Effects of probiotic and antibiotic on performance of broilers

Three experiments were conducted to determine the effects of a probiotic co mbination (L. plantarum, L. delbrueckii subsp. bulgaricus, L. acidophilus, L. rhamnosus, Bifidobacterium bifidum, Streptococcus salivarius subsp. ther mophilus, Enterococcus faecium, Aspergillus oryza and Candida pintolopesii cultures, 3 x 10(11) CFU/kg, starter; 2 x 10(11) CFU/kg, grower) and/or ant ibiotic (zinc bacitracin, 75 ppm) on the body weight gain and feed efficien cy of broiler-type chicks. In Experiment 1, average weight gain was increased by feeding the diet cont aining antibiotic during the first 3-wk period as compared to the control, probiotic and combination of probiotic and antibiotic: (p < 0.05). When add ed to the diet, probiotic, antibiotic and combination of probiotic and anti biotic decreased live weights of birds at the end of the experiment, and re duced feed intake (3511.0, 2990.9, 3153.1 and 3007.9 gram, respectively) an d feed/gain ratio (1.90, 1.86, 1.89 and 1.86, respectively). In Experiment 2, average weight gain and feed/gain ratio was depressed by f eeding the diet containing combination of probiotic and antibiotic as compa red to the control, probiotic and antibiotic during the first 3-wk period ( p < 0.05). Otherwise, adding probiotic to the starter diet (3 x 10(11) CFU/ kg) increased feed intake. At the end of the experiment, single administrat ion of probiotic supplement resulted in somewhat higher responses than in c ontrol, zinc bacitracin and combination with zinc bacitracin. Combined admi nistration of probiotic and antibiotic significantly reduced the growth rat e of birds (p < 0.05), as well as feed conversion in comparison to the cont rol and probiotic. In Experiment 3, mean weights of broilers which were fed probiotic suppleme nted diet were the lowest at 3 and 5 wk among treatments. Feed intake was d ecreased by probiotic alone at 0-21 days. Feed efficiency ratio was numeric ally decreased with the addition of antibiotic and combination probiotic an d antibiotic supplemented to the diet at starter period. At the end of the experiment, the addition of either probiotic or antibiotic to the diet resu lted in chicks with numerically decreased body weights over chicks fed the control diet. When probiotic and zinc bacitracin were added, in combination to the diet, the body weights: of the broilers were statistically lower th an the control group, associated with a numerical decrease in feed intake. The results of the study indicate that addition of only probiotic and antib iotic to the diet did not influence broiler performance kept under good hyg ienic conditions.