Storage proteins
Wheat storage proteins (albumins, gliadins and glutenins) also act as chemical defences against pathogens and phytophagous animals. Gluten, a protein composite of gliadin and glutenin, is known to cause digestive disorders in gluten-sensitive humans. Other digestive diseases (including allergy) have been linked to gliadins. Wheat albumins are reported to have an anti-amylase, anti-tryptic and anti-lipase activity in some animal species (De Bry, 2001).
Gluten becomes viscous in the presence of water, and while this property is highly desirable for flour processing, it can be lethal to animals fed large amounts of wheat flour. Gluten was reported to cause dough balls in the stomachs of pigs, blocking digestion and starving the animals to death (De Bry, 2001).
Pentosans
Pentosans (among which arabinoxylans) are polymers of pentose sugars that increase diet viscosity and cause antinutritional activity in poultry (Adeola et al., 2004; Choct et al., 1990).
Mycotoxins
Wheat, like barley and other cereal grains, is susceptible to fungal diseases, notably by Fusarium species. Fusarium infection occurs during flowering when the weather is warm and wet (fusarium head blight, also called scab), or during storage when the grain is not stored properly. Fusarium diseases are a major source of grain losses. In Argentina, several Fusarium epidemics of varying severity have occurred in the past 60 years in the Central-North wheat production area, where yield losses were estimated to average between 20 and 50% (Stenglein, 2009). In China, severe epidemics of fusarium head blight have affected more than 7 million ha of wheat and caused yield losses of more than 1 million t (Leonard et al., 2003).
Fusarium infections produce deleterious toxins called trichothecenes (T-2 and HT-2, deoxynivalenol (DON), zearalenone) that have cancerogenic, neurologic, haematologic and digestive (vomiting) effects in animals and humans. Regulations differ from one country to another and from one animal species to another. The FDA advisory levels for DON in wheat grain and grain by-products (not including distillers grains and brewers grains) are listed below (FDA, 2010):
| |
DON (in 88% DM product) |
| Animal |
Wheat grain and by-products |
Ration |
| Ruminating beef and feedlot cattle older than 4 months |
10 ppm |
10 ppm |
| Ruminating dairy cattle older than 4 months |
10 ppm |
5 ppm |
| Chickens |
10 ppm |
< 50% grain in the diet |
| Pigs |
5 ppm |
< 20% grain in the diet |
In Europe, EFSA has stated that the estimated exposures to the sum of T-2 and HT-2 trichothecenes based on the available occurrence data are considered unlikely to be a health concern for ruminants, rabbits and farmed fish. For pigs, poultry, dogs and horses the risk of adverse health effects is low (EFSA, 2011).
Post-harvest fungal infections also cause mycotoxin contamination. In addition to Fusarium species, Aspergillus and Penicillium fungi benefit from elevated moisture and heating to develop during storage, resulting in production of ochratoxins and aflatoxins. It is important to store well-dried wheat grain (less than 14% moisture) at temperature below 20°C. Pests should be prevented from entering the storage area as they increase heat and moisture and favour fungal developments (TIS, 2013; Birck et al., 2006).
