Effects of Heat-Killed Lactobacillus plantarum L-137 Supplementation on Growth Performance, Blood Profiles, Intestinal Morphology, and Immune Gene Expression in Pigs

SIMPLE SUMMARY: Antibiotic growth promoters have long been used in pig diets to maintain gut health and improve growth performance. However, the overuse of antibiotics has led to the emergence of antibiotic-resistance microbes, an imbalance of the healthy intestinal microflora, and antibiotic residues. As a result, probiotic bacteria have been used as an alternative to antibiotics in pig production. Nevertheless, in-feed probiotics may be inconsistent due to differences in preparation methods, feed storage, and ability to survive through the gastrointestinal tract. Heat-killed Lactobacillus plantarum L-137 (HK L-137), also known as a paraprobiotic, has been shown to have beneficial effects on the immune response and has no limitations. Our study indicates that supplementing HK L-137 in pig diets can improve production performance and promote immune function. ABSTRACT: In the present study, the effects of dietary heat-killed Lactobacillus plantarum L-137 (HK L-137) on the productive performance, intestinal morphology, and cytokine gene expression of suckling-to-fattening pigs were investigated. A total of 100 suckling pigs [(Large White × Landrace) × Duroc; 4.5 ± 0.54 kg initial body weight (BW)] were used and assigned to each of the four dietary treatments as follows: (1) a control diet with antibiotics as a growth promoter (AGP) from the suckling phase to the grower phase and no supplement in the finisher phases; (2) a control diet without antibiotics as a growth promoter (NAGP); (3) a control diet with HK L-137 at 20 mg/kg from the suckling phase to the starter phase and no supplement from the grower phase to the finisher phases (HKL1); and (4) a control diet with HK L-137 at 20 mg/kg from the suckling phase to the weaner phase, at 4 mg/kg from the starter phase to the finisher 1 phase, and no supplement in the finisher 2 phase (HKL2). During the weaner–starter period, the pigs fed on the AGP and HKL2 diets showed significantly higher weight gain and average daily gain (ADG) than those in the NAGP group (p < 0.05). The pigs in the AGP, HKL1, and HKL2 groups showed greater ADG than those in the NAGP groups (p < 0.05) throughout the grower–finisher period. The suckling pigs in the HKL1 and HKL2 groups showed a higher platelet count (484,500 and 575,750) than in the others (p < 0.05); however, there were no significant differences in the other hematological parameters among the treatment groups. The relative mRNA expression level of IFN- ß of the suckling and starter pigs were significantly higher in the HKL1 and HKL2 groups than in the others (p < 0.05), while the IFN-γ showed the highest level in the HKL2 suckling pigs (p < 0.05). These results demonstrate that a HK L-137 supplementation could stimulate the immune response in suckling and starter pigs and promote the growth performance in finishing pigs.