Advice on measuring milk from forage in grass-based herds

Farmers Weekly’s recent dairy sustainability survey revealed the average herd is producing 3,258 litres from forage.

But is this metric still a reliable measure of efficiency in a grass-based business?

Flexibility, adaptability and nerves of steel are needed to really make milk from grazed grass work.

The key is to set up infrastructure and management to maximise utilisation of grass grown on-farm, then have the confidence to pull concentrates out of the diet.

See also: What makes a sustainable dairy farm – survey results

The difficulty is in choosing which KPI to use to track progress.

Metrics to measure success (or lack of) are useful, but it is important to know their limitations and use them accordingly, says LIC farm business consultant Sean Chubb.

They must correlate with efficiency and profit.

The traditional milk from forage (MFF) figure is a back calculation based on energy-corrected litres of milk, plus a cow’s maintenance requirements (see “Milk from forage in litres 2024”).

In a pasture-based herd, this may mean using a smaller cow type, but it must factor in the amount of walking to grass that is done, he points out.

According to DairyNZ figures, for every 1km walked on the flat, a cow requires 2MJ of metabolisable energy (ME).

On rolling land, this rises to 3MJ of ME, and on steep land it is 6MJ, says Sean.

“A standard litre of 4.2% fat and 3.4% protein requires 5.5MJ of energy,” he adds. Doing the maths, this means a cow only has to walk 2-3km (1.24-1.86 miles) a day to lose 1 litre of milk.

Focus on feed quality

While he agrees MFF is still relevant to rotational grazing, Sean thinks the focus should be on feed quality.

Chasing MFF as a metric could lead to poor decision-making, such as pushing production at the end of lactation, resulting in cows in light body condition at drying off.

If they are still in the same condition at calving, this will impact next lactation’s yield.

“Turning out too early, or staying out too late, also has an impact, so we need to think of longer term performance,” he adds.

Similarly, stocking rate has a big effect on MFF.

“Adding 1 cow/ha will increase output by 20% but reduce individual cow production by 8%.

“More silage or concentrates will be needed to increase that stocking rate – as you only grow a set amount of grass – and this is what reduces milk produced from forage.”

Yet Sean says it is difficult to calculate the true amount of milk production from grazing alone.

Some grassland managers, who use their feed budgets to do this, will be assuming that a cow eats 18kg dry matter (DM)/day consistently, from calving to drying off.

No cow achieves this, he says, which then undermines the accuracy of such figures.

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Measure milk from grass grown

A better KPI, he suggests, is milk from grass grown, worked out as a percentage. This means measuring the platform weekly.

The more concentrate fed, the lower the percentage. Farms can benchmark themselves year-on-year.

For spring-calving herds, Sean says the target is 80% (less in autumn herds as they house in early lactation and feed more concentrates overall) and includes grass grown on the milking platform and made into silage.

Silage made off the platform is not counted but instead makes up the remaining 20%.

Manage for good grass utilisation

Increasing production from grazed grass relies on good utilisation.

This is influenced by grazing conditions (for example, wet and cold weather or drought), infrastructure, and how well entry covers and residuals are monitored.

“A bit of grass analysis might be needed as, if you lose grass quality, you lose utilisation and might need supplements to balance it out,” Sean explains. 

“High utilisation in the first couple of rounds is important to avoid grass quality issues in summer, which, in turn, keeps up utilisation through the season.”

“The upper limit on entry covers must be no more than 3,200kg DM/ha, because grass becomes more fibrous, which means cows have to chew it, and digestibility drops as well.

“For best grass quality and the highest cow intakes, go in at 2,800kg DM/ha.”

Test the water to build confidence

Top grassland performers can reduce concentrate levels and see milk output remain static or even rise as cows consume more grass.

To build confidence in doing this, Sean’s advice is to cut out 1kg a cow/week in concentrates and see how it goes.

“It’s incremental and most farmers don’t notice any difference in yield,” he says.

But he admits lowering cake levels takes nerve, not least because in the first seven days, litres inevitably drop.

He finds most people bale out before the end of the week, not realising milk bounces back up to previous levels.

“If you take concentrates out and it doesn’t work, because there is something not quite right with the grass feed quality, you can always put it back in without any long-term detriment,” he points out.

“But give it at least a week.”

Put grass before concentrates

Another feature of success is to focus on grass first and see concentrates as an addition to – not part of – the feeding system.

“If cows are not hitting residuals, and grass is in the paddock, top farmers know they need to reduce their concentrate input, whereas average farmers adjust their grazing management to suit their concentrate rate.”

Sean advises about six grass tests spread through the year, with the first in February and the final one in October/November.

Regular sampling will confirm that rotationally grazed grass is comparable with concentrates at 12MJ of ME/kg DM and identify when nutritional quality needs topping up.

“For instance, in last year’s wet spring, proteins were shockingly low and needed balancing with a higher protein concentrate, and for the rest of the year they weren’t at their normal healthy state,” he says.

It is essential, however, to watch out for substitution, as this affects performance from grazed grass. A cow grazing 16kg DM/day and given 1kg concentrate does not automatically have a daily intake of 17kg DM, says Sean.

“It will be in the range of 16kg to 17kg because of substitution; similarly, when you replace grass with silage, it is never a one for one.”

Monitor profit

For those who are keen to improve their production from grazed grass, another KPI to follow is to monitor profit for every kilogram of grass grown.

Sean says this reflects how efficient the herd is at converting DM into profit and works out how well grass has been managed and used on the farm, removing variations such as land class or calving pattern.