Growers planning to graze a barley, oat or wheat crop this season might now be contemplating when to let their sheep into the paddock, or even how to go about it. Following are a few factors to consider that might help with grazing management over the next few months.
When to start grazing
Grazing can commence once plants have ‘anchored’ (have nodal roots at the plant base). To test if crops are ready for stock, growers can use the twist test. Simply pinch the top leaves of the plant, twist and pull upwards. If the leaves break off and the plant does not pull out of the ground then the crop can be grazed.
Be careful in drier conditions. Nodal roots are initiated as tillering commences. The first tiller appears when the third leaf emerges. Thereafter, as each leaf and subsequent tiller appears, another nodal root starts to develop. If plants aren’t actively growing and putting out new leaves and tillers, these roots won’t be initiated.
Under dry conditions root elongation is inhibited, and a hard compaction pan can sometimes inhibit tillering and indirectly nodal root development. These plants may be pulled out during grazing which will impact subsequent feed and grain production.
If anchored, plants can be grazed as early as the three to four leaf stage. The earlier a crop is grazed, the more time there is for it to recover and avoid grain yield losses. However, there won’t be much feed or soil cover at this time, so it’s a compromise between this and the need for feed.
How much to leave behind
The lower a crop is grazed, the longer it will take to recover leaf area. This is because the less leaf material there is, the less interception of sunlight which reduces growth.
It’s recommended not to graze below the ‘white line’ (point where stem goes from green to white). However, if growers are facing a short growing season, it’s best not to graze so low – leave some green leaf.
Growers in areas that have a longer growing season can graze lower as they have more time for recovery.
Higher stocking rates will help achieve more-even grazing, reducing trampling, the risk of baring out areas and uneven ripening. Use of electric fencing and frequently shifting stock can help achieve this.
Grazing duration
If the crop is for forage only, rotationally grazing two to three times will keep the crop more nutritious (higher energy and protein, lower lignin) compared with set stocking.
If a crop will be used for hay or grain production, then graze early and less intensely; the earlier the better and not past GS30. Leave some green leaf to support the plant recovery process. Longer or later grazing, will delay maturity more than a short grazing period or early grazing. Early sown crops will recover best after grazing.
Animal health considerations
A change in diet and high water content may result in scours. To avoid this ensure the new feed source is introduced slowly and provide roughage such as hay for one to two days before introduction and continue while on the cereal crop.
Grazing green oats, wheat or rapidly growing grasses can induce milk fever (hypocalcaemia). This occurs when the body fails to mobilise enough calcium from the bones to maintain normal blood calcium levels. In cows it can be seen prior to and soon after calving. In sheep it is usually seen in ewes in late pregnancy but can be seen in all classes of animals.
Low magnesium (Mg) may result in grass tetany (cattle) or grass staggers (sheep), or subclinical deficiency, i.e. lower growth rates (hypomagnesaemsia) under more marginal deficiencies. It can be induced by increased body demands for Mg during late pregnancy and lactation, and pastures with low levels of Mg.
Wheat has high tissue levels of potassium (K), marginal Mg and low sodium (Na); the combination of high K and low Na reduces Mg absorption in the rumen. Oats do not have this problem. The jury is still out about the effects of barley on Mg absorption.
To prevent the above conditions provide a 1:1 mix of Causmag (MgO)/salt and sun cured hay.
If using Dolomite (CaMg(CO3)2) use a 3:1 Dolomite/salt mix and if animals are in late pregnancy or lactating use a mix of 2:2:1 Causmag/ground limestone (CaCO3)/salt to provide calcium.
The publication ‘Free Food for Thought’ discusses the effects of grazing crops on animal and plant production in more detail. Call BCG on 5492 2787 for your free copy.
