How do sheep farmers maximise their output per acre? This is the nub of the question that Teagasc researcher Philip Creighton has been investigating for the last three years at the demonstration farm in Athenry.
His results are quite startling. They show that higher prolificacy sheep are key to getting more profit from your farming system. Even though the carcase weights tend to be lighter, Dr Creighton's research shows that the extra numbers more than compensate for any drop in carcase weight.
"Because higher prolificacy sheep tend to have lighter mature weights, they have a lower demand per head. Effectively, there is a greater proportion of the grass going into lambs than the ewe in the high prolificacy system," he said.
The farm at Athenry has been divided into six separate 'farmlets'. Despite the fact that no farmlet is more than 6ha, each is managed separately, and costs apportioned to generate profit monitors for all six.
The idea is to compare three different stocking rates - 10, 12 and 14 ewes per hectare - across two types of ewe prolificacy - 1.5 lambs per ewe and 1.8 lambs per ewe.
The high stocking rate/high prolificacy group produced the most lamb carcase weight per hectare, with 24 lambs, or 468kg, sold per hectare. This was over 150kg or eight lambs per hectare more than the low prolificacy group at lowest stocking rate.
But the group with the biggest gross margin was the high prolificacy group operating at the medium level stocking rate of 12 ewes per hectare.
The reason for this was simple - at the more extreme levels of output, the system became more reliant on bought in meal to supplement inadequate levels of grass. This, in turn, ate into the profitability of the system.
"At the end of the day, the amount of grass that your farm is able to produce determines the type of system that you can operate," said Dr Creighton.
"We are able to grow about 12.5t/ha of grass drymatter (DM). Yes, we did grow up to 1t/ha extra on the most heavily stocked areas, and we were able to get almost 10pc better utilisation of that grass at those levels, but the additional meal required hit the bottom line.
"The lambs at the low stocking rate were finished on a diet that was 97pc grazed grass. This dropped to 93pc for the medium stock, and even further to 81pc for the lambs stocked at 14 ewes per hectare," he said.
In addition, a bigger percentage of the lambs in the highest stocking rate system needed to be housed for finishing.
The next phase of the project is likely to focus on improving the average carcase weight for lambs at the medium stocking rates.
"We were operating at an average carcase rate of 19.5kg because it allowed us to keep lambs moving out of the system, but the aim over the next year or two will be to see how we can get closer to 21kg carcase weights at the same stocking rates.