Grazing method is a critical factor in efficient pasture and animal management. For perennial pastures the choice of grazing method is particularly important to ensure plant persistence while maximising pasture utilisation and livestock performance.
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.
There is considerable interest among livestock producers in using different grazing methods to improve productivity, maintain desirable pasture species and reduce land degradation.
Historically set-stocking was the only grazing method used with annual pastures. Under this system, stock were moved from paddock to paddock on an ad hoc basis, remaining in each paddock for varying periods and in some cases months. In contrast, rotational grazing involves the frequent movement of large groups of stock through a series of paddocks.
The difference between the methods is that set stocking largely enables the animal to control where, when and which plants it eats where as the higher grazing pressure of rotational grazing, means the 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. This section briefly discusses how different grazing methods impact upon the productivity and persistence of perennial pastures, livestock production and land degradation.
Different grazing methods:
Grazing method is a procedure or technique of grazing management used to achieve a specific objective. Set-stocking and rotational grazing are examples of grazing methods, but there are many more. Farmers can become confused when confronted with the large range of grazing methods, e.g. set-stocking, rotational grazing, strip grazing and cell grazing, etc. 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. However, very few producers use this grazing method in its strictest sense but rather leave stock in the same paddock for long periods, especially during the growing season. Intensive rotational grazing involves moving stock daily and in some cases more than once per day with pastures receiving a long rest between grazings.
With rotational grazing stock are either moved on the basis of time (e.g. four paddock lucerne system with two weeks grazing followed by six weeks rest), or variable recovery time under the ‘Savoury’ approach, plant growth stage (e.g. three-leaf stage), animal intake (e.g. maintain maximum intake) or feed-on-offer (FOO). 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
- stocking pressure during grazing increases
- rest period for each paddock increases
- animals’ ability to graze selectively is reduced
- average stocking rate (i.e. grazing days/ha) stays the same.
Some farmers use an intensive rotational grazing method developed by ‘Savoury’, the principles of which are to:
- control rest to suit the growth rate of the plant
- adjust stocking rate to match carrying capacity
- use short grazing periods to increase anima performance
- use maximum stock density for the minimum time
- use a diversity of plants and animals to improve ecological health
- 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 different grazing methods tactically on the basis of seasonal conditions and livestock and pasture requirements. For example, in situations of feed deficit rotational grazing allows better control over the regrowth period than set-stocking and can be used to restrict livestock intake. Conversely, in a situation of feed surplus set-stocking at high stocking rates can be used to control FOO and allow animals to select a high quality diet.
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 leaf area the higher the potential growth (FOO provides an estimate of leaf area).
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 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 monitoring pasture growth and using indicators to maintain the optimum FOO for pasture growth for the longest possible time, e.g. grazing at the three-leaf stage.
When FOO is plotted against pasture growth rate for kikuyu (Figure 1), it becomes apparent that the fastest growth rate increases occur up to a FOO of about 1400 kg DM/ha, after which pasture growth rates continue to increase but more slowly. Grazing systems that enable a kikuyu pasture to be maintained >1400 kg DM/ha have the potential to increase production.
An application of this principle is to defer kikuyu pastures at the break of season until they reach ~1400 kg DM/ha then graze and maintain at 1400 kg DM/ha throughout autumn and winter. In spring allow FOO to fluctuate between 2000 and 3000 kg DM/ha to optimise pasture growth and liveweight gain in stock. Another example is rotational grazing systems that maintain the majority of paddocks, cells or strips at ~1400 kg DM/ha or higher.
For other perennial pastures with a more upright growth habit than kikuyu (e.g. lucerne), the minimum levels of FOO are likely to be lower.
Information Sourced From:
