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Subterranean clover (Trifolium subterraneum L. cv. Clare) was harvested before flower emergence and dried rapidly without heating. Each of four adult sheep was given the dried clover at rates of 200, 600, 1000, and 1400 g/day in four successive fortnights and was finally fed ad libitum for 1 month. Energy, nitrogen, and carbon balances and body weight changes were measured. The fasting energy losses of the sheep were determined at the end of the experiment. The hay contained approximately 27% crude protein, 14% crude fibre, and 3% lignin (dry matter basis) and was eaten avidly by the sheep. Voluntary consumption ranged from 1400 to 2100 g dry matter/day, and maximum balances were 2080 kcal and 17 g nitrogen/day. Digestibility of energy was 78% at the lowest level of feeding and 74% at the highest. Cell wall and cell contents were respectively 74 and 82% digestible. Energy losses in methane were unusually low (7–11% of digestible energy) whereas losses in urine were unusually high (12–21%). The net result was that metabolizable energy was a lower fraction of digestible energy than for most forages, e.g, it was c. 77% at maintenance instead of the normal 82%. Net availability of metabolizable energy was 84% between fasting and half maintenance, 69% between fasting and maintenance, and 54% above maintenance. The value of this clover per gram was in keeping with its chemical composition and digestibility; its exceptional value as a feed was due to the large amounts of digestible energy which the sheep took in when fed ad libitum.

Energy, carbon, and nitrogen balances were determined in adult wether sheep given a diet of lucerne hay and whole oats at several planes of nutrition between fasting and ad libitum. Four sheep were studied when their weight was c. 30 kg (10% fat) and later when they weighed c. 75 kg (33% fat); another four were studied at c. 70 kg (30% fat) and later at c. 45 kg (16% fat). The most obvious effect of fatness was loss of appetite. Voluntary food intake began to decline when body weight approached 60 kg and was half of the maximal amount when the sheep weighed 70 kg or more; one very fat sheep ate only 100–200 g food/day for several weeks. 1n addition, environmental changes such as transfer from a pen to a cage or respiration chamber often caused temporary inappetence when the sheep were in fat condition but seldom when they were lean. Fasting metabolic rate increased with body weight in accordance with the relationship generally applicable to adult sheep except when the sheep were in the anorectic phase of obesity, at which time their metabolic rate was 30–40% above normal. The digestibility of the diet was not dependent on the fatness of the sheep, nor was the relationship between metabolizable and digestible energy. At each level of feeding, the heaviest sheep produced most heat, but differences were less than at fasting; oxidation of fat, rather than protein, was responsible. When daily heat production and metabolizable energy were both expressed as multiples of the fasting energy loss, all sheep conformed to one relationship; the same held for the relation between energy balance and metabolizable energy. Net efficiency (change of energy balance divided by change of metabolizable energy intake) was 78% for maintenance and 55% for production, irrespective of body condition. Gross efficiency (energy storage divided by gross energy intake) was strongly influenced by body condition. When fed ad libitum, thin sheep achieved an efficiency of c. 26 % and fat sheep reached 21 % whereas anorectic very fat sheep never exceeded 10%. Thin, fat, and very fat sheep required 400, 500 and 650 g dry matter/day respectively for maintenance (zero gross efficiency).

The nitrogen metabolism of five non-pregnant ewes and 16 pregnant ewes was studied. The aim was to examine the effects of pregnancy on the response to severe undernutrition. Some measurements of energy metabolism and blood composition were also made. Pregnant ewes excreted less urea nitrogen in the urine than did non-pregnant ewes when they were all well fed. When food intake was reduced by 75%, excretion by the non-pregnant ewes declined, whereas excretion by the pregnant ewes declined less or increased. After 5 days on the lower ration, pregnant ewes excreted up to 9 g more urea nitrogen daily than did non-pregnant ewes. Urea clearance was constant throughout and was 30–40% of creatinine clearance. Undernutrition caused hypoglycaemia and hyperketonaemia in the pregnant ewes only but there were no clinical signs of pregnancy toxaemia. The heat production of pregnant ewes declined when their ration was reduced. The estimated heat increment of pregnancy was greater with the reduced ration than with the large ration and it is suggested that this change represented the energy cost of gluconeogenesis and ketogenesis from protein. The gross energy content of protein apparently oxidized was estimated to be about 20% of the energy requirement of the foetus. The effects of pregnancy on nitrogen and energy metabolism and on response to undernutrition were approximately proportional to the birth weight of the lamb, and were smaller 7 weeks before lambing than 2 weeks before lambing.