In-vivo studies of mammary development in the goat using magnetic resonance imaging (MRI)

Summary. Mammary development and regression were measured in goats in vivo using magnetic resonance imaging (MRI). Measurements were made during the first and second cycles of pregnancy, lactation and involution. In primiparous goats, an exponential pattern of growth was evident during ges-tation and for the first 2 weeks of lactation. Parenchyma volume correlated signifi-cantly with milk yield across goats during early lactation, and across stage of lactation within goats. Milking was discontinued in Week 26 of the first lactation. Involution was characterized by an initial accumulation of fluid (over 2 days) followed by re-absorption; parenchyma volume did not decrease significantly until the 3rd week of involution, which was also the time at which these goats were mated to start their second gestation. Their udders still contained significant quantities of fluid (40\p=n-\60%of the gross volume), but parenchyma volume was also greater (by 4\m=.\7-fold)than in goats beginning their first gestation. By Week 15 of gestation there was no longer a parity difference in parenchyma; the udders of first-gestation goats had grown significantly, but those of second-gestation goats had not. Conversely, between gestation Week 15 and laction Week 2 mammary growth was significantly more rapid in the second cycle, such that the udder was larger at the start of the second lactation