Size of supernumerary teats in sheep correlates with complexity of the anatomy and microenvironment

Abstract

Supernumerary nipples or teats (polythelia) are congenital accessory structures that may develop at any location along the milk line and have been implicated in the pathogenesis of mastitis. We describe the anatomy and histology of 27 spontaneously occurring supernumerary teats from 16 sheep, delineating two groups of teats – simple and anatomically complex – according to the complexity of the anatomy and microenvironment. Anatomically complex supernumerary teats exhibited significantly increased length and barrel diameter compared with simple supernumerary teats. A teat canal and/or teat cistern was present in anatomically complex teats, with smooth muscle fibres forming a variably well‐organised encircling teat sphincter. Complex supernumerary teats also exhibited immune cell infiltrates similar to those of normal teats, including lymphoid follicle‐like structures at the folds of the teat cistern–teat canal junction, and macrophages that infiltrated the peri‐cisternal glandular tissue. One complex supernumerary teat exhibited teat end hyperkeratosis. These anatomical and histological features allow inference that supernumerary teats may be susceptible to bacterial ingress through the teat canal and we hypothesise that this may be more likely in those teats with less well‐organised encircling smooth muscle. The teat cistern of anatomically complex teats may also constitute a focus of milk accumulation and thus a possible nidus for bacterial infection, potentially predisposing to mastitis. We suggest that size of the supernumerary teat, and relationship to the main teats, particularly in the case of ‘cluster teats’, should be considerations if surgical removal is contemplated.

Developing ovine mammary terminal duct lobular units have a dynamic mucosal and stromal immune microenvironment

“…The macrophage marker ionised calcium binding adaptor molecule 1 (IBA1) is expressed by macrophages and microglia and is involved in macrophage membrane ruffling 40 . We have previously utilised this marker to detect ovine mammary macrophages 41 . In the present study, using IBA1 IHC to identify macrophages, we noted distinct periodicity of intraepithelial macrophages both within ducts and ductules (Fig.…”

Development and Pathology of the Equine Mammary Gland

“…As already described, each equine teat exhibits two MPSU. Similar to ruminants [36], the equine mammary teat canal is surrounded by sparsely cellular connective tissue and smooth muscle fibres (Fig. 1).…”

Developing mammary terminal duct lobular units have a dynamic mucosal and stromal immune microenvironment

“…The macrophage marker ionized calcium binding adaptor molecule 1 (IBA1) is expressed by macrophages and microglia and is involved in macrophage membrane ruffling (Ohsawa et al, 2000). We have previously utilized this marker to detect ovine mammary macrophages (Hardwick et al, 2020). In the present study, using IBA1 IHC to identify macrophages, we noted distinct periodicity of intraepithelial macrophages both with ducts and ductules (Fig.…”