It’s usually in late April and early May that some farmers begin to see a drop in milk fat percentages. The usual reason is low fibre content in the second and third rounds of grazing.

Young, short and leafy grass is high in protein and energy, but is low in fibre and dry matter.

In wet weather, the dry matter drops further. The lack of fibre in the diet and the wet weather can cause low fat percentages and loose dungs. The question is often asked – if this is a problem, what can be done about it?

Looking at cow dung is an important way of managing the diet of dairy cows being fed total mixed rations (TMR). Loose dung with bubbles is a bad sign, indicating sub-acute rumen acidosis (SARA) as a result of a low rumen pH caused by not enough fibre in the diet.

Good practice

Analysing the dung of cows in TMR systems is a good practice as it means changes to the fibre content of the feed can be made quickly, and improvements in cow health and production should follow.

But it’s not the same for cows fed mostly on grass as their rumen environment is different to that of a cow on a TMR. While grass is a forage like grass silage or maize silage, it has lower neutral detergent fibre (NDF) and less effective fibre. It is rapidly digested, meaning that it passes through the rumen quickly. The combination of this and low dry matter means that dungs are often very loose, particularly at this time of year.

Fibre

Often, the advice from some quarters is to introduce fibre to the diet to improve the texture of dung, increase rumen pH and increase milk fat concentrations.

This is fine for cows inside being fed a TMR as it helps to improve rumen function. But research in Ireland and elsewhere has shown that increasing the fibre content of animals being fed grass has no benefit to rumen function or milk production.

Introducing silage, hay or straw to milking cows now will only decrease the quality of the overall diet and reduce dry matter intakes as these high fibre feeds are slow to be digested.

There is no doubt that loose dungs are a nuisance, particularly when milking and low fat percent costs money.

But time, rather than introducing another feed is the best solution.

In summary, loose dungs and low fats are not an indication of health problems in grass-based herds. Nutritionists need to tailor their advice depending on the system of farming.