Effects of Osmotic and Hydrostatic Pressures on Milk and Antimicrobial Substance Production in Lactating Goats

Osmotic and hydrostatic (intramammary pressure) pressures within the mammary gland may stimulate mammary epithelial cells and leukocytes, which alter milk production and immune functions. We aimed to clarify the effects of different volumes and concentrations of NaCl solution on milk and antimicrobial substance production in lactating goats. Intramammary infusions of different NaCl solution concentrations (0.9% and 2.7%) at different volumes (50 mL or until full in the udder) were carried out; milk samples were collected for 5 days after infusion. The infusions resulted in significant daily effects on milk yield, somatic cell count (SCC), sodium ion (Na⁺) and potassium ion (K⁺), milk amyloid A (MAA), S100A7, and lactoferrin (LF) concentrations. Sodium and potassium ions, SCC, and MAA levels differed depending on the infused volume, whereas those of S100A7 and LF differed according to the NaCl concentration. These results suggest that short-term increases in hydrostatic and osmotic pressures modulate milk production and stimulate antimicrobial factor production in the mammary glands. Hence, they highlight a potential approach toward enhancing innate immune function in the udder.