The mothering ability of a sow largely depends on the shape and function of the mammary gland. The aim of this study was to identify QTL for the heritable inverted teat defect, a condition characterized by disturbed development of functional teats. A QTL analysis was conducted in a porcine experimental population based on Duroc and Berlin Miniature pigs (DUMI). The significant QTL were confirmed by linkage analysis in commercial pigs according to the affected sib pair design and refined by family-based association test (FBAT). Nonparametric linkage (NPL) analysis revealed five significant and seven suggestive QTL for the inverted teat defect in the porcine experimental population. In commercial dam lines five significant NPL values were detected. QTL regions in overlapping marker intervals or close proximity in both populations were found on SSC3, SSC4, SSC6, and SSC11. SSC6 revealed QTL in both populations at different positions, indicating the segregation of at least two QTL. The results confirm the previously proposed polygenic inheritance of the inverted teat defect and, for the first time, point to genomic regions harboring relevant genes. The investigation revealed variation of the importance of QTL in the various populations due to either differences in allele frequencies and statistical power or differences in the genetic background that modulates the impact of the liability loci on the expression of the disease. The QTL study enabled us to name a number of plausible positional candidate genes. The correspondence of QTL regions for the inverted teat defect and previously mapped QTL for teat number are in line with the etiologic relationship of these traits.

Parathyroid hormone-like hormone gene (PTHLH) and its receptor, parathyroid hormone/ parathyroid hormone-like hormone receptor 1 (PTHR1), play a role in epithelial mesenchymal interactions during growth and differentiation of different tissues and anatomic structures, including teats. Therefore, PTHLH and PTHR1 were evaluated as functional candidate genes for their effects on number and shape of teats in pigs. In particular, focus was on the occurrence and number of inverted teats, the most frequent and economically relevant teat developmental defect in pigs. For this purpose, association and linkage of the PTHLH gene and the PTHR1 gene with inverted teat defect and the total number of teats and inverted teats were studied in an experimental Duroc and Berlin Miniature pig (DUMI) population. Polymorphism C1819T of PTHR1 was significantly associated with inverted teat phenotype (p = 0.014), total number of teats (p = 0.047) and was close to significance with the number of inverted teats (p = 0.078). Polymorphism C375T of PTHLH was close to significance with the inverted teat phenotype (p = 0.122) and showed no significant association with the total number of teats (p = 0.621) and the number of inverted teats (p = 0.256) in the DUMI population. Association analyses were also performed for combined effects of PTHLH and PTHR1 in order to address potential interaction, however, revealed no indication of effects of interaction. The function, position and the association shown here promote PTHR1 as a candidate gene for number of teats and in particular for affection by and number of inverted teats.

In this study 8 genes of growth factors and their receptors were investigated that are known to play a significant role in signaling pathways involved in the ontogenetic, but also tumorigenic, development of breast and mammary glands. Differential expression of fibroblast growth factor receptor 2 (FGFR2), GH receptor (GHR), hepatocyte growth factor (HGF), hepatocyte growth factor receptor (HGFR), platelet-derived growth factor alpha (PDGFA), platelet-derived growth factor receptor alpha (PDGFRA), platelet-derived growth factor beta (PDGFB), and vascular endothelial growth factor (VEGF) was analyzed in mesenchymal and epithelial teat tissue of peripubertal pigs affected and nonaffected by the inverted teat defect. Comparisons were made at the level where pigs were affected between samples derived from nonaffected animals and affected animals, including specimens of normal and inverted teats. In addition, comparisons were made at the level of the teat phenotype with normal teats of nonaffected animals vs. either the normal or the inverted teat of affected animals. All genes tested, except HGFR, showed significant differential expression at P < 0.05 in the mesenchymal or the epithelial teat tissue or both. In general, we observed more pronounced differences when comparing samples obtained from inverted tissues vs. samples from normal ones. Therefore, results of our study suggest that gene expression of the growth factors and their receptors associates directly with the teat phenotype rather than with the affection status of the investigated animals, suggesting that local processes and tissue-specific compensation by means of differential expression of growth factors and their receptors are responsible for the development of impaired teat phenotypes.

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Abstract. The parathyroid hormone/parathyroid hormone like hormone type I receptor (PTHR1) belongs to the family of G protein-coupled receptors for peptide hormones, including parathyroid hormone (PTH) and parathyroid hormone like hormone (PTHLH), which participate in epithelial-mesenchymal interactions during the formation and differentiation of epithelial organs (FOLEY et al., 2001; CHOMDEJ et al., 2004). The function of PTHR1 and its ligands suggest its candidacy for traits related to the development of bones and joints but also of mammary gland. The porcine gene was screened for SNPs and assigned to SSC13.