Stefaan VAN DYCK
Kemin AgriFoods Europe
By Courtesy of Kemin AgriFoods Europe
Introduction
The worldwide occurrence of mycotoxin contamination of feedstuffs and the severity of mycotoxicoses in farm animals shows a tendency to increase in recent years. Many factors contribute to this increase such as the global climate change and increased international trading of feeding stuffs from different geographical origins. Blends of various raw materials in compound feed increase the risk of feed contamination with several mycotoxins. Furthermore, the toxic effect of any single mycotoxin may be amplified due to synergistic interactions between different contaminants.
The use of mycotoxin binders is an established practice in many parts of the world for the reduction of myctoxin-related risks in animal production. Currently, a variety of approaches are being used to assess and demonstrate the efficacy of a wide variety of mycotoxin inactivators. Most differences appear in the in vitro studies due to the diversity of the proposed modes of action. On the other hand there are also numerous ways in which the in vivo activity is demonstrated. This of course may create some confusion for the end users of the binders because one may expect that there should be a common ground for the evaluation of mycotoxin binders in animals.
The objective of the present overview is to summarise the requirements to unambiguously demonstrate in vivo mycotoxin binder performance in order to allow correct comparison of available trial data.
In total seven requirements are proposed to prove mycotoxin binder performance:
- Availability of essential nutrients to the animal
- The binder is not a growth promoter. Growth promotion may mask mycotoxicosis
- Improvement of zootechnical performance
- Recovery of organ status
- Excretion of mycotoxins via faeces
- Broad-spectrum mycotoxin binding performance
- Recovery of the immune status
Toxin binder performance study
The importance of all seven requirements will be discussed in detail. Examples will be given based on a comprehensive evaluation of an activated clay-based mycotoxin binder (Toxfin).
A total of 192 sexed Vencobb broilers (day-old) were randomly distributed among 4 groups with 4 replicates (2 males x 2 females). The birds were housed in cages for 35 days under similar experimental conditions and maintained with water and a corn-soya based mash feed available ad libitum. The experimental design is given in Table 1.
The overall performance of broilers at day 35 is shown in the Table 2.
Mycotoxin binder performance: nutrient binding
In general mycotoxin binders are perceived to possibly reduce animal performance due to nutrient binding. Of course this is a valid concern because 'unselective' binders might bind a broad range of mycotoxins, but also a wide variety of nutrients. Therefore a nutrient binding study is essential. Besides in vitro binding studies of e.g. vitamins and minerals, also the performance data are invaluable.
The control group with the mycotoxin binder, but no mycotoxins (treatment 2) should be included in any trial to check whether or not the binder also binds essential nutrients, which could result in diminished growth. This group should show similar weight gain and FCR as that of positive control treatment 1 in order to prove that the toxin binder does not bind essential nutrients such as vitamins, minerals and amino acids. Table 2 shows that the binder, without mycotoxins presence, has no negative effect on zootechnical performance.
Mycotoxin binder performance: growth-promoting effects
This parameter is strongly linked with food safety. When a mycotoxin binder has a growth promoting effect it might compensate for the negative effect caused by the mycotoxins without really preventing absorption and deposition of mycotoxins.
In the animal trial presented, treatment 2 was also used to identify an undesirable growth promoting effect. The effect would appear in case a better bird performance is observed in comparison with treatment 1. The binder in the diet free from mycotoxins did not show growth promotion since it was developed to be selective towards a wide range of mycotoxins only.
Mycotoxin binder performance: zootechnical performance recovery
Bird performance in the negative control group (treatment 3) was significantly worse than the basal diet in terms of body weight gain, FCR and mortality. A full recovery of weight gain and feed conversion was observed for the group that received the mycotoxin cocktail in the diet with additional Toxfin supplementation (1455 g and 1.76 vs. 1581 g and 1.57 respectively). The observed numerical differences were also statistically significant (Figure 1).
Feed consumption was approximately at the same level in all treatments varying within ~3% between the highest level of 2557 g observed in treatment 3 and the lowest 2486 g in treatment 4 with mycotoxins and including Toxfin.
