Matching the grazing system with livestock requirements
Both the quantity (kg DM/ha) and quality (MJ ME/kg DM) of feed on offer (FOO) are important determinants of animal growth and the major feed-related controls. However, pasture quality is much more important than quantity.
Match expected pasture quality and growth rates to livestock demand (number and type of animals) to achieve nutritional objectives.
For livestock of the same age, weight, genetics, sex and physiological state to achieve maximum animal productivity from pasture, four principles apply:
- As quantity of available pasture (kg DM/ha) increases, feed intake will increase until a plateau (maximum intake) is reached. Maximum feed intake is achieved somewhere between 2000kg DM/ha (sheep) and 3000kg DM/ha (cattle) of available pasture.
- At the same level of feed intake, as feed quality increases - and to a lesser extent protein content, so does the rate of liveweight gain.
- As feed quality increases, livestock eat more and energy intake increases, liveweight gain increases, but the total amount of feed eaten to achieve the liveweight gain decreases.
- At the same amount of feed on offer, feed intake will increase when feed quality increases.
Apply these fundamental principles to grazing management decisions to achieve livestock production targets.
The upper limit of growth of an individual animal at any point in time is set by its genetic make-up, disease status, birth type (twin or single) and rearing type of the animal. However most of the variation in animal growth is due to the variation in the quantity and quality of available pasture.
Higher quality pastures provide more options to achieve market specifications. As plants mature, the ratio of green leaf to structural (stem) material increases, leading to a marked decline in feed quality. Digestion rate within the animal slows with declining feed quality.
As gut-fill increases, it starts to depress appetite and feed intake. This will eventually result in animals losing weight while grazing low quality pastures, even if pasture availability is not limited.
Sheep and cattle manage the decline in pasture quality by grazing selectively (sheep more so than cattle), giving them a diet higher in energy and protein content than the average available. However, selective grazing can reduce pasture production and persistence over time.
Rotational grazing can help reduce the impacts of selective (or patch) grazing.
Cattle tend to graze less selectively than sheep and do not display strong camping behaviour. Under set stocked conditions, this often means a paddock will be more evenly grazed by cattle.
Enterprise type and reproductive cycles
Matching lambing or calving times to seasonal pasture growth and growing season length is critical for optimal pasture utilisation.
Optimise stocking rates and reduce the need for supplementary feeding by matching lambing or calving times to the pasture growth cycle.
The timing of stock sales, purchases or agistment can be used to further refine the system.