Potential sheep health problems
Sheep which have sudden access to high levels of field pea seed are susceptible to acidosis (grain poisoning) and enterotoxaemia (pulpy kidney).
Field pea seed is similar to cereal grain and different to lupin seed in that the carbohydrate portion is in the form of starch. The sudden introduction to starch diets causes grain poisoning in sheep and cattle due to the rapid conversion of starch to lactic acid by rumen organisms.
Field experience and trials show that seed intake for sheep on conventional trailing field pea stubble can exceed the 500g per head per day required to cause grain poisoning. If grain poisoning occurs, the sheep will scour and lose weight for the entire grazing period, and the nutritional benefit of the paddock will be lost. In severe cases, sheep may die.
Sheep can be preconditioned to starch by grazing cereal stubble which is high in grain or by undergoing a cereal grain introduction period before grazing field pea stubble. This allows micro-organisms in the rumen to become accustomed to starch and prevents grain poisoning.
Enterotoxaemia or pulpy kidney is caused by a toxin produced by the bacteria Clostridium perfringens (type D). The organism is resident in the gut of sheep and can proliferate on high sugar or starch diets, such as field pea grain. Enterotoxaemia is common in sheep grazing cereal stubble as well as field pea stubble. Sheep should undergo a vaccination program at least ten days before grazing field pea stubble. Consult your local district veterinarian.
The best time to graze
The best time for grazing depends on soil type, geographical location and other feed sources on the farm. If the aim of grazing is to reduce pea weevil numbers, stubble must be grazed as soon after harvest as possible.
On medium and heavy soils in the central Wheatbelt, or areas where strong winds are not likely in November and December, grazing should occur straight after harvest. The paddock should be inspected regularly and stock removed if necessary. In the Great Southern and South Coastal regions, or areas where strong winds are likely in November and December, grazing straight after harvest is not recommended.
Soils that have a weak crust are best grazed later in autumn just prior to seeding. Grazing may be used to break down the field pea vine and residues to help seeding. This late grazing exposes the paddocks for a short time and limits the chance of erosion.
Sandy soils should not be grazed at all, except when summer rains have caused weeds to germinate.
Good feed in autumn is more valuable than feed in early summer because most dry feed deteriorates during summer due to weathering. This is particularly so for autumn lambing ewe flocks because of their high energy needs during lactation.
Grain in stubble does not tend to deteriorate as quickly as leaf and stem components, although it can be buried if significant summer rain occurs. Grain may provide a good source of feed after pastures have deteriorated during summer, or for finishing out-of-season lambs. If, however, summer rain occurs and produces a germination, the feed value of the paddock may be enhanced by allowing a green pick to establish.
The no-grazing option:
- Less potential for wind erosion and soil loss
- May give additional yield and protein improvements in following cereal crops
- Varieties of semi-leafless field pea may have very low harvest losses which do not warrant grazing.
The grazing option:
- Only for a short period, as most available spilt grain is consumed in about four weeks or less if the harvester is well set up or if a semi-leafless sugar pod field pea variety is grown
- Gives good liveweight gain in weaner and adult sheep with low worm burdens, during the short period that seed is available
- Greatly increases the chance of wind erosion in most situations unless carefully managed.
- Not recommended on sandy or fragile surfaced soils
- Breaks down vines which helps seeding.