|dc.description.abstract||Fusarium mycotoxins, such as deoxynivalenol (DON), are ubiquitous contaminants of cereal grains. When Fusarium-damaged grains are used in feeds, DON and other mycotoxins are a potential health risk to poultry with adverse effects, such as reductions in feed intake, growth, and feed efficiency and increased disease susceptibility. With increasing prevalence of Fusarium-contaminated grain worldwide, growing demand for high-quality protein like poultry, and a shift to antibiotic-free poultry production systems, it is important to re-evaluate threshold concentrations for Fusarium mycotoxins in poultry diets that are reflected in the current guidance values. Therefore, five animal feeding trials were conducted to better characterize sub-lethal responses to Fusarium mycotoxins (primarily DON) in broiler chickens and understand how exposure factors affect broiler responses to contaminated diets. For all trials, experimental diets were prepared with a source of clean wheat (< 0.5 mg/kg DON) or naturally Fusarium-contaminated wheat (~ 11.4 mg/kg DON) reflecting diets that would be encountered in broiler production.
In the first study, the effects of timing and duration of exposure to contaminated diets on growth performance and intestinal mucosa structures were examined in a 34-d feeding trial. Starter diets (0.41 and 6.62 mg/kg DON), provided from 1 to 21 day of age (d), and grower diets (0.54 and 7.90 mg/kg DON) provided from 22 to 34 d. Birds fed the DON-contaminated diet over the first 14 d did not exhibit any changes in growth performance; however, growth suppression was observed in the birds fed DON-contaminated diets during the grower phase. Histopathological analysis of the ileal region revealed that birds provided the DON diets throughout the entire trial (1 to 34 d) had shorter villi and shallower crypt than control birds. Based on these results, the grower phase was targeted for the second study where two trials were conducted to determine the effect of short-term exposure (7 days, 21 to 27 d) to DON-contaminated diets on feed preference and feeding behaviour. Three wheat-based experimental diets (control, low and high DON) were prepared and contained 0.14, 2.27 and 5.84 mg/kg DON, respectively. In the preference trial, birds were randomly assigned to one of the three diet pairs (control vs. low, control vs. high and low vs. high DON). In the feeding behaviour trial, birds were randomly assigned to one of the three treatments and received either control, low or high DON diets. The activity of birds was recorded for three 1-h periods daily and birds’ behaviour at the feeder was observed. In the preference trial, broilers preferred the control diet over low or high DON diets. There was no preference indicated between the low vs high DON diets. Behavioural observations revealed that birds fed the DON diet spent more time at the feeder as compared to controls during the observation periods. In the third study, a 28-d pair-feeding trial was conducted to determine whether the performance and gastrointestinal effects of Fusarium mycotoxins (primarily DON) are due to a DON-induced reduction in feed intake. Birds were fed either DON-contaminated diets (2.4 to 3.0 mg/kg) or control diets (< 0.1 mg/kg DON). The amount of control diet provided to the pair-fed birds was based on feed consumption of DON treatment at the similar age. During the starter phase, DON-fed birds consumed less feed than control birds while during the grower phase, DON-fed birds had lower feed intake and weight gain than control birds. The pair-fed birds had lower feed intake and weight gain compared to DON-fed birds during the starter period and did not differ during the grower period. Since DON-fed birds and restricted-fed birds with similar (reduced) feed intake had equally suppressed performance, the contribution of dietary DON to growth suppression in broilers is considered independent from other toxic effects of DON. In the final study, a 32-d feeding trial was conducted to determine the efficacy of a yeast cell wall-based feed additive in counteracting the performance effects of mycotoxins in broilers fed a naturally DON-contaminated diet (1.8 to 2.0 mg/kg). The DON-contaminated diet depressed growth performance, while supplementation of the feed additive increased feed intake, weight gain and body weight in birds when included in contaminated diets during the grower stage.
Overall, there was a consistent reduction of feed intake, weight gain and feed efficiency in response to low to moderate concentrations of DON-contaminated diets across the individual feeding trials conducted in this research. Broiler chickens are apparently more sensitive to DON-contaminated diets than previously estimated particularly during later stages of growth. In addition to the performance effects, DON contamination reduces diet palatability and alters broiler feeding behaviour. Although difficult to confirm based on current data, reduced feed intake in broilers is most likely caused by DON-induced sensory aversion and/or anorexia. Based on results of this research, it is recommended to reevaluate the current 5 mg/kg threshold concentrations for DON for poultry to help protect birds from sub-clinical mycotoxin concentrations that can challenge poultry production.||