Studies on the carbohydrate metabolism of sheep. I. The range of blood-sugar values under several conditions

Abstract

The considerable volume of literature dealing with the normal range of blood-sugar values in ruminants and with the effect of varying nutritive conditions upon it is reviewed in some detail. Attention is drawn to differences between ruminant and non-ruminant mammals, and an attempt is made to explain them in the light of present knowledge of digestive processes in the ruminant. Data are presented on the normal range of blood-sugar values in sheep, both in Australia and in England, and on the effect of nutritive factors and of pregnancy on these values. The mean blood-sugar values determined by the author in non-pregnant ewes in Australia and in England were 34.8 ± 3.06 and 39.1 ± 3.37 mg. per cent. respectively. The observed range in both pregnant and non-pregnant ewes was 18-57 mg. per cent., but 94 per cent. of values fell between 25 and 46 mg. per cent. This range was obtained in sheep bled usually in the morning, before feeding. A delayed rise, which is slight and always below hyperglycaemic levels, was observed after feeding; the afternoon samples showed higher values than the morning samples. Thus, the normal range of blood-sugar values in fed sheep, at any time of day, is considered to be 25-50 mg. per cent. The level of blood sugar was affected neither by the plane of nutrition nor by the bodily condition of non-pregnant ewes. Gestation in ewes in good condition was observed not to affect the level, although evidence was obtained of lowered blood-sugar levels during the last two months of gestation in ewes in poor condition. Expressed as a percentage of the pre-fasting level, the decrease in blood sugar observed during a four-day fast was similar to that observed in non-ruminants, but the response was delayed. Fasting for a period of 24 hours had little effect on the blood-sugar level in non-pregnant sheep in good condition; in many cases there was little change after the period had been extended to 46 hours. On the other hand, a fast of 24 hours' duration produced a marked hypoglycaemia in ewes in poor bodily condition during the last two months of gestation, blood-sugar levels as low as 8.6 mg. per cent. being recorded.