Bopape, Malebogo Audrey2025-10-302024Bopape, Malebogo Audrey. (2024). Effects of dietary supplementation with β-sitosterol on Cobb 500 broiler chicken productivity, health and product quality [PhD thesis, University of the Witwatersrand, Johannesburg]. WIReDSpace. https://hdl.handle.net/10539/47279https://hdl.handle.net/10539/47279A research report submitted in fulfillment of the requirements for the Doctor of Philosophy, in the Faculty of Health Sciences, School of Physiology, University of the Witwatersrand, Johannesburg, 2024Antibiotic use as growth promoters in chicken feeds results in antibiotic resistance and environmental pollution. To mitigate these challenges alternatives natural growth promoters are required. Beta-sitosterol is one of several phytosterols with chemical structures similar to that of cholesterol. β-sitosterol has antimicrobial, antioxidant, anti-inflammatory and hypocholesterolaemic activities, thus might replace synthetic antibiotics as a feed supplement in chicken feeds. The current study evaluated β-sitosterol’s potential to replace oxytetracycline in Cobb 500 broiler chicken feeds by determining its effects on growth performance, meat yield and quality and bird health. β-sitosterol replaced oxytetracycline at 0 (control: 50 mg/kg oxytetracycline), 500, 1000 and 1500 mg/kg feed for diet 1 to 4, respectively with doses similar in starter, grower, and finisher diets. Chickens were fed from day 1 to 42 days of age. Body mass and feed intake were measured. Body mass gain, average daily gain and feed conversion ratio were computed. Terminally, broiler chickens were fasted, weighed, humanely slaughtered and dressed. The carcass yield, viscera morphometry and plasma surrogate markers of health were also determined. Meat pH, colour, thawing and cooking loss (TL; CL), water holding capacity (WHC), tenderness and myofibrillar fragmentation length (MFL) and nutrient content were determined. Femora and tibiae mass, length, breaking strength and liver fat content and histology were determined. Dietary β- sitosterol had similar (P > 0.05) effects as oxytetracycline on the chickens’ growth performance and feed intake utilization efficiency, gastrointestinal tract (GIT) and GIT accessory viscera macromorphometry, meat yield, meat colour, pH, TL, CL, WHC, tenderness and MFL. However, breast meat crude protein content of chicken fed diet 4 was higher (P < 0.0001) compared to that of counterparts fed diets 2 and 3. Breast meat fat content of chicken fed diet 2 and diet 4 was higher (P < 0.0001) compared to that of counterparts fed diets 1 and 3. Dietary β-sitosterol had similar (P > 0.05) broiler chickens’ breast meat total saturated fatty acids (TSFAs), monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs), palmitic, oleic and linoleic content as oxytetracycline. Dietary treatments had no effect on chickens’ tibiae masses and breaking strength (P > 0.05) albeit tibiae from chickens fed diet 4 were shorter (P < 0.01) than those of counterparts fed diet 2. Dietary β-sitosterol at 1000 and 1500 mg/kg feed increased (P < 0.05) liver lipid content but had no effect on hepatic microarchitecture. However, at 1500 mg/kg feed it caused micro- and macro hepatic steatosis and lobular inflammation and higher (P < 0.05) non-alcoholic fatty liver disease activity scores (NAS). Compared to control, dietary β- vii sitosterol decreased (P < 0.0001) the chickens’ malondialdehyde (MDA) concentration but increased superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) activities and glutathione S-transferase (GST) and glutathione (GSH) concentration (P < 0.05). Diet 4 increased (P < 0.01) plasma AST and GGT activities compared to diet 1 (control). At 1000 and 1500 mg/kg feed it increased plasma cholesterol concentration compared to control and β-sitosterol at 500 mg/kg feed. β-sitosterol can replace oxytetracycline as growth promoter in Cobb 500 broiler chicken diets without negatively affecting growth performance, meat yield and quality and potentially mitigates oxidative stress by upregulating systemic antioxidant enzymes activities. However, at 1500 mg/kg feed, it can increase the risk of fatty liver disease development and hypercholesterolaemia.en© 2024 University of the Witwatersrand, Johannesburg. All rights reserved. The copyright in this work vests in the University of the Witwatersrand, Johannesburg. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of University of the Witwatersrand, Johannesburg.UCTDdietary supplementationβ-sitosterolCobb 500 broiler chicken productivityThesisUniversity of the Witwatersrand, JohannesburgSDG-3: Good health and well-being