The way in which animals graze can make or break a pasture. Cattle producers have traditionally put the needs of their stock first. However, in hard times when the requirements of animals and plants may be in conflict, the plants’ requirements must not be forgotten. Perennial grasses must not be sacrificed because of short-term desperation.
In drought conditions, it may be necessary to start hand feeding or to destock sooner than is considered necessary to maintain the stock, in order to ensure pasture survival, and speed recovery when useful rain falls. (For further information on managing pasture in drought, visit DroughtHub section of the website.)
Figure 1. Although these cattle are still in good condition, they should have been moved out of this paddock sooner to ensure survival of the pasture. This paddock may now need to be re-sown, and this may be more expensive than it would have been to feed the cattle.
The growth of pasture may be divided into three phases:
- Phase I: Pasture is very short (<3>
- Phase II: there is enough leaf for plants to grow rapidly.
- Phase III: growth slows down and quality falls as the plants mature and set seed.
The shorter the pasture, the longer it will stay in phase I when conditions improve. It is false economy to delay the start of hand feeding at the beginning of a drought, as this just means that your ‘green drought’ phase will last longer when useful rain finally falls.
In a normal season, keeping the pasture in its active growth phase (phase II) will maximise both pasture and animal production. At some stage, however, the pasture must be rested to allow it to mature and set seed, even though its quality will fall as a result.
There may be other reasons why grazing pressure is increased or decreased at specific times — for example, heavy grazing when an undesirable species is setting seed, in order to control its spread.
Continuous stocking of pastures can rarely be recommended. Some form of controlled grazing that includes periods of spelling that are timed to coincide with specific needs of the pasture is critical to productive, stable systems.
Effective nutritional management of the herd relies on the establishment of productive stable pastures that preferably contain at least 30% of a well-adapted legume. Where possible, and depending on the enterprise and market targets, properties should have a mix of pasture types (both native and introduced) to increase the options for grazing management.
In poor seasons, native pasture (being better adapted to Australia’s unreliable rainfall and poor soils) may produce more useful feed than will introduced species, which give greater production in good seasons.
Using grazing management to maintain or improve pasture quality has a distinct advantage over other management methods — it can cost almost nothing. If grazing management is not practised or is inadequate, more expensive inputs such as fertiliser and herbicides, and more frequent resowing of pasture, are likely to be required.
Effects of stocking rate on pasture
There is no static optimum stocking rate, as carrying capacity of a property varies from season to season and from one year to the next. Ideally, property stocking rates should reflect variation in carrying capacity through the timing of operations such as calving and sales, and in enterprise flexibility. Management’s values and attitude to risk will of course influence the approach.
There are usually higher returns per cow when stocking rates are low, but there are higher returns per hectare with higher stocking rates. At excessive stocking rates, the system may crash.
If a genetic improvement program or change of breed increases the weight of breeders in the herd, the need to alter stocking density or rotation length must be recognised. For example, 100 Charolais cross cows may eat 20% more than 100 British bred cows, and so will run out of feed sooner if no adjustments are made.
Figure 2. Lower stocking rates on rangelands may maximise animal production in the short term. However, in the long term, because animals have more opportunity to select the higher-quality pasture component, lower stocking rates may lead to dominance by ungrazed species of lower digestibility.
Stocking rate as applied at the paddock level, often called stocking density, is a very powerful pasture management tool. It can be used to actively control the quality and quantity of feed on offer and the survival of desirable or undesirable plant species. For example, high-density grazing with dry stock might be used to remove bulky dead pasture in order to prevent shading of new pasture growth. (Protein supplements for the cattle may be needed to encourage more complete use of low quality dry forage, but close monitoring is necessary to prevent overgrazing. See the section ‘Maintaining ground cover’.)
Both low and high stocking rates have the potential to substantially alter pasture composition. Different plant species will respond differently to grazing pressure. Annual grasses tend to be more competitive, and they germinate and grow faster than do perennial species. Thus if high stocking rates are maintained for too long a period, overgrazing may allow annuals to dominate and displace perennials, resulting in a shortage of forage outside the annuals’ growing season.
It also needs to be recognised that if the overall quality of the pasture is not high, animal production will suffer if stocking rate is increased to the point where selection of the higher quality pasture components is no longer possible. On the other hand, at low stocking densities, the opportunity to select the higher quality component of the pasture may maximise animal production, but the effect over time may be to allow the less desirable ungrazed plants to dominate. If stocking rate is not adjusted, the more desirable species may be lost, and the quality of the pasture overall will fall.
Successful/sustainable grazing management requires skill and experience. The key is flexibility — the rest period or rotation length needs to be adjusted depending on pasture growth rate and seasonal conditions.