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Matrix metalloproteinase 9 (MMP9) plays critical roles in multiple biological processes, such as reproduction, cell proliferation and differentiation, and host defenses. The aim of this study was to evaluate whether MMP9 is a candidate gene for resistance to diarrhea in piglets. In this study, quantitative real-time PCR was used to analyze the expression of MMP9 mRNA in different tissues of specific pathogen-free piglets. MMP9 was expressed in all the tissues (heart, liver, spleen, lung, kidney, stomach, duodenum, jejunum, ileum, and colon) analyzed. An association analysis between MMP9 polymorphisms and piglet diarrhea score and performance traits were performed in Min (Chinese indigenous breed) and Landrace populations. In the statistical analysis, at the g.48178429 GA locus, AA piglets had a lower diarrhea score than that of GA in the Min population (P .05), whereas GG had higher day-35 body weight and average daily gain (ADG) than AA in the Landrace breed (P .05). At the rs336583561 locus, Min piglets with the GG genotype have a lower diarrhea score than AG piglets (P .05). At g.48184777CT, CC animals have higher body weight than TC Landrace piglets (P .05 or P .01). A 5' flanking deletion assay indicated that g.48178429 GA was not located in the MMP9 promoter region. Our results suggest that the A allele at the g.48178429 GA locus and the G allele at rs336583561 are resistance alleles in Min pigs. Before these markers are used in pig breeding programs, more studies in larger populations are needed.

The objective of this study was to evaluate the association between the cytotoxic T-lymphocyte-associated antigen 4 (CTLA4) gene and piglet diarrhea. In this study, the mRNA expression of the CTLA4 gene increased significantly in IPEC-J2 cells after Escherichia coli K88 infection. Single nucleotide polymorphisms (SNPs) located in the 5' flanking region (SNPs g.107281989CT) and 3'-untranslated region (3'-UTR; SNPs g.107288753CA) were identified, and they were in linkage disequilibrium in both Min pigs and the Landrace population. Association analysis showed that Landrace piglets with a TT or AA genotype had a lower diarrhea index, and AA animals had higher average daily gain when compared to CC pigs, respectively (p 0.05). However, the relationship between SNPs and diarrhea and performance traits in the Min population was not significant. Haplotype analysis indicated that the TC haplotype had the lowest diarrhea index. The 5' flanking deletion assay suggested that SNP g.107281989CT was a molecular marker instead of the functional marker. This research demonstrated that genetic variances in the CTLA4 gene had significant effects on Landrace piglet diarrhea resistance.