  • Grass and 4kg meal with protected fat.
  • Cows were left to acclimatise to each treatment for one week with data collected over the following 12 weeks.

    All cows were grazed together, getting 24 to 36 hours per paddock and were moved on to the next paddock when post-grazing sward height was between 4cm and 4.5cm.

    While feeding more concentrates increased the total milk yield and kilos of fat produced, the amount of concentrates and the type of ingredients it contained had no significant effect on butterfat percent in the milk.

    However, there was some numerical differences observed, with the cows on protected fat producing an additional 1.4kg of milk per day compared to the cows on the 4kg of meal with no special additives.

    There was also no significant difference in bodyweight or body condition score between the treatments.


    The fact that there was no significant difference between the treatments with regard to butterfat percent is a result in itself.

    Straw and rumen protected fats are just two additives targeted at fixing this butterfat drop problem.

    There are also acid buffers and yeasts on the market which the researchers should also test.

    This is important research as farmers are spending thousands per year on products that, if these results are anything to go by, make no difference to butterfat percent.