Vasopressin increases milk flow and milk fat concentration in the goat

AIM: The aim of this study was to investigate whether physiological doses of vasopressin affect milk flow and milk composition in goats. METHODS: Six goats were given vasopressin intravenously at doses of 0.1 ng kg(-1) min(-1) (a low dose, VL), 0.3 ng kg(-1) min(-1) (a medium dose, VM) and 1.0 ng kg(-1) min(-1) (a high dose, VH), oxytocin at 10 ng kg(-1) min(-1) and 0.15 m NaCl during 90 min at random. RESULTS: Milk flow increased from 1.3 +/- 0.2 to 3.5 +/- 1.0 g min(-1) (VL), from 1.8 +/- 0.4 to 4.3 +/- 0.6 g min(-1) (VM) and from 1.5 +/- 0.2 to 7.9 +/- 0.9 g min(-1) (VH) during the first 30-min infusions (all P < 0.001), respectively, and then declined. The response to oxytocin corresponded to that of VH. Milk fat concentration increased from 2.1 +/- 0.1 to 3.3 +/- 0.4% during VH and from 2.8 +/- 0.6 to 4.1 +/- 0.6% during oxytocin (both P < 0.001), and tended to increase during VM and VL. The mammary blood flow of four goats was studied with ultrasound during VH and oxytocin infusion. Milk flow increased from 1.8 +/- 0.4 to 4.7 +/- 1.0 g min(-1) during VH and from 1.9 +/- 0.3 to 12.4 +/- 2.4 g min(-1) during oxytocin (both P < 0.001). Mammary blood flow decreased from 262 +/- 37 to 53 +/- 7 mL min(-1) (P < 0.001) during VH, but did not change during oxytocin. CONCLUSION: We conclude that vasopressin increases milk flow and milk fat concentration and suggest that vasopressin, like oxytocin, acts on the myoepithelial cells.