The amount of pasture consumed by grazing animals in a day (feed intake kg/day) combined with the energy content (MJ/kg DM) determines the energy intake (MJ/day) of an animal. If a ewe eats 1.2 kg/day DM of a pasture with an energy content of 10.2 MJ/kg DM, then the ewe will have an intake of 12.2 MJ/day.

The ME intake (MJ/day)of animals is determined by the Feed On Offer (FOO) as this will dictate how long they spend grazing and if they can get their requirements, and the nutritive value of the pasture. Factors that influence the nutritive value of the pasture include;

Pasture species; Improved sown pastures are usually higher than native species
Stage of growth; Green and vegetative higher than reproductive or dry herbage
Legume and clover dominant pastures; At the same digestibility, an animal can eat more clover compared to grasses, consequently consuming more energy on a daily basis and exhibiting improved animal performance.
Vegetative freshly grown pastures higher than for older rank pasture.
Leaves rather than stems; stems are generally less digestible than leaves

The other important consideration influencing animal intake is the height of the pasture. It’s possible to have 1,100 kg/ha FOO evenly across the ground about 2 cm high. Alternatively, there could be 1,100 kg/ha in clumps 5 cm high with bare ground or dry pasture in-between (common with lucerne or chicory pastures). As shown below, animal intake is much higher on the taller rather than the shorter pasture.

Some examples of how ME intake is influenced by energy content of the pasture, FOO values and pasture height are shown below. All pasture and ME intake values are for a 50 kg animal (1 DSE), the pastures contains 15% legume in temperate regions with flat topography, in mid-winter.

Interaction of FOO, pasture height and digestibility on ME Intake

The Lifetime Ewe Management project provides charts to allow quick estimates of ME intake of dry, pregnant and lactating ewes grazing a wide range of pastures.