Why lush, leafy grass swards can hit dairy cow performance

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 SARA – sub-acute rumen acidosis.

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)
  • 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.
Normal dung, indicative of normal rumen fermentation pattern
Normal dung, indicative of normal rumen
fermentation pattern
Gas bubbles and loose dung, indicative of excess lactic acid production in the rumen
Gas bubbles and loose dung, indicative of excess lactic acid production in the rumen

Assess rumen fill

  • Are cows cudding well? Are cows lying down ruminating? More than 65% of the herd should be ruminating 2-3 hours after milking unless they are drinking or actively grazing. Drool and saliva should be observed around the muzzle, with greater than 65 chews per cud where strong rumination is evident.
  • Are cows losing weight? Excessive weight loss could be as a result of sub-optimal rumen function as a result of SARA causing a drop in dry matter intakes. Excess body weight loss predisposes cows to several disorders including lameness, ketosis, milk fever, fatty liver and poor fertility.
  • What’s happening with milk quality? Milk quality and yield – if you notice a 0.3%-0.5% drop in butterfat over a week or a 0.3% drop in protein then this could indicate SARA. If milk yields drop by around 2-3 litres/cow/day over the course of a week then this can also indicate acidosis problems. Look at individual milk recording data – If more than 10% of the herd has a higher milk protein than milk fat percentage this indicates a potential problem with SARA. Averages can be misleading!


If you suspect SARA in your herd then research has shown that you can reduce the risk by adding Actisaf Sc 47 live yeast to your compound feed.

Actisaf significantly improves rumen efficiency, leading to increased digestion and utilisation of grass, and promotes a stabilising effect on rumen pH, reducing the threat of SARA.

Farmers View

Adrian O’Driscoll has a real focus on maximising the amount of milk solids produced from grazed grass, while also ensuring he meets the nutritional requirements of his herd while grazing.

“I am happy to feed my cows in order to optimise milk solids yield, minimise body condition loss and promote good fertility, and I try to combine this with effective utilisation of my grassland swards.”

Adrian runs a herd of 70 cows near Drinagh in County Cork, which is block spring calving.

sara 1 adrian-odriscoll

This year he started calving in late January and had 55 cows calved in the first three weeks, with those cows averaging 30L at 4.16% fat and 3.48% protein after three weeks.

He aims for a 16-week breeding period each year, with the majority calving within 12 weeks, and this year 90% calved within an eight-week block, so he is pretty comfortable with cow fertility performance.

In 2015, Adrian’s herd achieved milk quality of 4.20% fat and 3.6% protein, with cows peaking at 32.5L/day – more than 500kg of milk solids a year, with an expectation of higher yields this year based on performance so far.

Cow Diet

Dry cows are fed a ration comprising grass silage, straw and minerals, with any cows that look a bit thin getting 1kg/head/day of a dry cow ration.

Whilst they are housed before turn-out, early lactation milking cows are fed a TMR comprising 73 DMD grass silage, 12kg of fodder beet, 2kg of a rolled barley/maize meal mix, along with 6kg of an 18% crude protein nut through the parlour.

When cows go out to grass, usually in early March, Adrian continues to supplement them with 4-5kg/day of a nut through the parlour once they are grazing full time, although this reduces to a 14 per cent crude protein nut.

dairy farmers milk prices EU

“I think it is important to keep supplementing cows at grass to maintain performance and I definitely get a yield response to the feed I give through the parlour,” Adrian explained.

“In wet weather, I will increase the parlour feed rates to ensure adequate energy intake to sustain performance. We only average around 1t of feed/cow/year, so we are not feeding a lot, but the benefits far outweigh the costs in my opinion.”

Issues with milk solids

One issue that Adrian has seen when grazing in the past is variable milk fat and protein levels, as well as loose dung, particularly when grass is lush and leafy.

“I was advised to try adding Actisaf live yeast to our parlour nut to help address these issues,” Adrian said, “and I’ve been really pleased with the results.”

“Milk solids remain much more consistent throughout the grazing season. I’ve also noticed cows are much more content at grass now, with improved cudding rates, whereas before at times they were not as settled as I would like, even in good swards of grass, something which would go hand in hand with milk constituents dropping.”

sara 4

Overall, Adrian aims to maximise the amount of milk solids he produces from grazed grass and aims to complement this with strategic feeding of nuts through the parlour and buffer feeding when required.

“Our approach is to maximise the utilisation of grazed grass from the grazing platform while also endeavouring to promote good herd health and fertility.

“Feeding Actisaf through the parlour nuts has contributed to this, as I feel it helps keep the cows performing consistently during the grazing season.”

Click here for more information on how to reduce the risks of SARA at grass