Antinutritional properties of wheat 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 allergies) 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).
Viscosity due to gluten and pentosans
Gluten becomes viscous in the presence of water, and while this property is highly desirable for flour processing, it can be dangerous to animals fed large amounts of wheat flour or finely ground wheat. Gluten was reported to form dough balls in the stomachs of pigs, blocking digestion and starving the animals to death (De Bry, 2001). In cattle and horses, finely milled wheat forms a paste-like mass in the mouth and the digestive tract which may lead to digestive upsets (Blair, 2011; Martin-Rosset, 2012). Durum wheat has a higher gluten strength and rolled grains have been reported to become pasty and sticky (Lardy et al., 2000).
Pentosans (among which arabinoxylans) are polymers of pentose sugars that increase diet viscosity and have an antinutritional activity in poultry. Varieties with low pentosan content should be preferred for poultry (Adeola et al., 2004; Choct et al., 1990).
Acidosis and other starch-related disorders
Wheat grain is rich in starch, which is fermented more rapidly than the starch in maize, resulting in a greater potential for digestive upsets, including acidosis, bloat, laminitis and reduced or erratic intake patterns (Fulton et al., 1979; Lardy et al., 2000). Wheat grain can cause acute acidosis if fed in large quantities to unaccustomed ruminants. The fermentation of large amounts of starch in the rumen lowers rumen pH, resulting in rumen stasis, a decrease in forage digestion, diarrhoea, dehydration and metabolic acidosis. If acidosis reaches the blood, it can cause heart failure, kidney failure and death. Acute acidosis occurs in ruminants that accidentally consume large amounts of cereal grains. When animals are progressively introduced to wheat grain in combination with hay, no particular problems occur even at high inclusion levels (Walker, 2006). The high starch content may also cause various digestive disorders in horses (Trillaud-Geyl et al., 2006; Martin-Rosset, 2012).
Mycotoxins
Wheat is susceptible to fungal diseases, notably by Fusarium species. Fusarium infection (Fusarium Head Blight, also called scab) occurs during flowering when the weather is warm and wet, 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 carcinogenic, 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 (USA) 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 exposure 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 also 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, allowing them to develop during storage, resulting in a production of ochratoxins and aflatoxins. It is important to store well-dried wheat grain (less than 14% moisture) at a temperature below 20°C. Pests should be prevented from entering the storage area as they increase heat and moisture, and favour fungal development (TIS, 2013; Birck et al., 2006). Sprouted wheat should be screened for aflatoxin if mold is present (Lalman et al., 2011).