Crop residues play an essential role in the maintenance and accumulation of organic matter in the soil. It also helps combat soil erosion.

Estimated reading time: 6 minutes

Once harvesting in the summer planting areas has been completed, it is a good time to move your animals onto the crop residues remaining in the fields. During the winter months, crop residues are very effective in bridging the autumn/winter gap in the fodder flow programme, as it is a very economical way of feeding animals.

Dr Josef van Wyngaard, technical manager at Voermol Feeds, says that nowadays a lot of emphasis is placed on conservation farming and diversity, making crop residues an excellent supplement that can be applied in a crop farming enterprise’s added livestock branch.

“Since livestock utilise only 15 to 40% of these crop residues, more than half remains on the fields for the maintenance and accumulation of organic matter in the soil. This will also combat soil erosion. Around 20% of the material of non-grazed crop residues will be lost to wind and weathering during winter,” he explains.

Due to its good nutritional value and the fact that it can be planted on a large scale, the most popular crops for crop residues are maize, soya beans and groundnuts.

Other crops can also be utilised and include various legumes, brassica crop residues such as cabbage and cauliflower, and even whole vegetables such as carrots, potatoes and tubers which can be incorporated into a fodder flow programme. However, maize, soya beans and groundnuts remain those commonly used.

Each crop has advantages but also disadvantages in the sense that it can lead to nutrition-related metabolic disorders if not managed properly. Acidosis is the major culprit if animals on crop residues are not managed correctly.

Dr Johan van Rensburg of ABE Biotech says maize forage is very popular for finishing or overwintering sheep due to its high energy content, especially if a lot of grain is left on the ground during harvesting.

According to him, one of the advantages of maize forage is its higher yield and carrying capacity compared to other cultivated dryland pastures. It fits in well with fodder flow planning for autumn and winter. Maize residues can sustain animals for up to three months.

Although it is an excellent source of nutrition, maize does pose disadvantages such as its lower protein value and a tendency to be selenium, zinc, manganese and copper deficient.

“This leads to bloat in lambs. The minerals (Ca:P ratio) are not balanced, and the excess phosphorus leads to the formation of bladder stones in wethers and rams, especially if they run on maize forage for more than 75 days.

“A suitable lick containing the necessary protein, trace minerals and medicine to prevent acidosis and the formation of bladder stones is a possible solution. However, if the lick contains urea, sheep must be adapted before they start grazing the maize,” he says.

Soya remains a firm favourite

Soya bean residues are also a firm favourite and are utilised quite readily in the western summer planting regions of South Africa.

Johan Mouton, technical manager of research and development for ruminants at RCL Foods’ Molatek, says soya residues make a valuable contribution to fodder flow planning. Soya bean residues are normally available from April and, depending on the yield, sheep can remain on soya bean residues for six to nine weeks.

Running seven to eight dry sheep or one head of cattle per hectare over a period of eight weeks is a good guideline. “Normally, animals on soya bean residues put on weight up until around eight weeks, after which they begin to lose weight.

“The best value is derived from residues that are grazed as quickly as possible after the soya beans have been harvested. The biggest problem is metabolic disorders, which requires active management. Supplementing roughage to improve the value of soya bean residues is very effective, especially in sheep,” he says.

As with maize residues, adding a lick to the soya residues goes a long way in managing general nutrition-related problems, but the lick must be urea-free when given along with soya residues.

Crop residues are a good source of nutrition for sheep and the ideal means of bridging the autumn/winter gap in the fodder flow programme.

Crop residues and animal health

Experts agree that acidosis can be the biggest problem when utilising crop residues. Dr Van Wyngaard says acidosis is often attributed to the excess starch the animals ingest.

Other problems which can also arise are:

  • Bladder stones due to the excess phosphorus the animals ingest when grazing maize crop residues.
  • Legume crop residues have a high level of soluble protein which causes bloat.
  • Prussic acid poisoning due to the regrowth of plants after late rains and high temperatures.
  • Iodine deficiency can occur when brassica crop residues such as cabbage and cauliflower are grazed for long periods.
  • A deficiency in trace minerals such as manganese, zinc and copper, as well as vitamin A can occur.
  • Although not common, animals can choke on maize cobs and whole vegetables such as carrots, potatoes and tubers.

However, Dr Van Wyngaard emphasises that these potential risks can be avoided with correct management and lick supplementation.

Management and control

As with all other aspects of farming, a solid management strategy is necessary to achieve success with crop residues. There are a number of useful tips to be given, but the most crucial one is that animals must be adapted to the residues gradually.

Dr Van Rensburg offers some practical tips for managing animals on crop residues. Just like in a feedlot, lambs must receive the necessary vaccinations timeously, especially those against pulpy kidney and Pasteurella. Internal parasites such as wireworm and milk tapeworm, as well as external parasites such as blowflies and ticks, also need treating.

“Animals that develop acidosis must be removed and treated with an antacid. Baking soda can be used in the early stages of acidosis. Dose with two tablespoons of baking soda dissolved in 200mℓ of water. To prevent the absorption of toxins from the rumen and intestinal tract, dose with activated carbon. Prevent liver abscesses by injecting the animal with penicillin,” he explains.

It is also advisable to inject animals with vitamin B complex to support the liver in processing toxins and acids. Furthermore, sick animals that have been removed from residues must be readjusted. He advises using lucerne hay, which is an excellent source of roughage, and adding a steady supply of maize so that animals can return to the fields without delay.

Another tip is to keep herds and flocks as small as possible, as this will simplify management. “Place older animals with younger ones to teach them how to graze crop residues. The milk production of wet ewes on forage maize is also higher and their lambs will experience less weaning shock,” he says. – Koos du Pisanie, Stockfarm

Read about how to adapt livestock on crop residues.

For more information, phone
Dr Josef van Wyngaard of Voermol on 082 336 0626,
Johan Mouton of Molatek on 083 278 7746,
or Dr Johan van Rensburg of ABE Biotech on 082 336 5498.