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Abstract: Inactivated mycobacterium phlei (M. phlei) is well known for its immune‐stimulatory functions in humans and livestock, but less information is available about the influence on meat quality of pigs when used as a feed additive. This study was designed to evaluate the effects of inactivated M. phlei on growth performance as well as meat quality of fattening pigs. A total of 240 cross‐bred pigs ([Landrace × Yorkshire] × Duroc) with initial body weight of 80.14 ± 0.29 kg were randomly allocated to five treatments, each of which consisted of eight replicates with 6six pigs per replicate. The basal diet supplemented with five levels of inactivated M. phlei preparations (0, 3.5 × 109 [0.1% w/w], 7 × 109 [0.2%], 1.4 × 1010 [0.4%] or 2.1 × 1010 [0.6%] colony‐forming units/kg) was respectively fed to the control group and four treatment groups for 30 days. Adding 0.4% of inactivated M. phlei to diet increased the average daily feed intake and average daily gain of pigs. Importantly, intramuscular fat percentage in the Longissimus dorsi (LD) was increased by feeding diet containing 0.2%, 0.4% and 0.6% of inactivated M. phlei, despite the pH value, drip loss, cooking loss and filter paper fluid uptake not being influenced. Analysis of the fatty acid components showed that some saturated fatty acids were decreased in LD after feeding inactivated M. phlei, but some monounsaturated fat acids (MUFAs) and polyunsaturated fatty acids were increased (PUFAs), which induced the total contents of MUFAs and PUFAs were improved. RT‐PCR assay revealed that feeding inactivated M. phlei up‐regulated genes implicated in fat metabolism in muscle, including ELOVL6, FASN, SCD1 and H‐FABP. This study revealed that feeding inactivated M. phlei not only increased growth performance of fattening pigs, but also improved the meat quality by increasing intramuscular fat content, thus inactivated M. phlei probably has high utilization value in modern pig production. [ABSTRACT FROM AUTHOR]

The contradiction between high susceptibility of early weaned piglets to enteric pathogens and rigid restriction of antibiotic use in the diet is still prominent in the livestock production industry. To address this issue, the study was designed to replace dietary antibiotics partly or completely by an immunostimulant, namely heat-killedMycobacterium phlei(M. phlei). Piglets (n = 192) were randomly assigned to one of the four groups: (1) basal diet (Group A), (2) basal diet + a mixture of antibiotics (80 mg/kg diet, Group B), (3) basal diet + a mixture of antibiotics (same as in Group B, but 40 mg/kg diet) + heat-killedM. phlei(1.5 g/kg diet) (Group C) and (4) basal diet + heat-killedM. phlei(3 g/kg diet) (Group D). All piglets received the respective diets from days 21 to 51 of age and were weaned at the age of 28 d. Compared with the Control (Group A), in all other groups the average daily gain, average daily feed intake, small intestinal villus height:crypt depth ratio and protein levels of occludin and ZO-1 in the jejunal mucosa were increased. A decreased incidence of diarrhoea in conjunction with an increased sIgA concentration in the intestinal mucosa and serum IL-12 and IFN-γ concentrations was found in groups supplemented with heat-killedM. phlei(Groups C and D), but not in Group B. Groups C and D also showed decreased IL-2 concentrations in the intestinal mucosa with lower TLR4 and phosphor-IκB protein levels. The antioxidant capacity was reinforced in Groups C and D, as evidenced by the reduction in malondialdehyde and enhanced activities of antioxidant enzymes in serum. These data indicate that heat-killedM. phleiis a promising alternative to antibiotic use for early weaned piglets via induction of protective immune responses. [ABSTRACT FROM PUBLISHER]