Dose-effect Study of Lipoic Acid Supplementation on Growth Performance in a Weaned Rat Model

The present study investigated the doseeffect relationship of graded levels of lipoic acid supplementation on growth performance and small intestinal development in a weaned rat model. Seventy-two weaned Sprague-Dawley rats, were fed semipurified diets （ n = 12 ）, either unsupplemented （ group I） or supplemented with 12.5,25,125, or 250 mg/kg body weight （ BW ） lipoic acid （ groups HI, IV, V, and VI）, with 200 mg/kg BW aureomycin as the antibiot- ic control （ group II）. The experiment lasted 21 days. Growth performance was not significantly different （P 〉 0.05） between rats under the antibiotic control （group I） and rats fed low levels （12. 5 and 25 mg/kg BW） of lipoic acid （groups III and IV）. In contrast,high level （125 and 250 mg/kg BW） lipoic acid supplementation （groups V and VI） （P 〈 0.05 ） reduced weight gain, feed consumption, and feed efficiency. In addition, high levels （125 and 250 mg/kg BW） of lipoic acid significantly （P 〈 0.05） reduced the villus height/crypt depth ratio, as well as the numbers of lactobacillus, total aerobes, and total anerobes in the gastrointestinal tract compared with the other treatments, which meant that high levels of lipoic acid impaired intestinal morphology and disordered the balance of intestinal microbiology. Furthermore,the results showed that high levels of lipoic acid supplementation （ P 〈 0.05 ） elevated interferon- γ and interleukin-2, but dramatically （ P 〈 0.05 ） depressed interleukin-4 and interleukin-10 compared with the low levels of lipoic acid supplementation and the control group, which indicated that high levels of lipoic acid would induce bias of Th1/Th2 lymphocytes. Taken together, the results indicate that lipoic acid supplementation can＇ t improve growth performance and intestinal development of normal animals, especially,high levels （ ≥ 125 mg/kg BW） of lipoic acid supplementation restrained growth performance and intestinal development, in association with unbalance of certain cytokines.

Comparative efficacy of a phytogenic feed additive and an antibiotic growth promoter on production performance, caecal microbial population and humoral immune response of broiler chickens inoculated with enteric pathogens

The aim of this work was to compare the efficacy of a commercially available phytogenic feed additive(PFA) and an antibiotic growth promoter, which was bacitracin methylene disalicylate(BMD), on performance, nutrient retention, caecal colonization of bacteria and humoral immune responses against Newcastle disease in broiler chickens challenged orally with Salmonella enteritidis and Escherichia coli.One-day-old male Cobb 400 broiler chicks(n = 120) were fed with 1) a negative control(NC) diet, which is the basal diet without any added growth promoter, 2) a positive control(PC) diet, the basal diet supplemented with BMD, 500 mg/kg and 3) a diet supplemented with PFA(150 mg/kg) for 39 days and the birds were inoculated with S. enteritidis and E. coli on d 28. Supplementation of PFA improved body weight, feed conversion ratio, retention of N and crude fiber, increased fecal moisture content and decreased digesta transit time as compared with the NC and PC groups(P <0.01). Both the PC and the PFA was found to be equally effective in controlling the surge in numbers of Salmonella and E. coli following oral inoculation of these bacteria as compared with the NC group(P <0.05) at 24 h past inoculation. Caecal content analysis on d 39 indicated lower numbers of Salmonella, E. coli and Clostridium in the PC and PFA groups as compared with the NC group(P <0.05). The number of Lactobacillus in the PFA group was higher than those in the NC and PC groups(P <0.05). Humoral immune response,measured as hemagglutination inhibition titer against Newcastle disease, was better in the PC and PFA groups compared with the NC group(P <0.05) at d 21 but the difference did not last till d 39. The heterophil to lymphocyte ratio was narrower(P <0.001) and alkaline phosphatase activity was higher(P <0.01) in the PFA group as compared with the NC and PC groups on d 39. It was concluded that the PFA, which is animal, environment and consumer friendly, may be used as an effective replacement for common in-feed antibiotics like BMD to enhance broiler performance especially when the birds are exposed to heavy infections on fields.