Look after your grass so it can look after your sheep

Jack Munro of SAC Consulting believes that measuring and monitoring grass growth during the sheep grazing season is a key driver of business profitability. He offers some tips on how to get started.

Grass productivity can be measured in terms of hay and silage weight yields, but it is more difficult to pinpoint figures for grazed grass, says Mr Munro.

He says: “Appearances can be deceptive. A field may look green and contain the species we want to see. However, unless its yield is determined, there is a risk that livestock may be under-performing, and it may also increase the requirement for purchased feeds.

MORE NEWS | Find out if sunflowers and maize can feed your dairy herd

MORE NEWS | Suppliers of failed Mona Dairy likely to lose unpaid bills

“The utilisation of grazing data offers an opportunity for predicting potential forage excesses and deficits, allowing the producer to adjust the stocking rate. The old adage that ‘the difference between a good farmer and a bad farmer is two weeks,’ still rings true. Plotting and reviewing pasture data will give the producer added confidence for making stocking decisions.”

Building a pasture history allows for benchmarking over a period of years, and the ability to compare the farm with other businesses. One method for comparing grass productivity is to use Grass Check GB, an online grass monitoring project, which publishes grass growth and quality figures submitted by dairy, beef and sheep farms around the country.

Launched in 2019, the project is a collaboration between several industry organisations. Mr Munro also recommends joining a regional grazing group.

The cheapest option for measuring grass growth is to use a sward stick, although a plethora of other devices is available, he says. These range from handheld electronic plate meters to quad-trailed devices.

He cited the standard measurement targets for turning out ewes or lambs into a field and for moving them on.

“Using the recommended guidelines can greatly improve lamb growth rates and help to maintain ewe condition. Grazing priority should be given to weaned lambs and as a rough guide for the summer months, they will require at least 2,000kg/DM/ha of grass, measuring about 6-8cms in length, on a rotational system," he says.

“The covers should not exceed 2,770kgs/DM/ha, which equates to a grass length of an estimated 8-10cms. If it is permitted to grow taller, there will be too much unpalatable stem and dead material, which has significantly fewer nutritional benefits. This will risk failure to reach the target growth rate, which should be a minimum average of 250gms a day.

“The group should be moved on when the grass has been grazed down to 1,710kgs/DM/ha and measures about 4-5cms in length. Grazing past this threshold will not only impact lamb growth rates, but it will reduce sward recovery time. For a set stocking system, fields should be grazed at 1,710-2,240kg/DM/ha, which is roughly 4-6cms.”

Dry ewes in good condition will have a lower pasture requirement, he added. He suggested a minimum body condition score of three for a lowland type and 2.5 for a hill ewe.

“They could be turned into a field containing 2,240kgs/DM/ha, at which point the grass will be about 6cms long. They should be removed at 1,710kgs/DM/ha, at a grass length of 4cms. However, a lot will depend on other factors, such as planned tupping dates and whether a silage cut has previously been taken, for example.”

Overgrazing has a highly negative effect, he said.

“When grass is grazed down to below 3cms, or before the second leaf stage on a tiller, it can impact the timing of the tiller regrowth’s by up to 85 per cent. If the pasture is continually overgrazed, individual plants will be repeatedly forced to use their root energy reserves, without sufficient recovery time. This will compromise the overall health and vigour of the sward. Over time, it can lead to a reduction in the size and depth of the root system, making the sward less resilient to stressors like drought. At this time of year, it will also mean losing valuable nutrition for the flock.”

The goal for summer management is to give each paddock roughly 25-30 days’ rest, before being grazed again.

“Nevertheless, growing conditions will dictate the optimum rest period. Nitrogen fertiliser applied to the grazing platform in the first half of August can give better value for money compared with creep feeding, as long as an effective response is achieved in well-managed paddocks. Measuring grass is the only accurate way to assess the response to summer-applied nitrogen fertiliser. Swards with a red and white clover content higher than 30 per cent may not see a benefit from nitrogen, so species composition is also a relevant issue.

“Failure to avoid over or under grazing grass will result in a decline in dry matter and nutritional quality, which in turn impacts business profitability. Grazed grass remains the cheapest feed for sheep, but it requires regular attention to produce optimal flock performance,” says Mr Munro.