BEST GROW GRASS AND CLOVER ALONE
Trying to grow white clover
with grass in a mixed
sward may not be the best
way to maximise potential
of the crop or animals.
Jessica Buss reports
GRAZING animals prefer to eat more clover than grass when offered separate swards of both, side by side, and sheep achieve higher feed intakes than on mixed swards which should improve yields or liveweight gain.
Thats according to Mark Rutter, Institute of Grassland and Environmental Research, North Wyke, Okehampton, Devon, following studies which allowed sheep and cattle to choose the forage they preferred.
He believes that practical systems which promote the expected performance benefits of grazing separate grass and clover plots on farm could be developed within five years.
In IGER studies white clover was grown alone in monoculture plots next to grass only plots – giving adjacent monocultures – for studies on grazing behaviour. When offered a choice, both cattle and sheep selected clover for about 70% of their forage intake and grass for the other 30%.
"Both showed a preference for clover even when only a quarter of the ground area offered is clover. But the intake of clover is influenced by how much is available." However, they didnt eat much more than 70% clover a day even when more clover was offered, says Dr Rutter.
When sheep grazed these adjacent monocultures they achieved higher daily dry matter intakes than on a mixed grass/clover sward. According to Dr Rutter, this indicates that grazing adjacent monocultures offers potential to increase dairy cow milk yields and lamb growth rates.
In an early part of one study when grass and clover quality was ideal, milking cows ate 23kg DM a day of 70% clover and 30% grass, much more than normally eaten from a mixed sward.
"However, preference for each forage changes as the day progresses. The animals eat more clover in the morning and a higher proportion of grass as the day goes on." In the study clover intakes were 90% in the morning, falling to 50% by evening.
"It may be that animals are trying to avoid grazing at night, by filling up with a bulky feed with a slow rate of passage through the digestive system. But in the morning they want something with a quick return on nutrients such as clover; the same as we eat muesli for breakfast and pasta for supper."
Animals appear to want to avoid grazing at night, preferring to ruminate. This is possibly in an attempt to avoid attacks by imaginary predators, but which historically these animals would have feared, he adds.
Higher feed intakes, achieved on adjacent monocultures, may occur because the animal can select what it wants at a particular time of day more easily than on a mixed sward. When its easier to make a choice, they can eat more in total.
Sheep and milking cows also eat more clover in a given time than grass. In one comparison, cows ate 28g DM/minute of grass and 41g DM/minute of clover, explains Dr Rutter.
"We are currently investigating how they achieve this," he added.
"However, sheeps ability to eat clover more quickly than grass may relate to their biting and chewing behaviour. Usually, half their jaw movements are chews and half bites. But when eating clover they dont need to chew as much, because it has less structural fibre, so can bite more."
Cows, however, only chew for about 20% of their jaw movements so havent the option to bite instead of chew in the same way, says Dr Rutter.
But even though cows and sheep can eat clover more quickly than grass, they choose to eat some grass even in the morning.
"That possibly relates to animals digestive function. They need some roughage to maintain proper rumen function. If they ate just clover their rumen flora would change and they wouldnt be able to digest grass as efficiently when clover was in short supply."
One advantage of growing grass and clover separately is that there is no competition between the two crops, resulting in less variable clover availability.
It also makes it possible to treat the crops differently when applying fertiliser or herbicide. Dr Rutter believes that growing the crops in strips may still allow grass to benefit from nitrogen fixed by the clover as in a mixed sward.
Studies also discovered that when clover was in short supply due to over-grazing, animals increased their intakes of grass, allowing clover to recover. The clover also adjusted by growing more, smaller leaves.
Further studies this year will focus on potential milk yield increases from offering adjacent monocultures. Other studies on animal growth rates, supplementing animals effectively and managing clover and grass in separate blocks will also be required before adjacent monocultures can be put into commercial practice.
A system for managing cattle and sheep on adjacent monocultures could be ready to use on farm within five years. This has potential to help improve farm profits through increased animal performance, but adequate research funding is yet to be found, adds Dr Rutter. *
• Higher feed intakes.
• Improved production.
• Easier sward management.