Making the most of high quality grazed grass and efficiently converting it into milk solids is critical for any profitable dairy enterprise.

Many farmers will already be getting cows out grazing by day, with a view to getting the herd out full time as soon as ground conditions and growth rates allow.

Here are some top tips to making the best of spring grazing while also highlighting some of the factors that can cause issues.


1. Gradual turnout

Turning cows out to grass creates a substantial change in diet for the cow. It takes around three weeks for the bugs in the rumen to adapt to significant diet changes such as this, so it is important to manage the transition to grazing gradually.

Even a few hours of on/off grazing by day, when weather conditions allow, will mean that the rumen bugs can adapt to fresh grass.

Cows should be able to consume 5kg DM in approximately three hours in suitable swards and weather conditions.

2. Dry Matter Intakes

The moisture content of grass can vary significantly in spring, typically from 80-90% moisture depending on the weather, and this can have a major impact on dry matter intakes.

For every 1kg of fresh grass a cow eats at 15% DM she will only be consuming 150 grams of dry matter so this means that a cow estimated to consume 15kg of grass dry matter needs to eat 100kg of fresh grass.

Remember, there is no energy in the water/moisture content of grass, therefore, it is important that you don’t overestimate what dry matter intake a cow can take from grazing, or performance and fertility will be compromised.

Video: Managing turnout to grass

3. Excess crude protein

Lush, leafy spring grass can often have a crude protein content in excess of 250g/kg DM, particularly after fertiliser application, and this is mainly rumen degradable protein (RDP).

Rumen microbes are unable to utilise this much protein from high grass intakes, particularly if there is a shortage of fermentable energy available to them, and so excess RDP is broken down into ammonia in the rumen, and then absorbed into the blood stream and converted to urea in the liver.

Elevated blood urea nitrogen levels (BUN) from excessive crude protein in the diet can increase body condition score loss, reduce fertility and impact on hoof health.

water troughs dairy

4. Buffer feeding

During the transition to grazing when grass is gradually being built up in the diet, high DMD forages such as maize and/or grass silage should be fed while cows are initially in by night and out by day, to ensure dry matter intake is maximised.

Only forages with a high energy content and digestibility should be fed, so that cows are supplemented to their required energy requirements and grazed grass is not substituted.

Starch-based forages such as maize silage are a great combination with grass, as the use of nitrogen in the rumen is enhanced and microbial protein synthesis is increased due to the fermentable energy being supplied by the maize starch.

This will help to maintain milk constituents and protein, in particular.

Buffer feeding should also be strategically implemented during periods of wet weather throughout the grazing season when required grass dry matter intakes cannot be maintained due to low grass dry matters.

In order to maximise the use of grass during wet weather, buffer feed should be fed after cows have grazed and ideally a few hours before milking.

5. Highly digestible grass swards can challenge rumen function

Lush spring grass tends to have a high proportion of leaf to stem, resulting in low structural fibre levels in the overall diet.

This lack of ‘scratch factor’ can impact on cudding rates and saliva production, further compromising rumen function.

While the nutrient analysis of grass can vary wildly, this lack of structural fibre can be accompanied by high sugar levels – often more than 18% during sunny, dry weather.

High sugar levels are great for rumen fermentation, promoting good milk proteins and strong yield, but when supplied in excess in combination with low structural fibre they can challenge rumen function, leading to sub-acute rumen acidosis (SARA).

Consequently, butterfat % and milk protein % can be compromised as a result of the change in rumen fermentation, whilst prolonged challenges can impact on fertility.

High levels of unsaturated fatty acids in spring grass can also cause butterfat % to be reduced, so lower butterfat doesn’t always mean SARA is a problem, however.


6. Compound feeding

It is important that compound feed, fed through the parlour, tops up the dry matter that grass and forages do not supply in order to match the energy requirements for a given yield.

It is also important that the nutrient content of the compound feed balances that of the grass to optimise rumen fermentation and maximise performance.

Aim for a feed that has around 14-16% crude protein, a high digestible fibre content (such as sugar beet pulp and soya hulls), a balanced source of cereals including maize and barley and a source of bypass protein.

It should also contain minerals that grass is deficient in, for example magnesium, which as well as having a vital role from a grass tetany prevention point of view, can lead to poor rumen muscular function, and hence sub-optimal rumen function, if deficient.

7. Monitor what the cows are telling you

It is advisable to assess rumen fill two-to-three hours after milking to determine whether adequate grass has been allocated.

  • Monitor cudding rate – you are looking for more than 65% of the herd to be lying down chewing the cud 2-3 hours after milking.
  • Check dung consistency – loose, bubbly dung with undigested fibre in it is indicative of poor rumen function, as is the presence of cud balls in collecting yards or cubicles.
  • Monitor condition – cows losing body condition can point to insufficient feed intake, a possible metabolic disorder, health issue or sub-optimal rumen function.
Loose, bubbly dung, with undigested fibre in it is indicative of poor rumen function

Loose, bubbly dung, with undigested fibre in it is indicative of poor rumen function

9. Milk quality

Monitor bulk tank milk collections for average yields and constituents. A fall in butterfat or protein of 0.3% or greater in one week is a warning sign for poor rumen function and the occurrence of SARA.

It is also useful to keep an eye on the butterfat to protein ratio to ensure this falls within the optimum range of circa 1.2:1.

Ahead of this year’s grazing season it is worth looking back at last year’s individual milk records for cows at different time points during the spring grazing season to see what percentage of the herd had butterfat to protein ratios outside of the optimum range to identify bottlenecks ahead of this season.

This should be an ongoing process this spring after each milk recording, as it is more accurate than looking at bulk tank records which is a more general initial indicator.

10. Feed Actisaf live yeast

Adding Actisaf live yeast to your cows’ ration will reduce setbacks in performance at turnout by helping the rumen bugs adjust to grazed grass and improving rumen function.

Actisaf also reduces the risk of SARA, both at turnout and throughout the grazing period.

Actisaf helps to stabilise rumen function and promotes milk solids and milk yield. It should be included at a recommended rate of 1kg/tonne of grazing compound, assuming a feed rate of 4-6kg/compound/cow/day.

What do farmers think?

John Power farms in partnership with his parents, Maurice and Helena, at Lismateigue, Knocktopher, Co. Kilkenny.

Together they run a spring-calving dairy enterprise alongside a successful dairy calf-to-beef operation. Cows typically start to calve in mid January and John aims for a compact calving period.

John Power

John Power pictured on his farm in Co. Kilkenny

Grazed grass forms a big proportion of the herd’s ration and John aims to include grass into the cows’ diet early in the spring.

Last spring, John added Actisaf live yeast to his cow diets and and noticed that it helped improve milk solids production while also significantly improving rumen efficiency.

For more on John Power’s farm Click here

Sean Cleere milks around 200 cows with his wife, Joanne, near Templetuohy in Co. Tipperary and in previous years his herd has experienced sub-acute acidosis.

He runs a spring calving herd with the aim being to maximise the utilisation and conversion of grass into milk solids. He starts calving at the end of January and cows typically go out in early March.


Sean Cleere pictured on his farm

Sean started feeding Actisaf in May 2015 and noticed benefits straight away.

“I was a bit sceptical but I noticed a difference in dung consistency when the Actisaf went in initially, so that made me think it was doing some good with regards to digestion in the rumen,” he explained.

“We have also historically seen milk butterfat % dip during spring grazing as well, so the impact that Actisaf can have on milk quality was something that interested me.”

To read Sean Cleere’s full story Click here