Gastrointestinal transport of calcium and phosphate in lactating goats

Abstract

Previous studies gave evidence for the assumption that in contrast to sheep, dairy goats can adapt to lactation-induced challenges of calcium (Ca) homeostasis by effective adaptation of gastrointestinal Ca absorption. Ca and phosphate (Pi) homeostasis are known to be closely related challenged during lactation. However, for both, Ca and Pi homeostasis, the underlying molecular mechanisms and their regulation during lactation in goats have only marginally been investigated so far. Therefore, the present study aimed to investigate the impact of lactation on gastrointestinal Ca and Pi absorption in dairy goats on a functional level using the Ussing chamber technique to determine macromineral fluxes across gastrointestinal epithelia, and on a structural level by analyzing gastrointestinal RNA and protein expression of key genes involved in transcellular Ca and Pi transport. Besides slightly increased functional Ca absorption and elevated expression of transient receptor potential vanilloid channel type 6, calbindin D9K and plasma membrane Ca2+-ATPase type 1 in jejunum, an upregulation of Ca absorption in lactating goats also occurred in the rumen in terms of increased Ca fluxes. However, the exact molecular and regulatory mechanisms have to be examined in more detail. Interestingly, intestinal Pi absorption in duodenum and jejunum was downregulated by lactation on functional level, and in accordance, sodium-dependent Picotransporter type IIb RNA and protein expression were decreased in jejunum. Whether this downregulation of intestinal Pi absorption can be attributed to sufficient Pi supply from endogenous sources or to lactation-induced increased dietary Pi intake has still to be investigated.