Sponsored by

What does a drop in milk butterfat during April and May mean for your herd and your profits?


The lush, leafy swards typically seen at this time of year are great for milk production and milk proteins.

But this highly-digestible grazed grass is generally rich in rapidly-fermented sugars and low in structural fibre content and can lower rumen pH and promote a condition called sub-acute rumen acidosis (SARA). This significantly impacts on rumen efficiency, herd performance and fertility. What’s more, SARA can have a significant impact on milk solids yield and consequently milk price.

It can often go undetected but there are some simple warning signs that you can look out for that can indicate a potential problem with SARA in your herd at this time of year.

Look at dung!

Is dung loose, with gas bubbles in it? This can suggest excess production of acids in the rumen due to the rapid fermentation of grass resulting in SARA (also check protein and magnesium levels and for liver fluke).

Are there undigested fibre particles in the dung? This can suggest reduced rumen digestion due to lowered pH (also check for energy and protein content relative to milk yield and stage of lactation, as low protein can also cause this). Also look for cud balls in collecting yards at milking, which are an indicator of poor rumen function.

Assess rumen fill

Look at rumen fill three to four hours after morning milking - poor rumen fill can be caused by reduced dry matter (DM) intake due to acidic conditions in the rumen (also check for low DM grass and high protein grass as this can also cause poor rumen fill).

Are cows cudding well?

Are cows lying down ruminating? More than 65pc of the herd should be ruminating two to three hours after milking unless they are drinking or actively grazing. Drool and saliva should be observed around the muzzle, with greater than 60 chews per cud where strong rumination is evident.

Are cows losing weight?

Minimising weight loss for cows in early lactation is an absolute priority in order to ensure cows are in optimum body condition score at the start of the breeding season. Maximising dry matter intake is crucial from this perspective and issues like SARA and poor rumen function should be avoided to ensure that the rumen is drawing sufficient nutrition from the diet to support milk solids production and minimise condition loss. Pay particular attention to cows who have calved during the previous six weeks.

What’s happening with milk quality?

If you notice a 0.3pc to 0.5pc drop in butterfat over a week or a 0.3pc drop in protein in milk, then this could indicate SARA. If milk yields drop by around two to three litres per cow per day over the course of a week then this can also indicate acidosis problems.

Look at individual milk recording data - if more than 10pc of the herd has a higher milk protein than milk fat percentage, this indicates a potential problem with SARA. Averages can be misleading. It is worth noting that relatively high oil levels in grazed grass can also contribute to butterfat crashes during the grazing season and this is why it is worth working through the aforementioned points to ensure that SARA is the root of the issue.

The below table illustrates the effect on profitability of a sharp drop in butterfat levels on a 100-cow herd over the course of one month.


Research has shown that you can reduce the risk of SARA in your herd by adding Actisaf Sc 47 live yeast to your compound feed. Farmers can rest assured that if SARA does become an issue, Actisaf will stablise rumen function and pH, minimising negative impacts on performance and cow comfort.

Even when SARA isn’t a problem, Actisaf significantly improves rumen efficiency, leading to increased digestion, better utilisation of grass and increased milk solids yield. Phileo UK & Ireland recommend that Actisaf is included at a minimum rate of 1-2kg per ton of compound feed depending on the compound feed rate, which will cost approximately €10-20 per ton.

You can find out more about SARA at grass and how Actisaf can help by reading their guide on how to reduce the risk of SARA at grass. Learn how one grass-based dairy farmer has seen the benefits of using Actisaf at grass here.