Mammary secretion of oestrogens in the cow

Abstract

Two experiments in vivo and one experiment in vitro were conduced to examine the mechanisms involved, which lead to mammary secretion of oestrogens and its importance for milk production and udder health in cows. In experiment 1 in six cows of the White–Black breed on day 268 of pregnancy catheters were inserted into uterine vein of pregnant horn, the abdominal aorta and the caudal superficial epigastric (milk) vein. Blood samples for estimation of oestrone, oestrone sulphate, oestradiol-17α and -17β by RIA were obtained daily from day 7 pre-partum until day 1 post-partum. Only the concentration of oestradiol-17β was statistically higher ( P≤0.01) in mammary venous plasma than in aortal and uterine plasma. In experiment 2 forty late-pregnant cows were divided into two groups according to their milk production in the previous lactation: group 1 ( n=20) high-yielding cows (>6500 kg milk per lactation), and group 2 ( n=20) low-yielding cows (<3700 kg milk per lactation). Blood samples for measurement of oestradiol-17β by RIA were collected from milk and tail veins every fourth day during a period from day 20 prior to parturition to day 4 post-partum. The concentration of oestradiol-17β was significantly higher ( P≤0.01) in the milk vein than in the peripheral plasma from day 12 pre-partum to parturition. In high-yielding cows the level of oestradiol-17β in mammary venous blood was significantly higher ( P≤0.01) than in low-yielding cows. In six cows with pathological udder oedema ante-partum the concentration of oestradiol-17β in milk vein was significantly higher ( P≤0.05) than in control cows. There were no statistically significant differences in the levels of oestradiol-17β in cows with clinical mastitis ( n=10) during 2 weeks after parturition and without it ( P≥0.05). In an in vitro experiment, homogenates of mammary tissue collected on day 7 pre-partum from two cows were incubated with 3 H -androstendione. After incubation the samples were extracted and 3 H -oestradiol-17β was separated by HPLC. 3 H -oestradiol-17β was formed in a total yield of 37%. These results indicate that oestrone, oestrone sulphate and oestradiol-17α are not secreted by bovine mammary gland. Furthermore, the secretion of oestradiol-17β starts about day 12 pre-partum and is associated with milk yield and udder oedema. Preliminary in vitro study suggests the synthesis of oestradiol-17β by mammary tissue.