Kerry Dwyer

Driving around the South Island over spring I have seen that many farms have not succeeded in the great lamb growth challenge. Lambs can grow at 400-500g/day pre-weaning, yet so many farms do not achieve those levels.

Lambs growing at 400g/day will wean at 40kg at 90 days, but many farms struggle to reach 35kg weaning weights. Sheep genetics available today can deliver higher production in terms of ewe milking and lamb growth abilities, while farmers can sort out factors such as ewe condition, mineral levels and worm control. Which left me thinking about management of pasture quantity and quality while I drove.

In theory we lamb in spring so peak milk production coincides with peak pasture growth. But too many farmers set stock too early, with pasture cover too low to allow this to happen. We know green grass grows green grass, so if pasture growth rates are higher pasture covers are higher. To the extent a pasture at 1500kg drymatter (DM)/ha can grow 10-15% more a day than one at 1200kg DM/ha. Set stocking at low pasture covers therefore limits pasture growth, pushing peak pasture growth later in spring. One week’s spring growth can add pasture cover that grows a bigger benefit over spring.

Clover production is strongly influenced by previous summer and autumn management, meaning the stronger it is going into winter the stronger it is coming into spring.

Of course, set stocking on to high pasture covers can result in some bearing issues, but what you may win in the bearing roulette (with low pasture covers) you can lose double or treble in the lamb growth challenge. Lamb growth rate drives income and profit, because the faster-growing animals eat less feed giving a greater return per kg DM and more feed for other stock. Lamb growth rate drives lambing percentage.

Many farms set stock and lamb too early. Being optimists, farmers will target the one-in-10-year pasture growth rather than the average or the lesser end of the scale. Do the maths – 120 days at 300g/day equals 90 days at 400g/day.

Farmers can also manipulate pasture cover at lambing by applying some nitrogen in autumn or late winter. At $8/kg carcaseweight it is due serious consideration.

Part of the spring pasture cover equation is the ability of ewes to eat it. Gut size conditioning is quite important. If you have underfed stock for a period they take time to adapt to higher intakes. A ewe feeding twins growing at 400g/day has to peak at eating more than 25kg wet pasture a day, maybe over a third of her liveweight about three weeks after lambing! If her gut is not conditioned and if pasture cover is low and it takes too long for her to harvest it won’t happen.

So, if the ewe is to eat 25kg wet pasture/day it also must be top quality. And if the lamb is to eat the maximum as it grows, that also has to be top quality. Sheep and cattle prefer a diet of 70% legume and 30% grasses, but most pastures are lucky to supply the opposite. Lambs can achieve 400g/day pre-weaning on lucerne, which sets a target for other pastures. If we can get more clover into a mixed pasture then lamb growth will benefit.

Clover production is strongly influenced by previous summer and autumn management, meaning the stronger it is going into winter the stronger it is coming into spring.

Go back to when new pastures are sown – most that I see are sown in spring. Clover is slower to establish than grasses, and annual weeds love spring sowing. So, clover struggles with spring sowing. To compound that, farmers sow high rates of grass seed, to combat the weed issue, which smothers clovers more. The net result is less than 10% clovers in pasture. Autumn sowing and lower grass seed rates will give higher clover content in pastures, for many years. If we have good clover content in autumn, and give it the right management in spring, we can give our lambs a kick start.

How have your lambs fared in the great lamb growth challenge? After 40 years of farming sheep I have often heard farmers blame the season for poor results, I would rather have well-grown lambs. Lambs will seldom achieve growth rates post-weaning that are possible pre-weaning, so it is worth some serious thought. It is easy to be pushed into weaning because of something that didn’t click earlier in the season.

  • Kerry Dwyer is a North Otago farm consultant.