@phdthesis{8750228,
  abstract     = {{Mycotoxins are secondary metabolites produced by particular molds (fungi) that occur naturally in food and feed. Mycotoxins can be a source of various negative health effects and can be a significant health danger to livestock and humans. Aflatoxins are considered as the most important mycotoxins because of their carcinogenicity and their high prevalence. Nonetheless, chronic exposure to low concentration of aflatoxins can cause deleterious effects on performance in a variety of farm animals including poultry. To overcome the negative effect of mycotoxins, various strategies are being used. Adding mycotoxin binders to the feed is probably the most common post-harvest mitigation approach. Binders aim to adsorb mycotoxins to their surface in the gastro-intestinal tract forming a binder-toxin complex which is removed with the excreta. Mycotoxin binders may indeed also adsorb nutrients, micronutrients and veterinary drugs. Among the mycotoxin binders, clays are known to have promising adsorbing characteristics and are used as feed additives to overcome the negative effects of mycotoxicosis in livestock farming. Modification of clay minerals by heat treatment, known as calcination, can modify their physicochemical characteristics, thus enhance their adsorption characteristic. At the start of this PhD thesis, little was known about the effect of calcination on  mycotoxins binding. 
The General Introduction of this doctoral thesis highlights the risks associated with mycotoxins in animal feed. Both the exposure and toxicokinetics of aflatoxins (AFs) and zearalenone (ZEN) are discussed. Then, an overview of the legislation and pre- and post-harvest methods to decrease the impact of mycotoxins on animal health and performance are presented. The second part of the introduction is devoted to mycotoxin binders, with a focus on the diversity, structure and physicochemical properties of clay minerals. Furthermore, an overview of the modified clay is given, with a specific attention to the modification of clays by calcination. Finally, the possible negative effects of the clay supplementation to animal feed are discussed.   
The General Objective of this dissertation is to study the physicochemical characteristics of a Tunisian montmorillonite (MMT) clay before and after calcination and to investigate the effectiveness and safety of the calcined MMT clay in broilers feed.
In Chapter I, the physicochemical properties of Tunisian MMT clay before and after calcination at 550°C were studied. Then, an in vitro model that mimics the pH conditions of the monogastric gastrointestinal tract was used to evaluate the binding efficacy of the binders when artificially mixed with AFs and ZEN. After heat treatment, some changes in the mineralogical and textural properties were observed. In addition, the calcined clay (CC) had higher adsorption capacity for AFB2 (86 vs 99% for CP and CC, respectively) , AFG1 (60 vs 80% for CP and CC, respectively), AFG2 (30 vs 96% for CP and CC, respectively) and ZEN (1 vs 41% for CP and CC, respectively) than the purified clay (CP) at neutral pH.  
In Chapter II, an in vivo toxicokinetic study of AFG1 with or without MMT clay was performed. AFG1 (2 mg/kg BW)  was administered by intravenous injection or orally with or without binder at a dose of 1g/kg BW. The plasma levels of AFG1 were quantified using UHPLC-MS/MS. The presence of possible phase I and phase II metabolites of AFG1 were analyzed using UHPLC-HRMS. A low absolute oral bioavailability of 18.41% was observed for AFG1 in broiler chickens. AFG1 was rapidly absorbed after oral administration and rapidly eliminated after oral as well as IV administration. Furthermore, the efficacy of calcined MMT in binding AFG1 was demonstrated for the first time. Calcination of MMT reduced the oral bioavailability of AFG1 (7.61 ± 4.76%). In addition, no phase I  nor phase II metabolites were detected. These findings confirm that calcination of the purified MMT clay enhanced the adsorption of AFG1 in the gastro-intestinal tract after oral administration, thereby reducing its bioavailability, thus reducing its toxic effects. 
In Chapter III, an in vivo study was performed to evaluate the safety of the mycotoxin binder and possible interactions with nutrients (vitamin A and minerals). The calcined MMT clay was added to broiler chickens feed at  levels of 0.2% and 1%. This experiment demonstrated that the addition of the mycotoxin binder did not alter the absorption of nutrients, indicating safe use.
The second goal of the in vivo experiment was to study the effect of the studied binder on the performance, meat quality and histopathology of broilers. The results demonstrated that the addition of 0.2% of the binder did not alter the growth performance, carcass yield and meat quality of broilers. However, a decrease in abdominal fat was observed in broilers on feed supplemented with calcined MMT. Moreover, nitrogen retention coefficient increased significantly in broilers fed a diet supplemented with 0.2% calcined MMT.
The General Conclusion of this doctoral dissertation was that calcination of Tunisian MMT clay enhanced the adsorption of aflatoxins in the gastro-intestinal tract of broiler chickens. We demonstrated that AFG1 is characterized by low absolute oral bioavailability, as well as the absence of phase I and phase II metabolites. For the possible interaction with nutrients and mycotoxin binders studied in this thesis, no interaction was observed with the inclusion rates of 0.2% and 1% in broiler chickens feed. Moreover, supplementation of broiler chickens feed with 0.2% was safe and did not alter the growth performance and meat quality with a decrease in the carcass adiposity and an improvement of nitrogen retention and nutrient absorption. However, further research is needed to further elucidate the mechanism resulting in these effects.}},
  author       = {{Rejeb, Roua}},
  keywords     = {{clays,montmorillonite,adsorption,mycotoxins,broiler chicken,safety,performance,meat quality,nutrient digestibility}},
  language     = {{eng}},
  pages        = {{181}},
  publisher    = {{Sousse University. Higher Agronomic Institute of Chott-Mariem ; Ghent University. Faculty of Veterinary Medicine}},
  school       = {{Ghent University}},
  title        = {{Characterization and application of a Tunisian clay for the control of mycotoxins in broiler feed}},
  year         = {{2022}},
}