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Risks of Using Over-Wintered Crops as Livestock Feed

By: Murray Feist, M.Sc., P.Ag, Ruminant Nutritionist, Saskatchewan and Barry Yaremcio  M.Sc., P.Ag. Beef and Forage Specialist, Alberta

April 2017

Using over-wintered cereal crops for swath grazing this spring or baling for use as greenfeed next fall and winter, are two options to utilize last year’s crop for ruminants. Threshing the crop and feeding the grain to monogastrics and ruminants is also possible. There are a number of concerns associated with feeding over wintered crops to both types of livestock. 

Does the forage or grain meet nutritional requirements of the animals?  

Crops become weather damaged when left out over winter. Typically, protein and energy contents are lower in the spring compared to the fall.  Digestibility of the feeds can be reduced, as well. In the case of greenfeed or swath grazing, digestibility could be 10 per cent lower. This further reduces the suitability of unthreshed crops or spring threshed grain if it is to be the major component or sole ingredient in a ration. They will need to be blended off with other feedstocks to make up for the loss in quality.

Animals in late pregnancy or in lactation have approximately 25 to 30 per cent higher nutrient requirements than animals in early or mid-pregnancy. While there are differences between species, this trend is true for all and therefore spring swath grazing or cereal greenfeed harvested from these crops need to be tested for quality and rations balanced to meet requirements. 

Mycotoxins and overwintered crops 

Mycotoxins can be found in many cereal grains (wheat, barley, rye, etc.), and corn.  Mycotoxins are much less common in crops such as canola and legumes (peas, soybeans, faba beans etc.). The fungi that have the potential to produce mycotoxins predominantly infect the seed head and not the stems or leaves of the plant.  

Ergot is produced by the fungal species Claviceps. Fusarium, another fungus, also infects crops early in the growing season. Moulds develop in the seed heads over the summer and mycotoxins are formed in the developing crop. If the weather is reasonably mild with high relatively humidity, conditions are ideal for mycotoxin development. Ergot concentrations appear to reach maximum values by mid to late July.  Levels remain stable for ergot, while levels of some of the Fusarium mycotoxins can increase when grain is in storage.

For crops that remain out in the field, such as for swath or corn grazing, microbial activity stops when temperatures drop below 5 degrees Celsius, which locks existing mycotoxin levels into the crop over winter. These same microbial levels are present in the crop going into spring.

Nutritional quality of the greenfeed or grain is a big concern. If feed test results indicate that there is sufficient quality to feed to livestock, then testing for mycotoxins is required before any of the material is fed to livestock. 

Spring threshed crops 

Spring threshed cereal crops may contain ergot, fusarium, moulds, dirt and fecal contamination. Any problem that was present in the crop last fall will be there in the spring. Freezing temperatures during the winter stopped further microbial development. In the warmer temperatures last fall, there was a risk that mycotoxins produced by various moulds and fungi. These could be harmful to all classes of livestock. Before feeding a salvaged spring threshed cereal grain or greenfeed, it is advisable to have the feed tested for nutrient content and screened for mycotoxins.  

Silaging over wintered crops 

Ensiling is the process of controlled fermentation to preserve wet forage material to a stable feed source. Salvaging overwintered feed by ensiling is not recommended. 

There are two stages of fermentation during the fermentation process. Understanding the process helps explain why ensiling an overwintered crop is not an option:

  1. The first stage involves aerobic respiration because oxygen is present. When plant material is first chopped and put in a pit, bag or bale, oxygen is present: bacteria use up available oxygen and plant sugars. Carbon dioxide and heat are produced. A shorter aerobic stage produces less heat and uses less soluble sugars resulting in higher quality silage.
  2. The second stage follows in an anaerobic environment when all the oxygen is used up within the sealed pit, pile or bale. Anerobic bacteria use plant sugars to increase their populations to produce lactic acid which lowers the pH of the silage allowing the preservation or “pickling” to occur. The entire process typically takes 3 to 4 weeks to complete and requires a minimum of 6 to 12 per cent plant sugars in the material to ensile effectively.

