The Efficacy of Synbiotic Application in Broiler Chicken Diets, Alone or in Combination with Antibiotic Growth Promoters on Zootechnical Parameters

In recent years, probiotics and synbiotics have gained considerable interest in poultry feeding as an alternative to antibiotics due to antibiotic resistance concerns. The objective of this dual study was to evaluate the efficacy of synbiotic supplementation alone or in combination with different Antibiotic Growth Promoters (AGPs), compared to the untreated control group of broiler chickens production performance. In the first experiment, a total of 1260 one-day-old male Ross 308 broiler chickens were randomly assigned to 7 diet treatments, with 6 replicates per diet treatment and 30 birds per replicate over a 42-day period. The diet treatments included a control diet based on corn-soybean without additives (T1), and the diet treatment with bacitracin (BMD 100 ppm, T2), colistin (10 ppm, T3), synbiotic (PoultryStar me, 0.5 kg/t, T4), a combination of synbiotic (0.5 kg/t) and bacitracin (60 ppm, T5), synbiotic (0.5 kg/t) and colistin (5 ppm, T6), synbiotic (0.5 kg/t), bacitracin (60 ppm), and colistin (5 ppm, T7). During the critical period of rearing from hatch to day 10, the synbiotic supplementation resulted in a significantly higher body weight gain than its combination with bacitracin. No other dietary treatment showed a remarkable improvement in the body weight gain, feed intake, or feed conversion ratio, compared to the only synbiotic application (T4) during the entire trial period. The tendency towards an improved feed conversion ratio was observed during the use of symbiotic (T4, 1.87), compared to the control group (T1, 1.93) during the entire trial period. Compared with the control group (T1, 2.78%), broiler mortality was also lower in the synbiotic group (T4, 1.11%). In the second experiment, a total of 1500 one-day-old male Ross 308 broiler chickens were randomly assigned to 4 diet treatments; with 15 replicates per diet treatment, and 25 birds per replicate over a 42-day period. The dietary treatments included a control group diet based on corn-soybean without additives (T1), and the treatment diets with bacitracin (BMD 1000 ppm, T2), synbiotic (PoultryStar me, 0.5 kg/t, T3), and a combination of synbiotic (0.5 kg/t) plus bacitracin (BMD 1000 ppm T4). Birds fed antibiotic or synbiotic alone or in a combination had numerically a higher body weight and an average daily gain than the control group. There was a tendency of improvement in the feed conversion ratio during the age of 1-24 days, and throughout the experimental period. The evaluated synbiotic could serve as an effective alternative to AGPs, such as bacitracin and colistin in broiler chicken diets, especially during the first crucial period. The synbiotic can serve this purpose without combining it with AGPs, such as colistin or bacitracin.