How to maximise animal, pasture production
Historically, set-stocking was the only grazing method used with annual pastures. Under this system, livestock were moved from paddock to paddock on an ad hoc basis, remaining in each paddock for varying periods, in some cases for months.
Grazing method is a procedure or technique of grazing management used to achieve a specific objective. Farmers can often become confused when confronted with the large range of grazing methods, for example, set-stocking, rotational grazing, strip grazing and cell grazing. However, all these grazing methods fall on a continuum between the two extremes of (strict) set-stocking and intensive rotational grazing.
Under (strict) set-stocking, animals remain in one paddock for the whole year and the pasture receives no rest. Few producers use this grazing method in its strictest sense, but most do leave stock in the same paddock for long periods, especially during the growing season.
In contrast, rotational grazing involves the frequent movement of large groups of stock through a series of paddocks.
Set-stocking enables animals to control where, when and which plants they eat, whereas the higher grazing pressure of rotational grazing means animals have less ability to choose. Rotational grazing allows the producer to decide when and for how long a pasture will be grazed and rested.
_Pasture species effect on grazing method _
With most perennial species, some form of rotational grazing is essential to ensure persistence in the medium to long-term. A number of studies have demonstrated that the density of perennial pastures declines rapidly under set-stocking. Kikuyu is an obvious exception as it persists under set-stocking and can respond to high grazing pressure. There are a number of species including tagasaste and some of the temperate perennial grasses that persist under set-stocking with cattle but not with sheep.
In the case of annuals it is important to understand how grazing management will influence seedling establishment and seed set. Deferring grazing following the break of season will allow annual seedlings time to establish and in spring aerial seeding annuals time to set seed. In the case of subterranean clover hard grazing in spring stimulates greater seed set.
_When to move stock _
Food On Offer (FOO) is the amount of pasture in front of an animal at any one time, measured in kilograms of dry matter per hectare (kg DM/ha). This refers to the total amount of pasture present if cut at ground level, and including both green and dead material.
FOO is a balance between pasture growth and the removal of pasture by grazing animals. It is a useful indicator for managing both animal and pasture production.
With rotational grazing, stock are moved either on the basis of time, variable recovery time, plant growth stage, FOO or animal intake _(see box, above right) _.
Grazing method is a critical factor in efficient pasture and animal management, particularly when maximising pasture utilisation and livestock performance.
Another key factor in rotational grazing is the number of paddocks in a rotation. As the number of paddocks increases the grazing period for each paddock decreases, the stocking pressure during grazing increases and the rest period for each paddock increases. The animals' ability to graze selectively is also reduced and the average stocking rate (that is, grazing days per hectare) stays the same.
_Intense rotational grazing _
Some farmers use an intensive rotational grazing system, the principles of which are to control the rest stage to suit the growth rate of the plant, adjust stocking rate to match carrying capacity and plan, monitor and manage the grazing. It also allows farmers to use short grazing periods to increase animal performance, use maximum stock density for the minimum time, use a diversity of plants and animals to improve ecological health and use large mob size to encourage herding.
In reality, no single grazing method can meet every animal and pasture objective. The best approach is to use a grazing method that suits your livestock and pasture goal. Given that your goals will change throughout the year so will the grazing method employed. For example, set stocking is best for achieving the highest growth per head while rotational grazing the best growth per hectare.
_Pasture production _
Optimising pasture production depends on controlling two variables - the residual FOO following grazing and the length of time pastures are allowed for regrowth. In general, the higher the FOO the higher the potential growth.
If residual FOO is too low, pasture growth will initially be slow due to the low leaf area available for photosynthesis. If the period of regrowth is too short, then pastures will only experience high growth rates for short periods or not at all.
Conversely, feed quality declines as plants mature, so there can also be a trade-off between biomass production and quality. All grazing methods with the objective of maximising production involve ongoing monitoring of pasture growth and using indicators to maintain the optimum FOO for pasture growth for the longest possible time, for example, grazing at the three-leaf stage.
_Animal production _
It is commonly thought that rotational grazing results in more pasture dry matter production and as a consequence allows higher stocking rates. In recent comparisons between set-stocking and rotational grazing in which production was optimised, the stocking rate was 5-15 per cent higher with rotational grazing.
The liveweight gain per head was lower under rotational grazing in the prime lamb studies, but there was little or no difference in wool cut per head in trials involving Merino wethers. In general, when pasture availability is non-limiting, livestock production per head will be higher with set-stocking as it allows animals to select a high-quality diet.
However, this may lead to the loss of the most palatable or highest quality species in the pastures so that in the medium to long-term animal production will decline. The combination of high stocking rates and set-stocking can lead to an increase in the subterranean clover content, which can also improve performance per head.
In contrast, rotational grazing usually leads to an increase in the grass component, which increases production per hectare.
Large paddocks often contain areas of pasture that are ungrazed or grazed infrequently. If large paddocks are subdivided and rotationally grazed, pasture that was previously under-utilised will be consumed - leading to an increase in production. A similar result can be obtained by grazing large paddocks with big mobs, thus reducing selective grazing by livestock.
Rotational grazing can be used as a tool to assist in the control of internal parasites, either by using cattle to clean up a pasture for sheep or ensuring that livestock are not exposed to heavy worm larvae pick-up. This requires planning and an understanding of larval survival patterns. In set-stocked situations clean paddocks can be prepared.
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