Studies have shown a negative impact of deoxynivalenol, DON in laying hens, however results vary considerably between studies. Many scientific papers state that chickens are less sensitive to mycotoxins compared to other species.
So, should egg producers worry about DON in feed? The answer is, it depends. Here are some of the factors that need to be considered to assess the risk of DON in feed to the performance of laying hens and egg safety.
Factors determining the impact of DON in laying hens
Effects of DON on performance in laying hens varies considerably between studies. Whereas some studies report very little impact, other studies showed a significant impact of DON on laying rate/egg production, egg shell quality and weight gains in laying hens.
There are some factors that can explain the variance seen in results between studies examining the effect of DON on laying hens. Depending on the level of presence of these factors in the studies, the effect of DON on laying hen performance can be significant.
• Level of DON in feed and co-contamination with other mycotoxins
• Natural versus purified form of DON
• Length of exposure to DON in feed
• Stage of egg production
• Type of breed
Differences in toxic effects may be because some studies used artificially contaminated grain or a single source of contaminated grain. Artificially contaminated diets with purified DON are less toxic than naturally contaminated diets. This is mainly because the use of a blend of naturally contaminated grains increases the potential for other mycotoxins being present. Having multiple mycotoxins present can increase the effect of DON present as a result of toxicological synergies arising from interactions with the other mycotoxins. Egg production was negatively affected in hens fed a diet containing sorghum that was contaminated with zearalenone (ZON) at a level of 1.1 mg/kg and DON at a level of 0.3 mg/kg. The effect in this study was thought to be due to the synergistic effect of DON and ZON.
Longer periods of exposure to DON in the diet generally showed a greater impact on the performance of laying hens compared to studies where the hens were only exposed to DON for a few weeks. Another study comparing the effect of DON on laying hens between stages of production showed that DON had more of an effect in months 7-12, than in the first 6 months of production.
What is also of interest to note is that not all breeds of laying hens respond the same to DON. For example, a study comparing Lohmann Brown laying hens with LSL Lohmann laying hens demonstrated that Lohmann Brown laying hens are more sensitive to DON.
Underlying mechanisms for negative responses
Chickens are less sensitive compared to other species. This can be attributed to differences in DON absorption, distribution, metabolism and elimination. Nevertheless, there are still studies that have shown negative effects on laying hen performance. This has been attributed to some extent to a reduction in feed intake in association with DON in diets. Other studies have indicated that DON has an influence on intestinal morphology of chickens and nutrient absorption (glucose and amino acids), which can reduce nutrient efficiency of laying hens. For example, it was shown that DON can alter the structure of the duodenal and jejunal mucosa in the form of shorter and thinner villi.
Disease susceptibility in response to DON in feed
DON has been shown to impair immunological functions in chickens. The impact of DON on the immune system ranges from immunosuppression to immunostimulation, according to its concentration, duration and time of exposure.
An important immunotoxic effect of DON in diets for laying hens is the reduction of white
blood cell and total lymphocyte numbers. On top of that low doses of DON upregulate the expression of inflammation related genes and proinflammatory cytokines.
DON is shown to suppress the antibody response to infectious bronchitis vaccine (IBV) and to Newcastle disease virus (NDV) in laying hens (3.5 to 14 mg of DON/kg feed), respectively.
The dysregulation of the immune system together with the negative impact of DON on gut function can lead to increasing the susceptibility of poultry flocks to infectious diseases.
Does DON in feed pose risks for egg safety and human health?
DON can cause health problems such as nausea, gastrointestinal upset and diarrhea in humans. Therefore, it is important to ensure that it is not transmitted from chicken feed into eggs at a rate that can cause health risks for humans.
A 2018 study from China looking at mycotoxin levels in eggs in three different areas in China (Jiangsu, Zhejiang, and Shanghai) reported DON, 15-AcDON, and Zearelone as the most frequently observed mycotoxins in eggs. The highest levels of contamination were noted in Shanghai with up to 50% testing positive. Subsequent risk assessment for humans concluded that the risk of causing problems to humans in all three areas was low based on the levels of mycotoxins that were found in eggs and normal egg consumption. The DON intake through eggs was still below the provisional maximum tolerable daily intake. However, the study did highlight the need to monitor DON in feed and to restrict permitted levels of DON in feed.
Scientific studies looking at the carry-over effect of DON from feed to eggs in laying hens concluded that the carry-over effect of DON into eggs is very low. Such that providing that the DON level of chicken feed does not exceed current guidelines (5ppm) there is certainly no health risk to humans.
A very recent study carried out in 2019 demonstrated that DON occurs mainly as its non-toxic metabolite DON-3Ss in eggs from laying hen fed DON contaminated feed.
Video: How does the mycotoxin DON affect the performance of laying hens?
Please see second half of this video.