Blood lactose v. milk lactose as a monitorof lactogenesis and colostrum production in Merino ewes

Abstract

The pattern of onset of lactation and colostrum production was compared in 42 single-and twin-bearing Merino ewes of 2 genotypes, Australian Merino Society (AMS) or Meridale (AMS with an infusion of British Breeds). The onset of lactation was indicated by measuring changes in the concentration of lactose in udder secretions (milk lactose) and in blood 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 was a novel alternative to milk lactose, as blood was easier to collect than udder secretions. Colostrum production was measured by milking the ewes at 1, 3, and 6 h after parturition. Twin-bearing ewes initiated lactation later than single-bearing ewes, but both groups produced similar volumes ofcolostrum to 1 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). Meridale Merinos secreted colostrum at a faster rate than the AMS Merinos at 1-6 h post-partum (94 v.67 mL/h, P < 0·05), but had similar accumulations of colostrum to the AMS Merinos before birth. Five percent of ewes had no colostrum available 1 h after birth. The concentration of blood lactose reflected changes in milk lactose prior to, but not after, the first few hours post-partum. Blood lactose concentration measured prior to birth was related to the volume of colostrum that had accumulated in the udder up to 1 h after birth (r = 0·60, P < 0·001), but milk lactose measured at the sametime was not related to the accumulation of colostrum. Blood lactose measured before birth can beused to estimate whether treatment groups of ewes differ in the volume of colostrum available for the lamb at birth. This may permit us to study the relationship between lamb survival and colostrum production in the field without disturbing the ewe-lamb bond by milking the ewe.