This article was written by Breann Saulnier, OMAFRA Grazing Livestock Assistant
You may look out into a pasture and see an abundance of tall, delicious-looking grass for livestock to graze but this is not necessarily what the livestock see. The amount of forage available for grazing is the portion of plant material that the animal chooses to eat, not the total amount of forage growing that is visible. So how do you know what the animal will choose to eat? Well, the palatability and the utilization forage for animals is influenced by what stage of growth the grass is in. In the context of grazing, palatability refers to a measure of when animals are given free choice, choose to graze one pasture over another. Utilization is the amount of forage that is consumed out of the total available forage.
Grazing livestock have a strong preference for green plant material. Green plant material refers to the new growth or regrowth of forages that are in the vegetative phase. The vegetative phase consists predominantly of leaves on the tillers and less stem material. Livestock look to eat the new green leaves of the plant before eating stems, as leaves are more palatable. From a nutritional perspective, new growth leaves also provide a large amount of energy, protein, and important nutrients that grazing animals require to meet their demands.
Mature forage is not as palatable to livestock and when present will reduce their consumption out on pasture. Not only is the mature grass unappetizing to livestock, it is also tough to digest and more difficult to bite off due to the tall height of the grass.
Performance and Grazing Management
The performance of grazing animals is affected by the quantity and quality of forages. The goal of managing pastures is to grow forages to an optimal nutritional value and have it consumed by livestock with little waste. However, pastures vary in the dry matter content, fibre, nutrients, and palatability. This variation could lead to lower milk production and animal gains compared to animals fed a concentrate ration. Producing a lot of forage will also not be beneficial if it cannot be properly utilized by the animal. The same can be said about too short of forage available. Animals will graze down to about 5 cm above the ground and forage shorter than this is difficult for them to bite off. Variability can be minimized by properly managed grazing systems and understanding the selectivity of the animals grazing.
Pastures that are grazed with low intensity, such as in a continuous system, will have low pasture production. Cattle are more spread out in continuous systems which causes both overgrazing and undergrazing throughout the pasture. Forages that are undergrazed will be too mature for consumption, while the forages overgrazed will have slower rates of regrowth. If the management intensity is increased like in a rotational or strip grazing system, there will be a significant increase in the pasture output per unit area. This is due to a higher stocking density with shorter grazing periods in multiple paddocks and a longer recovery period for grass regrowth. Utilization is improved and the forage is able to regrow to optimal heights and palatability for grazing.
Improving the grazing management can also improve your land efficiency by allowing you to graze more cattle or even devote the extra land to other uses such as for hay. The decision to go from one type of grazing system to another has to be based on the potential output of the new system and the overall cost of developing it including fencing, water, labour, and time to move the animals.
Animal Grazing Behaviour
Observing the behaviour of grazing animals can provide helpful insight into what the forages are like on pasture from the perspective of the animal. When there is limited green plant material in the pasture, livestock will spend more time selecting and searching for it, increasing time spent out grazing in order to get their nutrients. With a pasture containing high quality and quantity forage, livestock are seen to reduce their time spent grazing as they can eat less while still getting the nutrients they need to feel full. With cattle, their strong preference for new growth plant material will take over their impulse to eat quickly until full, potentially causing some loss in body condition when new growth is low. Cattle that appear restless can also indicate that the pasture available is poor. In addition, herd animals can be seen to graze together as a herd when there are large amounts of forage available, versus grazing more individually when forage is less available.
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