To have plants with well developed roots to provide energy from the plant for regrowth and to supply plant needs from the soil; and
- to maintain adequate leaf area allowing plants to trap sunlight.
- To maximise growth rate after grazing, have plants with a good root system and sufficient residual leaf area. Pasture plants then regrow immediately. Regraze before the oldest leaves die.
Do this in rotational grazing by adjusting grazing intensity and rotation speed. Do this in set stocked systems by adjusting stocking rate (and thus grazing intensity).
Sheep and cattle have different feed preferences and different grazing behaviour. But both sheep and cattle select leaf in preference to stem, and stem in preference to dead material.
When FOO is high, sheep will:
- select green material;
- tend to graze closer to the ground in preferred spots ( patch grazing);.
- select leaf material; and
- have a greater impact on the botanical composition of the pasture than cattle.
Cattle, on the other hand:
- also select green material;
- are less selective;
- cannot graze as closely as sheep; and
- have a longer period of need for higher quality feed than sheep.
Mature dry cattle can be used to ‘condition’ rank pastures by removing taller shading grass and encouraging clover growth. They are also less selective than sheep and will remove more dry feed when mixed with green, even though it is of lower quality. However, performance of productive animals (lactating cows, growing yearlings) will fall if the overall quality of the pasture is poor.
Mature dry cattle can also be forced to graze harder than the cow and calf herd without harming production. In a rotational grazing system the cow and calf herd is moved on when the FOO drops too low to maintain optimum production and a herd of dry cattle, such as heifers, may be used as followers.. Use the heifers after the cows to graze the pasture lower and prevent patch grazing occurring.
Selective grazing will occur according to variation in attractiveness of a plant to the animal. Livestock avoid undesirable plants such as maturing silver grass (Vulpia sp.), barley grass or dock, with consequent increased grazing pressure on the more preferred species.
This results in the undesirable species becoming more dominant and the preferred species being overgrazed. In perennial pastures the same effect occurs in the dry months when the annual component of the swards has dried out. Sheep, and to a lesser extent cattle, select the green matter of the perennial plants.
The resulting grazing pressure on perennial plants in summer can be very high and is proportional to the perennial plant density. Always remember that in our environment annual pastures are very forgiving of poor grazing management decisions. Old pastured areas often have a good seed bank, which ensures a pasture the following year.
However, to maintain temperate perennial grasses in the sward, it is vital to manage grazing to retain plant numbers. Generally the greatest number of perennial plants in the paddock occurs in the year of establishment.
With little or no seedling recruitment, the perennial component will only decrease in number over time, although it does increase in crown size. Exceptions to this are perennial ryegrass (more than 700 mm rainfall) and kikuyu grass, both of which regenerate from seedlings.
Rotational grazing favours the persistence and productivity of perennial species compared to set stocking. When assessing pasture, do not simply look at total FOO, but keep an eye on the different species. Look at the clovers and see if they are being grazed heavily when grasses are not. Check whether some grass species are being grazed more than others.
Animals continuously grazing a mixed pasture do not always select a particular species. Selection varies throughout the year depending on the nutritional status and palatability of the different components. In continuous grazing, grazing pressure and the pattern of the break of season are likely to have a greater effect on botanical composition than the grazing system itself.
The invasion of weeds and undesirable species is a response to grazing management or other factors such as soil fertility. If desirable species are threatened, modify the grazing management or other factors involved.
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