Abstract: This study aimed to assess the effects of including the prebiotic Celmanax in both a starter and finishing feed at rates of 2 kg and 1 kg/ton, respectively, as recommended for manufacturing purposes. A total of 240 one-day-old chicks (Aber Acres) were randomly divided into two groups of 120 chicks, including 60 chicks of mixed sexes per replicate (two replicates per group). The experiment was completely randomized with two experimental treatments (one control and one supplement; replicated twice). Chickens were vaccinated for Fowl pox, Tenosynovitis, Marek, Newcastle and Gumboro diseases. All birds received starter feed from one day to three weeks of age and finisher diets from four to six weeks of age. The average weight, feed intake, average daily gain (ADG) and feed conversion ratio (FCR) were determined at weekly intervals for each group. Data were analyzed using a completely randomized design with ANOVA utilizing Minitab software (Minitab 19). Significant differences among treatments were identified using Duncan’s new multiple range test. Average weights for Celmanax added feed were higher at week one (p<0.05), whereas control diets showed higher weights at weeks 4, 5 and 6. The average daily gain was greater (p<0.05) for control diets at weeks 3, 4 and 5. There were no significant differences (p>0.05) in the feed conversion ratio (range 0.68-0.95 kg) across treatments for the 6 week study period. There were no differences (p>0.05) between the Celmanax and control diet regarding feed intakes and FCR during the overall six week period, while mortality was higher (p<0.05) in the Celmanax group. Present study did not identify the expected benefits in growth rates, feed intake rates and FCR, or reduced mortality, as expected based on other studies. This was likely a consequence of the presence of unconfirmed mycotoxins in the feeds and poor quality egg sources.