Secretory activity of goat mammary glands during pregnancy and the onset of lactation.

Abstract

SUMMARY1. The volume of the udder and the composition of the secretion have been followed in five goats through pregnancy to the onset of lactation.2. During the middle of pregnancy udder volume was minimal and there was little or no fluid in the teats.3. Two stages of commencing secretary activity (lactogenesis) were defined. In the first, starting up to ten weeks pre-partum, udder volume increased and the fluid in the teats changed from an extracellular-fluid-like to a milk-like composition and acquired a high concentration of immunoglobulins. Four goats accumulated several litres of a pre-colostral fluid with a high [lactose] 6-7 weeks pre-partum.4. Comparison of the rate of increase in udder volume with previous data for the rate of increase in empty udder volume in pregnant goats showed that the rate of secretion, even in the last few days of pregnancy, was only a few per cent of the rate immediately after parturition.5. In the last 2-3 days of pregnancy there was a three to elevenfold increase in [citrate] in the secretion; this heralded the onset of copious secretion at about the time of parturition.6. The changes in mammary gland activities are discussed in relation to changes in plasma hormone concentrations during pregnancy.

Effects of continuous lactation and short dry periods on mammary function and animal health

“…Colostrogenesis can be characterized by both morphological and biochemical changes that occur in two stages (Fleet et al, 1975;Oliver and Sordillo, 1988). The first stage occurs over the last 2 weeks of the dry period when the volume of pre-colostral fluid in the mammary gland cistern increases slowly.…”

“…IgG 2 plays an important role in opsonophagocytosis of bacteria by PMNs and in antibodydependent PMN cytotoxicity (Butler, 1983;Detilleux et al, 1994). The second stage begins immediately before parturition when copious colostral secretion occurs (Fleet et al, 1975). The concentration of Igs falls with the onset of copious secretion and accumulation of secretions in the gland.…”

Lactose and major milk proteins are present in secretory vesicle-rich fractions from lactating mammary gland.

“…This article must therefore be hereby marked "advertisement" in accordance with 18 (28). Electrophoretic separations were also made in 4 M urea/polyacrylamide gels according to Groves and Kiddy (29).…”

Local production of prostaglandins in relation to mammary function at the onset of lactation in the goat.

“…there was a significant and marked decrease over the 48 hr before parturition. Citrate concentration in mammary secretion showed a marked increase from 3 days prepartum to term, as previously described (Peaker & Linzell, 1975;Fleet et al 1975;Davis et al 1979). The changes in concentrations of the major components of the aqueous phase of milk showed similar changes to those previously described in PROSTAGLANDINS AND LACTOGENESIS Linzell & Peaker (1974), namely [Nal and [Cl] decreased while [lactose] and [K] increased near term.…”