Ruminant ketosis.

Female ruminants are susceptible to spontaneous ketosis arising at times of high productive demand. The dairy cow is most susceptible during the first 7 weeks of lactation, whereas the ewe is susceptible, particularly when multifoetate, during the last month of pregnancy. The disorder is characterized by signs of carbohydrate insufficiency and adipose-tissue mobilization. Those of carbohydrate insufficiency include, in the cow at least, hypoinsulinaemia, hypoglycaemia and decreased hepatic content of glycogen and glucogenic metabolites, and those of fat mobilization include increased circulating concentrations of NEFA* and ketone bodies, and fatty infiltration of the liver (Baird, 1977). Similar, but less marked, signs of energy deficiency are evident even in clinically healthy animals during these periods of ketosis susceptibility. At these times, too, ruminants are most susceptible to food-deprivation ketosis, the biochemical features of which are in many ways similar to those of the spontaneous condition (Baird, 1977) (see Table 1). One difference is, however, that although hepatic gluconeogenesis invariably falls during food deprivation, it may remain within the normal range during the initial stages of spontaneous ketosis in cows (Kronfeld, 1971). Non-productive, i.e. non-pregnant, non-lactating, dairy cows seem to be rather resistant to food-deprivation ketosis, and in this way appear to differ from non-productive rats (Table 1). A further apparent difference between dairy cows and rats is indicated by the observation that rats can be more resistant to food-deprivation ketosis during lactation than at other times (Table 1). However, the response of the lactating rat to food deprivation, like that of the lactating cow, depends on the stage of lactation. Thus, although hepatic ketogenesis is low in rats at peak lactation (10-17 days post partum), it is relatively high in rats in early lactation (2-4 days post partum) (Whitelaw & Williamson, 1977). The physiological status of the ketosissusceptible cow is probably more comparable with that of the latter group, in view of the duration of lactation in the two