Keeping your livestock well fed, healthy and productive year round, through good seasons and bad, is a challenge for all livestock producers.
Current drought conditions across much of eastern Australia are making this even more difficult with many farmers forced to supplementary feed.
However, in most seasons pasture feeding is the basis for livestock production and matching livestock requirement to the available pasture is the key to maximising production.
When planning livestock production from pasture the most important thing is to think energy and think dry matter.
There are two aspects of energy:
- energy requirements of livestock; and
- energy pasture can provide to livestock.
If we match the energy requirements of livestock to the energy provided by pasture, generally other things will look after themselves.
Pasture that is high in energy is usually high in crude protein and other nutrients.
Energy is expressed as megajoules of metabolisable energy (MJ ME).
Dry matter refers to the amount of pasture less its water content.
A lush growing pasture may be 80 per cent water and 20 per cent dry matter.
A dry pasture may be 10% water and 90% dry matter.
Using dry matter as a measure allows comparisons over a range of pasture quality and quantity for:
- pasture quantity – kilograms of dry matter per hectare (kg DM/ha);
- feed intake – kilograms of dry matter per head per day (kg DM/hd/day);
- energy from feed intake - megajoules of metabolisable energy per kilogram of dry matter intake (MJ ME/kg DM).
The energy requirements of livestock are met from feed intake and using fat reserves if there is a deficit from feed intake.
If livestock use their fat reserves to meet their energy requirements, they will lose weight and condition.
The energy that pasture can provide to livestock is determined by pasture quality and pasture quantity.
Pasture declines in quality as it matures because the digestibility of the pasture declines.
Digestibility refers to the amount of pasture intake livestock convert to meet their nutritional need.
A fresh growing pasture with good legume content may have a digestibility of 80% - the livestock can convert 80% of the pasture intake to meet nutritional need and only 20% is excreted.
Old dry pasture residues may have a digestibility as low as 40% - that is the animal can only convert 40% of pasture intake to meet its nutritional need and 60% is excreted.
As digestibility of pasture declines two things happen – the energy content of pasture declines and the consumed pasture takes longer to pass through the animal’s rumen so feed intake declines because of gut fill.
Pasture quantity also affects livestock intake.
Cattle need higher pasture quantity than sheep.
As a rule of thumb, feed intake for cattle is not limiting above 2600kg DM/ha and feed intake for sheep is not limiting above 1500kg DM/ha.
An estimate of pasture quantity can be made by measuring its height.
Putting it all together
The energy requirements of a 300kg steer are:
- 35 MJ ME/day to maintain liveweight (maintenance);
- 56 MJ ME/day to grow at .5kg per day (moderate production); and
- 74 MJ ME/day to grow at 1kg/day (high production).
As pasture quality (% digestibility) declines, the feed intake of the steer declines across all pasture quantities.
As pasture quality (% digestibility) declines, the energy per kilogram of feed intake declines across all pasture quantities.
As pasture quantity becomes limiting, the feed intake of the steer declines across all pasture qualities.
These concepts are addressed in the PROGRAZE course developed by NSW DPI and MLA, which have been delivered through Local Land Services NSW and Tocal College.
