New Zealand sheep enterprises have evolved over the last three decades with a focus on eliminating costs and driving performance from grazing systems, be this ryegrass or clover swards, forage crops or alternative forages.
At part one of the Teagasc sheep conference on Tuesday night, professor of sheep husbandry and head of agriculture and environment at Massey University, New Zealand, Paul Kenyon said the golden rule for top animal and farm performance is to adhere to optimum grazing heights, irrespective of the crop in question.
The dominant herbage in place on New Zealand farms is a ryegrass or white clover sward type.
While the grazing strategy in place is a rotational grazing system, except for the final two weeks of pregnancy and during lactation, with a set stocked system of grazing used during this period.
Herbage cropping occurs on average on less than 7% of the farm.
This is viewed as delivering the best opportunity of providing enough feed across the year, with New Zealand sheep farms developed on the principle of not bringing any supplementary grain feed on to their holdings.
For ryegrass or white clover swards, the optimum grazing height is 4cm to 8cm or a cover of 1,200kg DM/ha to 1,800kg DM/ha, whereby the quantity of feed available is measured from ground level.
Paul outlined that this range in sward height will satisfy the basic principles of achieving high levels of animal performance from a herbage only system.
There are times when insufficient feed availability will not allow these grazing strategies to be satisfied and in such circumstances, Paul says it is vital to know what covers are present, predicted herbage growth and animal demand, so that you can prioritise which class of sheep can be fed within the optimal range and which sheep can be made to work harder and do with a lower level of feed.
In-lamb ewes were used to detail how this works in practice at farm level.
Paul explained that New Zealand farmers use whatever information is available to inform their decisions.
For a farm faced with insufficient feed and ewes are entering late pregnancy scanning results, ewe condition and lambing date will all be used to apportion feed.
For example, ewes lambing in the first and second cycle might be offered access to swards where they will graze down to 3cm or what is deemed slightly above maintenance levels.
Ewes carrying single lambs and lambing in the third cycle will graze down to 2cm and use body reserves to buffer demand until feed supplies improve.
This hierarchy system will remain in place until feed supplies have increased to a level that allows feed allowance to be increased.
This may mean transferring ewes to a set-stocking grazing system in advance of lambing, but maintaining what are classed as non-priority ewes (later-lambing ewes or single-bearing ewes) on a rotational grazing system with a less than desirable level of feed with the focus at all stages remaining on avoiding the introduction of supplementary concentrate feeding.
Central to operating such a system successfully is matching the farm’s lambing date to the normal commencement of grass growth and sufficient feed availability.
Quality and quantity
Ewes and lambs remain in a set stocking system from prior to lambing until weaning.
The stocking rate and group size will depend on the level of herbage available at the outset, along with taking predicted growth in that area into account.
The planned stocking rate is geared at maintaining sward height between 4cm and 8cm during this period.
Weaning typically occurs at 100 days after the first lamb is born, meaning the majority of lambs will be aged 80 to 100 days, while there could be lambs as young as 66 days of age in the group.
Post-weaning lambs become the priority group, but a hierarchy system remains in place for ewes, with those lacking condition grazing swards to 3cm, which is viewed as slightly above maintenance demands and capable of supporting some recovery in body condition, while ewes in adequate body condition are used to clean off paddocks to ensure grass quality is maximised for grazing lambs.
Feed availability dictates decisions on selling lambs as the year progresses and whether lambs will be carried through to slaughter or sold as stores.
Paul summarised major changes in the sheep sector, with productivity gains including increasing the number of lambs weaned from one lamb per ewe joined to 1.35 lambs and increasing the carcase weight from 15kg to 19kg as going a long way to compensating for the ewe flock falling from 45m head in 1990 to 28m head in 2020.
With these gains, albeit from a low base, sheep sector output has fallen by just 8%.
Sheep conference part two
Thursday’s conference (28 January) will examine how genetics and breeding can reduce labour at lambing through improving lamb vigour and ewe mothering ability.
The second is on Laryngeal chrondritis, a disease of the upper respiratory tract of sheep.
It runs from 8pm to 9pm. Register online at www.teagasc.ie/sheepcon21.