Maize quality has to be carefully assessed, particularly as moulding and rancidity may occur rapidly after grinding.
Acidosis
Feeding ruminants with high-starch feeds may cause acidosis. The fermentation of large amounts of starch in the rumen lowers rumen pH, causing rumen stasis, a decrease in forage digestion, diarrhoea and dehydration, forerunners of metabolic acidosis. However, maize starch is not as readily fermentable as the starch of other grains such as barley and wheat, thus reducing the incidence rumen acidosis.
Mycotoxins
Maize is susceptible to various moulds producing mycotoxins that have deleterious effects on animal health. Grain quality must be assessed before feeding livestock, and tests exist to measure mycotoxin contamination (Herrman, 2002).
Aflatoxins are produced by Aspergillus flavus, which invades maize when drought or earworm stresses occur. Aflatoxins reduce growth and feed efficiency. They also cause liver disorders, abortion and are lethal to pigs at high levels. Aflatoxin M1 may contaminate milk from cows fed on damaged maize.
Deoxynivalenol is produced by Fusarium sp. infestations that occur when the weather is warm (25-30°C) and moisture is high. Signs of toxicosis are weight loss, lower feed conversion, vomiting, bloody diarrhoea, severe dermatitis, lower egg production in hens, abortion in mammals and finally death. Pigs are more susceptible to vomitoxin than cattle and poultry.
Zearalenone is produced by Fusarium graminearum and other Fusarium species in warm and moist conditions. It has deleterious effects on pig sexual characteristics (swollen vulva in sows, enlarged mammary glands in young pigs) and reproductive performance (embryonic death, lower fetal development, lower litter size).
Ochratoxin occurs when high moisture maize is infested by Aspergillus or Penicillium. It is thus recommended to store the grains in dry (less than 22% moisture) and cool conditions. Ochratoxin causes renal disorder in pigs and decreases growth, egg shell quality and egg production in poultry. Adding ascorbic acid may alleviate toxicosis in laying hens.
Fumonisins are typical of maize and are produced by Fusarium verticilloides and other Fusarium species. Fumonisins are carcinogenic in pigs and humans, and they cause pulmonary oedema in pigs. In horses, they induce leukoencephalomalacia (lower intake, lameness, oral and facial paralysis, seizure and eventual death). Ammoniation may reduce fumonisin levels.
Acid-resistant Escherichia coli
Cattle fed mostly maize grain had a lower colonic pH and more acid-resistant Escherichia coli than cattle fed only hay (Diez-Gonzalez et al., 1998).
Genetically-modified varieties
The potential health issues with GM maize and other GM foods is a matter of considerable debate. While most studies have failed to show deleterious side-effects to the use of GM maize (EFSA GMO Panel, 2008), these varieties remain controversial and subject to legal authorization in some countries.