Overwintered cereal crops should not be chopped or baled to make pit, pile or bale silage because it may not ensile properly. The over-wintered plant material would have been wetted and dried repeatedly resulting in leaching of soluble sugars and proteins out of the plant material. Without adequate amounts of sugars, microbe populations die off and fermentation does not occur. 

It is very unlikely that over-wintered corps will have adequate moisture to create a good environment for proper fermentation. For proper fermentation with chopped silage the recommended moisture content is 60 to 65 per cent and for bale silage 45 to 50 per cent. If moisture levels are lower than this, it is very difficult to pack the material in a pit or pile resulting in higher oxygen content, longer fermentation and possibly lower quality silage. In bale silage, the drier material will not pack in the bale and the desired fermentation may not occur.   

There’s no point going to the expense of making silage only to find a marginal to poor quality product that may not be suitable for use.

Baling crops 

Over-wintered forage must be dry before baling. Bales with a moisture content more than 16 to 18 per cent have the potential to heat and lose quality. During the heating process some of the sugars (or energy) will be used by the microbes thereby reducing the energy content in the feed. If temperatures within the bale get above 40o C, the bales will smell sweet or like tobacco. The colour can change to dark brown or black. When this happens, a portion of the protein will be bound to the plant fiber and not available to the animals. If this occurs, request for an Acid Detergent Insoluble Nitrogen (ADIN) or ADIP (protein) test in addition to the regular feed analysis. Use the adjusted lower protein value when formulating rations.

Raking or inverting over-wintered crop windrows in low areas of the field, or where the crop has dropped through the stubble helps with the drying process. It also helps to get more uniform moisture content in the material going into bales. This process should be done at lower speeds to prevent grain heads from breaking off the stems. If dirt is kicked up into the crop material and moisture levels higher than anticipated, white mould can form in the bales.

Moulds can develop in greenfeed bales that have a higher moisture content. A loss of quality is possible and feed refusal increases. If mould is present, bales should be rolled out rather than fed in a bale feeder. This will allow the cows to sort through the feed and allow them to waste the material that is contaminated with mould. Forcing cows to eat 5 per cent moldy feed can potentially reduce ration digestibility by 10 per cent. Rolling out the greenfeed also reduces the amount of dust and spores the animal breathes in reducing the risk for eye and respiratory problems. 

Human health concerns when using over-wintered crops 

Operator health can be impacted by harmful components that may be present in over-wintered crops.  Take the necessary precautions to prevent health issues.

  • If mice are present in the field, swaths can be contaminated by manure and urine. Hanta virus is a concern to humans, but not to pets or livestock. Inhaling dust contaminated with rodent droppings, urine or saliva, or infecting open wounds with the dust can create serious health problems for the producer. Problems are more likely when working with threshed grain in bins, but it can also be a problem with greenfeed bales. 
  • Molds, dusts and spores found on the grain and forage components can be released into the air when bales are moved or handled. Respiratory problems and eye irritation are concerns.
  • Dust from ergot contaminated grain can cause irritation in the upper respiratory tract. 

Feeding Considerations  

When feeding ruminants mature cereal crop greenfeed, there are many problems that can occur. Grain overload, acidosis, and bloat may occur in cattle and sheep because the weight ratio of grain to straw in this material is approximately 1:1. The animals prefer to eat the grain rather than the straw.

Macro mineral imbalances of calcium, phosphorus, magnesium and potassium could cause downer cows or milk fever.     

Sheep require very high quality forages in late pregnancy and after lambing. Lower quality forages such as over-wintered cereal greenfeed or spring threshed grain generally do not have the quality required to meet requirements. It is not recommended to use this type of feed. 

Monogastric animals are very sensitive to mycotoxins especially DON and Zearalenone. Levels of vomitoxin (DON) at 1 ppb will cause feed refusal in pigs. 

Spring threshed grains could contain waterfowl manure. With the significant risk of Avian Influenza being spread, spring threshed grain should not be used in any poultry diet. 

Ergot contaminated grain is a concern for all types of livestock. Any feed containing ergot must be tested for mycotoxin levels before being included in rations.

For additional information 

Contact a nutritionist, government livestock extension specialist, veterinarian, feed salesmen or consultant that can provide assistance with feeding over-wintered crops to livestock.

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