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Addressing the drop in butterfat during early lactation at grass

BEAT THE DROP: Managing and maintaining butterfats during early-mid lactation.

There is much discussion among dairy farmers about low butterfat levels in milk. A decline in butterfat percentages can be common during spring months, when cows are grazing lush grass that is low in fibre and high in oil and sugars — but for some herds, this issue can continue into the summer.

Factors contributing to a decline in butterfat

While there are many factors that influence milk fat, it is believed that a key factor for the occurrence of milk fat depression is an elevated intake of unsaturated fats from young, leafy grass. Unsaturated fats are toxic to rumen bacteria and in order for them to survive they carry out a process call “biohydrogenation” which in turn produces by products that in effect switches off the mammary gland from producing butter fat and thus you get milk fat depression. Data has shown that as little as two grams of these by-products from the rumen can reduce milkfat production by as much as 20%. This effect can be exacerbated in the  presence of a low rumen pH or if rumen health is poor. .

Low rumen pH may also result in other significant consequences for the cow, which has been proven scientifically

  • Reduced fibre digestion.
  • Increased presence of lameness (laminitis).


Recent studies completed in Ireland showed that, during the grazing period, more than 50% of cows experienced low rumen pH and,— but not all of them presented any other symptoms, such as acidosis. 

Here are our top four tips for maintaining or improving butterfat levels at grazing:

1. Concentrate feeding levels

Do not over feed concentrate at milking time (>2/3kg/milking) and make sure that the concentrate contains an adequate level of digestible fibre compared to the sugar and starch content. Examples of good digestible fibre sources would be beet pulp. The use of a forage or straw based supplementary feed can be used to make up for shortfalls in intake, supply adequate fibre levels and spread the volume of concentrate over more feeds.Avoid over-supplementing grass with conserved forage, however, as doing so might increase the butterfat percentage but will also decrease the butterfat yield through reduced milk yield.


2. Grass yield

Achieving grass yields in the range of 1300-1500 (2,800–3,000 NI/UK) kilograms of dry matter (DM) per hectare, especially in the second and third rounds is the target for grazing is the target we should try and reach. Doing so will help increase your protein percentages and milk and butterfat yield. Be wary, however as higher leaf will mean more energy and sugar but this will be low in fibre and higher in fat which could have a negative impact on the butterfat percentage.


3. Forage hygiene

Is your feed or forage mould-free? Mould is a potential indicator of mycotoxins, which can kill rumen bacteria and inhibit fibre digestion, and potentially lower butterfat levels. Since not all moulds are visible, be on the lookout for potential signs of mycotoxin contamination in your cows. This can be especially important as we are using less volume of feeds as cows go to grass. Do you know what these symptoms look like? Visit for more information.


4. Feed additives

Does your diet include a live yeast? Alltech’s YEA-SACC®, the most widely researched live yeast culture on the market, promotes rumen stability, helping cows avoid variations in rumen pH that could interfere with dry matter intake, fibre digestion and butterfat production. Yea-Sacc works by removing air/oxygen from the rumen  and increasing the presence  of fibre-digesting bacteria. This helps reduce acidity in the rumen and increase the pH which can maintain or increase butterfat levels. This is all about getting the rumen to be healthy, working better and more efficiently and so getting better utilisation of feed and so more output.

Research conducted in Ireland at University College Dublin’s Lyons Farm has illustrated that the specific live yeast in Yea-Sacc can help increase rumen pH and reduce the duration of periods of low rumen pH during the day. Furthermore, cows fed Yea-Sacc had significantly less body fat loss and had a better energy balance.

Figure 1. Effect of Yea-Sacc supplementation or control on rumen pH (P<0.01)

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There are many factors that can cause milk fat drop during the e grazing season. While some of these issues are unavoidable as we focus cows on eating large quantities of high-quality grass, what we do know is that these milk fat depressions are exacerbated if we do not have good rumen health and so improving rumen pH, overall rumen function and increasing fibre digestion is a central part of this challenge. To help beat the drop, ensure that Yea-Sacc is included in your feed.