Studies on the carbohydrate metabolism of sheep. XIX. The metabolism of glucose, free fatty acids, and ketones after feeding and during fasting or undernourishment of non-pregnant, pregnant, and lactating ewes

Abstract

Average plasma free fatty acid (FFA) values in non-pregnant sheep in widely differing body condition, but fed at levels of maintenance or above, varied from 0.24 to 0.39 m-equiv.11. Values declined after feeding, while blood ketone levels increased. Plasma FFA value is a sensitive indicator of undernourishment in sheep; a pronounced and immediate increase followed a 40% reduction in ration. FFA and ketone levels increased during 7 days of fasting, the former markedly and to a degree depending on blood glucose level; there was a close inverse correlation between plasma FFA and blood glucose levels. Similar correlations were recorded in undernourished pregnant and lactating ewes, although FFA values were consistently higher in lactation at all blood glucose levels. Ketone levels were linearly related to FFA levels when blood glucose values exceeded 25–30 mg %. Below this level of glucose there was no further increase in FFA, but ketones increased markedly. Caloric homeostasis is relatively easily maintained in undernourished nonpregnant and lactating sheep. The undernourished pregnant ewe is susceptible to hypoglycaemia, and it is suggested that there is a critical blood glucose level of 25–30 mg % below which caloric homeostasis becomes more difficult to maintain, because of endocrine changes which markedly affect the normal pattern of fat metabolism.