| In this paper, four kinds of substitutes for antibiotics, that is Oregano extract, Tea tree oil extract, tnymol and Carvacrol preparation, Cinnamaldehyde capsaicin preparation were used to research their inhibitory effects on common pathogenic bacteria and the effects on growth performance, organ index, digestive system and immune system of chicken. Also the mechanisms were explored to provide some scientific theoretical basis for the research and application of antibiotics substitutes.The inhibitory effect of different antibiotics substitutes on common pathogenic bacteria was studied in experiment one. The inhibitory effects of Oregano extract, Tea tree oil extract, tnymol Carvacrol preparation and Cinnamaldehyde capsaicin preparation on Escherichia coli, Staphylococcus aureus, Salmonella, Pasteurella, Aeromonas hydrophila were evaluated by the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) compared with Bacitracin Zinc. The results show that a certain concentration of antibiotic alternatives could inhibit the growth of some common pathogens, and the inhibitory effects of thymol and carvacrol preparation on Staphylococcus aureus and Salmonella are higher than Bacitracin Zinc and other antibiotics alternatives, while Race cadherin has the better suppressing effects on Pasteurella, Aeromonas hydrophila Aeromonas.In the second experiment, the effect of different antibiotic substitutes on growth performance and organ index was studied.15001-day-old broilers (AA♂×Minnan yellow chicken♀) were divided into5groups, each group included6repeats and50broilers in each repeat. Basic diets adding Bacitracin Zinc was treated as control group, while the experimental groups were added with Oregano extract(Ⅰ), Tea tree oil extract(Ⅱ), tnymol and Carvacrol preparation(Ⅲ), Cinnamaldehyde capsaicin preparation(IV). This experiment was divided into earlier stage (1-21days old) and later stage (21-42days old) and no other antibiotics were added in the whole experimental stage except coccidiostat. In the earlier stage, it was found that there was no significant difference in feed intake and feed to gain ratio(F/G)(P>0.05), while F/G tend to decrease compared with control groups, and average daily gain of group II was significantly higher than the group Ⅳ(P<0.05) and other groups(P>0.05), and the survival rate of group I, III, IV were higher than group II or control group(P>0.05). Meanwhile, cardiac index, liver index and pancreas index of21-old-day broilers had no significant difference; In the late stage, the average daily feed intake, daily gain, F/G also have no different significance(P>0.05); Cardiac index and pancreas index of42-old-day broilers showed no significant difference(P>0.05), while liver index of broilers in experimental group I was significantly higher than control group(P<0.05) and other groups(P>0.05). These results indicated that antibiotic substitutes have no negative effects on broilers’growth and organic indexes, and adding antibiotic substitutes could decrease F/G in the earlier stage.In the third experiment, the influence of substitutes for antibiotics on protease, amylase and lipase activities in pancrease and duodenal contents, the morphology of jejunum and ileum villus, as well as cecal microbial community structure. The results showed that duodenal trypsin activity in group II is significantly higher than those in other groups(P<0.05), amylase and lipase activities have no significant changes among experimental groups; At42days, duodenal amylase activities in group III significantly above control group(P<0.05), and antibiotic alternatives have no effects on trypsin and lipase activities. At21days old, ileum villi length and crypt depth in group I were significantly higher than those in group IV and control group(P<0.01), as well as group III was significantly higher than group IV (P<0.05) and control group (P<0.01), but V/C of group III was lower than other groups.At21days, jejunum villus height and thickness of bowel wall had no significant difference (P>0.05); Crypt depth of group IV was less than that of control group (P>0.05) and significantly less than that in the other experimental groups (P<0.05), while V/C was greater than that of control group (P<0.05) and significantly greater than that in the other trial groups (P<0.01). At42days, ileal crypt depth in each experimental group were less than that of control group, V/C values were higher than that of control group (P>0.05), and villus height of group I was higher than that of control group (P>0.05), significantly higher than that of group IV, while intestinal wall thickness of group II was significantly less than that of control group and other test groups (P<0.05); In terms of jejunum villus height, group I was significantly higher than control group and other experimental groups (P<0.01), and V/C in group I was significantly greater than that in group IV (P<0.01), however there was no significant difference between the groups of intestinal wall thickness. The number of cecal Escherichia coli in every experimental group was lower than that in control group (P>0.05) at both21days old and42days old, while caecal lactic acid bacteria of group Ⅱ are higher than that of control group (P>0.05), and significantly greater than that of group I and group IV (P<0.05) at21days old; At42days, caecal lactic acid bacteria number in every experimental group was higher than that in control group (P>0.05). These results indicate that antibiotic alternatives could guarantee the growth and health of broilers to a certain extent by enhancing the digestive enzyme activities, promoting the development of small intestine villi of broilers, and effectively inhibiting the proliferation of harmful bacteria. In the fourth experiment, the influence of substitutes for antibiotics on the immune organ index, serum immunoglobulin, superoxide dismutase (SOD), alkaline phosphatase (AKP), lysozyme and antibody titer of Newcastle disease (ND-HI) levels. The results are as follows: thymus, bursa of Fabricius, spleen index among all groups did not differ significantly (P>0.05), also spleen, thymus index at42days (P>0.05). While bursa of Fabricius index in group I were higher than that in control group(P>0.05) and other groups(II and III, P<0.05; IV, P<0.01);At21days and42days, serum IgA, IgM, IgG, SOD, lysozyme in each experimental group had no significant difference (P>0.05) compared with the control group. AKP in group IV was significantly higher than that in control group and group I, II, III (P<0.01), also AKP in group III was significantly higher than that of group II (P<0.05) and group I or control group (P<0.01);At42days, AKP in group IV was significantly higher than that in other treatments (P<0.01), and group Ⅲ was significantly higher than group I (P<0.05) and control group or group II (P<0.01). Levels of ND-HI of every experimental group were higher than that of control group at17days,21days,24days,42days old, and ND-HI of group I was higher than that of control group and group IV (P<0.05) at21days. We could conclude that antibiotic alternatives would enhance immunity function of broilers. |
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