Joanna Grigg
It’s knowing when to hit it hard and when to keep off.
Building a pasture feeding system that supplies quality and bulk when you need it means grazing must be managed to pasture species.
There are compromises to be made and farmers need to weave together stock demands and plant demands.
A Massey University study (published NZ Grasslands Association, 2018) showed lamb growth rates in late summer/autumn on plantain and red or white clover were directly related to the amount of stem residual developed in the plantain from spring.
The study on three farms showed grazing management during spring that maintains control of plantain stems and encourages the presence of clover, is key to high lamb liveweight gains on plantain-clover mixes in late summer and autumn.
Results suggest rotational grazing in spring, to stop the plantain stems forming yet giving clovers a chance to recover between grazings, would be a good approach. Adding cattle in with lambs in autumn, helped clean up plantain stems.
The study monitored pre- and post-grazing herbage masses, botanical composition and quality of plantain-clover mixes across three commercial farms throughout late-summer and autumn.
One farm had a large amount of dead stem (>20% of dry matter) throughout February, March and April. Between February and April lambs grazing this pasture consistently lost weight. However, once the dead stem was removed and the sward was mainly live leaf (89% of DM), reasonable lamb growth rates (151g/day) were seen during May.
All three farms maintained pasture covers over seven centimetres (1200kg DM/hectare) over the trial, so the clovers were never grazed out hard. If plantain-clover swards are consistently hard-grazed, as seen with set-stocking, this can lead to a plantain-dominant sward.
Permanent annual clover and grass pasture requires a different approach to management than seen with plantain/perennial clovers.
In this mix, grass is the number one competitor. Hitting grass hard in July with high stocking rates (perhaps using strip grazing) will shorten down grass tillers and expose the annual clovers to light. If stock are then kept off the block for a few weeks, the clover content will increase rapidly.
Strip-grazing the pasture to remove grass competition provides a good feed source for ewes over winter pre-lambing. Annual clovers grow at lower soil temperatures so get ahead of white clover.
Results from the Beef + Lamb New Zealand-funded ‘MaxClover’ grazing experiment, carried out by Lincoln University, showed superior clover content in sub clover/cocksfoot pastures gave greater liveweight gain per hectare from August to October than white clover/ryegrass or white clover/cocksfoot pastures.
Every five to seven years grazing management should focus on increasing the legume seedbank. To do this, keep the block unstocked during autumn, while the next batch of annual clover seedlings establish. Graze over winter but then destock mid-October, as annual clover flowers and sets seed.
Lucerne is a forage that farmers can get on to with stock in spring, but needs a spell in autumn. The NZ Forage Systems Factsheet states spring grazing can start when plants are at 1500kg DM/ha.
Farmers do not need to wait until spring flowering to graze stands with ewes and lambs. That said, target the older stands coming up for replacement as the first blocks to be grazed, to give the newer blocks a few more days to grow.
Spring rotations with ewes and lambs should be five to seven days, with the residual cleaned up by cattle. Spelling should be 35 to 42 days. Professor Derrick Moot, Lincoln University, has calculated that a 30ha stand can take 300 ewes with twin lambs through a rotational grazing on six breaks of five ha each.
The time to keep off lucerne is autumn, where at least 50% of the stems should be allowed to flower. This encourages root growth and persistence.
