BLOOD LACTOSE V. MILK LACTOSE AS A MONITOR OF LACTOGENESIS AND COLOSTRUM PRODUCTION IN MERINO EWES

The pattern of onset of lactation and colostrum production was compare d in 42 single- and twin-bearing Merino ewes of 2 genotypes, Australia n Merino Society (AMS) or Meridale (AMS with an infusion of British Br eeds). The onset of lactation was indicated by measuring changes in th e concentration of lactose in udder secretions (milk lactose) and in b lood samples (blood lactose) collected daily for at least 4 days prior to, and at 1, 3, 6, 12, and 24 h after, parturition. Blood lactose wa s a novel alternative to milk lactose, as blood was easier to collect than udder secretions. Colostrum production was measured by milking th e ewes at 1, 3, and 6 h after parturition. Twin-bearing ewes initiated lactation later than single-bearing ewes, but both groups produced si milar volumes of colostrum to I h after birth (475 v. 371 mL, P > 0.05 ). The rate of secretion of colostrum was similar for twin-and single- bearers in the interval 1-6 h after birth (82 v. 79 mL/h, P > 0.05). M eridale Merinos secreted colostrum at a faster rate than the AMS Merin os at 1-6 h post-partum (94 v. 67 mL/h, P < 0.05), but had similar acc umulations of colostrum to the AMS Merinos before birth. Five percent of ewes had no colostrum available Ih after birth. The concentration o f blood lactose reflected changes in milk lactose prior to, but not af ter, the first few hours post-partum.-Blood lactose concentration meas ured prior to birth was related to the volume of colostrum that had ac cumulated in the udder up to Ih after birth (r = 0.60, P < 0.001), but milk lactose measured at the same time was not related to the accumul ation of colostrum. Blood lactose measured before birth can be used to estimate whether treatment groups of ewes differ in the volume of col ostrum available for the lamb at birth. This may permit us to study th e relationship between lamb survival and colostrum production in the f ield without disturbing the ewe-lamb bond by milking the ewe.