Potency of New Additives in Controlling Coccidiosis and Necrotic Enteritis in Broiler Chickens, Under In Vitro and In Vivo Conditions

Abstract

<p>Necrotic enteritis (NE) is a detrimental poultry disease that drastically damages the intestinal microstructure and can result in decreased production, increased mortality rates, animal welfare issues, and higher veterinary costs. The well-known cause of NE is <i>Clostridium perfringens</i> residing in the intestines. The presence of predisposing factors, such as coccidiosis, can lead to higher abundance of <i>C. perfringens</i> (more than 10⁷ cfu) and onset of NE. The global annual cost of NE to the poultry industry has been estimated to be as high as US$6 billion. The use of antibiotics in poultry feed was once a common strategy to control NE, but this practice has been banned in the European Union and is being phased out globally due to the emergence of antibiotic-resistant bacteria, which poses a risk to human health. As a result, alternatives to antibiotics have been sought and used in the poultry industry to maintain health and production of poultry when antibiotics are not used. These include pro- and prebiotics, organic acids, plant extracts, and enzymes. However, the effectiveness and mode of actions of the additives are still under great debate and thus research is needed. In this thesis, I examined the effects of different additives against NE and coccidiosis in broiler chickens to investigate their roles in the health and performance of the birds.</p> <p>• Chapter 1: presented a short introduction to describe NE, reviewed the current strategies for controlling NE, and introduced the main objectives of the experimental chapters.</p> <p>• Chapter 2: reviewed predisposing factors of NE and measures and materials for controlling NE to provide a concise overview of current remedies for the disease.</p> <p>• Chapter 3: describes the outcome of an <i>in vitro</i> experiment that examined the effects of a processed sugarcane extract (Polygain™) on the livability of different <i>Eimeria</i> spp. sporozoites, as the main predisposing factor for NE. Treatments were: 1) without additives (no-treatment control); 2) with ethanol; 3) with salinomycin; 4) with Polygain™. Results showed that Polygain™ decreased (P<0.001) the counts of <i>E. maxima</i>, <i>E. acervulina</i>, <i>E. bruneti</i>, and <i>E. mitis</i> sporozoites compared to the no-treatment control and to a level similar to salinomycin (P>0.05). The study indicated that Polygain™ can be used as a candidate to mitigate poultry coccidiosis.</p> <p>• Chapter 4: presents the results of a study that evaluated the effects of two doses of xylanase and β-glucanase on broilers' performance, gut health, and welfare under the <i>Eimeria</i> challenge as a predisposing factor for NE. Treatments were: 1) non-challenged control (NC, wheat-SBM based diet including rye and barley); 2) NC + <i>Eimeria</i> challenge (CC: challenged control); 3) CC + recommended level of xylanase and β-glucanase (XG, 100 g/t feed, Natugrain® TS, BASF); 4) CC + double recommended level of XG (2XG, 200 g/t feed). Results revealed that the addition of xylanase and β-glucanase improved weight gain and FCR, decreased litter moisture and footpad dermatitis, reestablished the population of <i>Lactobacillus</i> in the cecum of challenged birds, and tended to increase the expression of junctional adhesion molecule 2 (JAM2) in broilers under <i>Eimeria</i> challenge. The results also showed that the single recommended dose of combined enzymes should be enough for the birds under the conditions of the current study. Overall, the combination of xylanase and β-glucanase had a positive impact on the performance and gut health of broilers under the <i>Eimeria</i> challenge.</p> <p>• Chapter 5: examined the impact of individual buffered formic acid (Amasil® NA) and monoglycerides of short- and medium-chain fatty acids (Balangut® LS P) and their combinations on the performance and gut health of broiler chickens under NE. Treatments were: T1) non-challenged control; T2) NE challenged control; T3) Amasil® NA (challenge plus Amasil® NA, 0.3% throughout all phases); T4) Balangut® LS P (challenge plus Balangut® LS P, 0.5%, 0.3%, and 0.2% in the starter, grower and finisher phases respectively; T5) Combined (challenge plus combination of T3 and T4); T6) Antibiotic (challenge plus Zn bacitracin, 0.05 % throughout all phases). The results showed that compared to non-challenged birds, the use of Balangut® LS P significantly improved (P<0.05) FCR of challenged birds, and its performance was comparable to that of antibiotics. The use of Amasil® NA helped to shift the bacterial counts of <i>Bifidobacteria</i>, Enterobacteriaceae, and <i>Lactobacillus</i> towards non-challenged control (P>0.05). Balangut® LS P showed an intermediate (P>0.05) expression pattern of IL21R, ZAP70, and DUSP4 towards non-challenged and antibiotic groups. The results suggested that a combination of Balangut® LS P and Amasil® NA is promising in improving chickens' performance and gut health, particularly under challenging conditions such as NE infections.</p> <p>• Chapter 6: presents the results of a study that evaluated the effects of spray-dried porcine plasma (SDP) supplementation during the starter phase (days 0 to 10) on broilers' performance and gut health under the NE challenge. Treatments were arranged in a 2 (NE challenge: no, yes) × 2 (SDP: 0, 2%) factorial design. Results showed that adding SDP reduced the FCR during the pre-challenge phase (days 0 to 8) and the whole experimental period (days 0 to 29) (P<0.01). In addition, a decrease in the concentration of FITC-d and an increase in the relative weight of bursa (g/kg live BW) were observed in the challenged birds supplemented with SDP (P<0.05). Supplementation with SDP also led to a decrease in the concentration of interleukin-6 (P<0.05) and α-1 acid glycoprotein (P=0.051) in serum samples. Overall, the study demonstrated that the addition of SDP during the starter phase can improve feed efficiency and gut integrity in broilers challenged with NE, possibly by stimulating the immune response.</p>