1. An examination of changes in weight and body composition in
a flock of free -grazing Scottish Blackface ewes indicated
that, during the greater part of pregnancy, these ewes were
undernourished and catabolizing considerable amounts of
body tissue.2. The nutritional states of ewes from two differently managed
Scottish Blackface flocks were characterized during late
pregnancy in terms of circulating concentrations of plasma
free fatty acids and ketones. Marked undernourishment was
evident in both situations.3. Data collected in a variety of situations supported the
hypothesis that the severity of undernourishment during late
pregnancy is determined principally by foetal weight and the
level of food intake. Within a group of pregnant ewes with
comparable intakes, the general degree of undernourishment is
dependent on the level of intake, and the relative severity
of undernourishment in individual animals is determined by
differences in foetal weight.4. The use of certain biochemical parameters as indices of undernourishment was examined in ewes with artificially induced
hypoglycaemia. It was concluded that nutritional state is
best characterized in terms of that parameter which shows the
greatest response per unit change in either nutrient intake
or nutrient requirement.5. Biochemical parameters were used to control the nutritional states of individual animals in an experiment on the effects of undernourishment during pregnancy on lamb
birth- weight. The results of this experiment indicated
that the undernourishment occurring in free- grazing hill
ewes during late pregnancy was likely to reduce the birth - weight of single lambs by 10%, and that of twins by 25%.6. The additional energy requirements during pregnancy were
estimated to be 100g digestible organic matter per kg
foetus
