Abstract:
Proc. Aust. Soc. Anim. Prod. Vol. 18 BLOOD LACTOSE VERSUS MILK LACTOSE AS AN INDICATOR OF LACTOGENESIS IN THE EWE D.M. McNEILL* and P.M. MURPHY* Changes in the concentration of lactose in the secretion from the udder is an accepted monitor of lactogenesis (Hartmann et al, 1973; McNeil1 et al. 1988). However, it is often difficult to express a sample of secretion from the udder before birth. Blood lactose offers an alternative indicator of lactogenesis because lactose leaks into the blood stream from the udder. Forty-two Merino and Merino cross ewes which lambed over a nine-day period were studied. The concentration of lactose in the udder secretion was used to indicate the onset-of lactogenesis (Hartmann et al. 1973), and was measured on a 1 ml sample of udder secretion collected on the day before, and then again at 1 hour after birth. Samples of jugular vein blood (5 ml) were taken at the same time as udder secretion samples, and analysed for plasma lactose concentration (Arthur et al. 1984). Colostrum `production prior to birth was estimated by hand-milking the left side of the udder at 1 hour after birth, immediately following an injection of 2 IU of oxytocin. The lamb was denied access to the left teat during this time. Regressions between concentrations of lactose in the blood or udder secretion (X), and the volume of colostrum produced in the udder up to 1 hour after birth (Y) were calculated. The amount of colostrum present 1 hour after birth can be estimated from the amount of lactose present in either the blood or the udder before birth (see Table 1). Both measures are equally good. However, when measured at 1 hour after birth, milk lactose was the better indicator of prenatal accumulation of colostrum as it had a higher r* value and a lower standard error for its regression coefficient than did blood lactose (Table 1). Table 1 Relationship between concentration of lactose in udder blood (X values) measured 24 h before birth (day -1) birth, and the volume of colostrum accumulated in left before, and up to 1 h after birth (Y). Standard errors coefficients are in brackets. secretion and or 1 h after side of udder of regression When measured before birth, blood lactose and milk lactose are equally good indicators of lactogenesis. However, blood lactose has an advantage because blood is easily sampled whereas, for lactose analysis, a sample of udder secretion is difficult to express before birth. Milk lactose is the better indicator when measurements are made soon after birth. The measuring of blood lactose before birth could be of practical value, as it can be used to estimate the amount of prenatal colostrum without milking the ewes and subjecting them to stress. Such a technique would be useful in relating lamb survival in the field to colostrum production, without disturbing the critical bonding period that occurs in the few hours after birth between the ewe and the lamb. ARTHUR, P.G., POTTER, J. and HARTMANN, P.E.(1984). Proc. Aust. Biochem. Soc.16:12. HARTMANN, P-E., TREVETHAN, P. and SHELTON, J.N. (1973). J.Endocr. 59:249, McNEILL, D.M., MURPHY, P.M. and PURVIS, I.W.(1988). Proc. Aust. Soc. Anim. Prod. 17:437. * School of Agriculture, University of W.A., 525 Nedlands, W.A. 6009.