Additionally, the liveability of chicks in treatment 3 was reduced by the mycotoxins causing 8% mortality. In contrast, the treatments 1, 2 and 4 showed only 2-4% mortality, which corresponds to the normal rate. Thus, Toxfin in treatment 4 reduced the negative impact of mycotoxicosis on zootechnical performance and improved chicken liveability.
Mycotoxin binder performance: organ status recovery
A clear sign of mycotoxin absorption in the animal is the damage caused to organs. Again this is a parameter fundamental for food safety as it indicates absorption of important levels of mycotoxins and possible deposition in animal products that will be used for consumption.
The relative weights of the 32-day old chickens' liver and kidney as a percentage of live weight are shown in Table 3.
Liver weight is the most sensitive indicator of mycotoxicosis. The liver weight of the mycotoxin treatment 3 was significantly increased by 0.78% as absolute or 40% as relative dimension comparing to control (2,74 vs. 1,96%). A significant reduction in liver relative weight was found in broilers that received the mycotoxin binder supplementation. Also the visual evaluation of the liver (Figure 2) confirmed that Toxfin successfully eliminated mycotoxicosis due to the binding of the different mycotoxins, which makes them unavailable for absorption through the gut wall.
There was also a clear negative influence of mycotoxins on kidneys. The group including only mycotoxins (treatment 3) showed 0.85% of kidney weight whilst in the control group and treatment with Toxfin the kidney weight was 0.62 and 0.63%, respectively. The most appropriate explanation of negative impact of the mycotoxin cocktail on kidney weight within the present study can be attributed to the known neuropathological effects of ochratoxin A and citrinin. In general the visual observation should be confirmed by the evaluation of histological samples from the organs.
Mycotoxin binder performance: mycotoxin excretion and broad-spectrum mycotoxin binding
In order to evaluate the mycotoxin-binding power of Toxfin, a balance study was conducted. Mycotoxin levels in the excreta were analysed and compared with levels given to birds through the feed. Results are shown in Table 4. Only about 30% of mycotoxins were excreted in treatment 3. It means that ~70% of the mycotoxins remained in the chicken, apparently available for absorption and retention in animal products. In the group fed mycotoxins + Toxfin the majority of the toxins were excreted.
Overall binding performance of the activate clay-based toxin binder used in this study was ~76%. Consequently only ~24% of the mycotoxins could not be recovered, probably due to metabolisation by microorganisms, rather than absorption. This conclusion is based on the fact that it is known that several microorganisms are able to metabolise mycotoxins. Also the visual evaluation of the organs indicates only minimal absorption of mycotoxins.
Mycotoxin binder performance: immunological parameters
Although organ and faecal excretion data are strong parameters of a strongly reduced absorption of mycotoxins in the gut, there is still a risk of small levels of certain mixtures of mycotoxins may still interfere with other health parameters such as immunology.
The possible negative impact of mycotoxins on the immune status of the animals was studied via the efficacy of Newcastle Disease vaccination. Antibodies against the viral protein responsible for haemagglutination can prevent haemagglutination. This principle is used as the basis for the haemagglutination-inhibition test (HI). The HI titre value was found to be the lowest in the mycotoxin fed group (Table 5), which indicates that vaccination was not successful. Addition of Toxfin to the diet levelled the HI titre value in the treatment 4 to the control mean.
Conclusions
Demonstrating the efficacy of a mycotoxin inactivator consists of much more than only a narrow look on zootechnical performance. Animals might still absorb mycotoxins when a binder is used that masks the negative effects due to a growth promoting effect.
As a consequence additional data is required on the organ status, the excretion of mycotoxins and the immunological status of the animal. Also suitable treatments should be introduced in the trial protocol in order to evaluate possible nutrient binding of unselective mycotoxin binders, which do not distinguish between toxins and nutrients.
The animal trial presented shows that even with a few additions to a standard testing protocol a significant amount of additional information can be gathered. This will assist the comparison of different products and help to assess the effect of mycotoxin binders on animal performance and food safety.
It is clear that complying with the seven requirements is essential to prove that a mycotoxin inactivator truly has a positive impact on the reduction of food safety risks caused by mycotoxins.
Results of the present study showed that requirements for the accession of mycotoxin binder performance were met by activated clays based product Toxfin.
