1. According to the Agricultural Research Council (1965) energy retention in cattle is predicted from metabolizable energy (ME) intake, the net availabilities of ME for maintenance (km) and for fattening (kf) and measurements made of fasting metabolism (F). The present experiments were designed to examine the validity of the use of F as a basis from which to predict energy retention.

2. Four British Friesian and four Aberdeen Angus steers were fed, from weaning to slaughter at about 450 kg, a barley-based, pelleted diet at two levels calculated to yield overall efficiencies of retention of ME of 20% and 10% respectively. Successive measurements were made of the energy balance of each animal at intervals of 4 to 8 weeks.

3. The metabolizability of the diet was measured for both sheep and cattle. In both species metabolizability was greater at the higher level of feeding. In sheep kf measured directly or estimated from metabolizability was 0·61.

4. Measured values for F in cattle agreed closely with values given by the Agricultural Research Council.

5. Basal metabolism in the growing animal (F') was predicted by extrapolation to zero intake of measurements made on animals in positive energy balance. Log F' during growth was proportional to log body weight0·73. Expressed in terms of the usual exponent of metabolic body size, F' was about 440 kJ/kg0·75 per 24 hr throughout growth. There were no major differences in F' attributable to breed or to level of food intake.

6. The results indicate that F is not a good basis from which to predict energy retention in steers.

A simplified Net Energy system for ruminants is described. It is based on the Metabolizable Energy system outlined by the Agricultural Research Council (1965) and enables a non-iterative approach to be used in the formulation of rations. The method is suitable for use in linear programming work and is illustrated, with appropriate tables, for growing cattle.

A latin square design with three periods of 3 weeks was used to measure the dry-matter intake, live-weight gain and water intake of 12 British Friesian calves offered an all-concentrate diet ad libitumin wet form. The diets contained 30% (B), 20% (C) or 15% (D) dry matter. A further six calves were given the same diet in dry form (A) throughout the experimental period. Digestibility and nitrogen balance were measured on four calves on each treatment at the end of the experimental period. In addition, two Ayrshire calves, each fitted with a permanent abomasal cannula, were used to study the site of digestion of the feed when given in dry or wet form.

The mean dry-matter intakes of the calves given the dry and wet feeds were 75·5 and 80·8 g/kg W0·75 per day respectively and mean daily live-weight gains were 849 g for the calves on both types of feed. The mean dry-matter intakes of the calves given the wet diets were 80·9 (B), 81·2 (C) and 75·5 (D) g/kg W0·75 per day, and the live-weight gains (g/day) were 857 (B), 879 (C) and 812 (D). None of these differences were significant. The intake of water by the calves was significantly increased by reducing the dry-matter content of the diet. The form or dry-matter content of the diet offered had no effect on the digestibility of dry matter (76·1%), organic matter (77·9%), energy (75·8%) or crude protein (75·8%) or on nitrogen retention (32·5% of N intake).

The rumen was the main site of digestion for all Tour diets and an average of only 7% of dietary starch passed undigested through the abomasum.

1. Observations were conducted to ascertain the social dominance structure in two small groups of castrated male Corriedale sheep. In these and a third group, the order of the sheep past a fixed point was recorded, when they were moving either voluntarily or under force. Records were also made of the way in which the sheep distributed themselves spatially in a confined area, relative to one or two men simulating yard work. In a fourth group divided into two sub-groups, the social dominance structure was determined before and after the subgroups were mixed, to assess the effect of mixing.

2. The small groups showed a distinct social dominance hierarchy of a linear type, similar to that found in cattle and pigs. The dominance status of individual animals was correlated with their body weight, wither height and height at hocks. Dominance status within a subgroup remained stable following the mixing of sub-groups.

3. The sheep adopted consistent positions in forced movement, and in relation to one or two men simulating yard work. There was no consistency in voluntary movement. Dominant animals did not lead the forced movement, were usually some distance from man, and were widely scattered from each other.

4. Dominance status was closely related to positional behaviour.

The attachment between the ewe and her lamb, as assessed by estimating the distance between ewe and lamb and observing their behaviour, was studied for the 4 weeks after birth. The ewe and lamb kept in close contact throughout this period. They were within 10 metres of each other in 56% of all observations; only in 6% of all observations were they more than 50 metres from each other. With increasing age of lamb, the ewe spent more time grazing while the lamb also spent more time grazing and playing and less time sucking. The lambs showed independent forms of behaviour such as the formation of groups as they got older. The distinct dependent behaviour traits were that if bothewe and lamb were lying or walking, then they were usually close together.

The mean distance between ewes and lambs remained constant for dependent forms of behaviour but gradually increased with age for independent forms of behaviour.

Over a 15-year period nearly 2000 young females were exposed to the ram at 6 to 9 months of age. These Clun Forest females were born between January and April in the Cockle Park experimental flock, and mated between October and December of the same year. On average nearly 42% of those present at lambing did not produce a lamb. Analyses are presented of the reproductive efficiency of these animals and of some of the possible causes of their failure to lamb. Observations in 10 of these years suggested that only 12% had not been mated and might therefore be assumed to be prepuberal. Age at first oestrus for those animals achieving puberty in their first autumn was inversely related to date of birth. The number which lambed increased by 1·1% per kg increase in live weight before mating.

In 3 years simple nutritional and housing treatments were applied to groups of female lambs. Feeding a cereal supplement to animals at pasture before, during and after mating, and housing 1 to 2 weeks after mating, appeared to increase the percentage which lambed. It is suggested that the effect was to reduce the amount of early embryo death caused by nutritional and climatic stresses on the normal grazing animal.

Cobs and pellets which differed in particle size (modulus of fineness, MF) were prepared from dried perennial ryegrass and tall fescue and given to sheep. The MF values of the feeds were 2·45,1·09,0·81 and 0·74 for perennial ryegrass and 2·28,0·84,0·67 and 0·57 for tall fescue. Organic matter digestibility was similar for the two grass species when measured in vivo, but when measured in vitro values for perennial ryegrass were about 3 units higher than those for tall fescue. Voluntary intake and live-weight gain were higher for sheep given tall fescue, the difference in live-weight gain being just significant at P < 0·05. The response to change in particle size was similar for the two grass species. Intake was lowest and digestibility highest for the feeds with the highest MF, but differences between the three finely-ground forms of each species were not significant. There was a tendency for the intake of digestible organic matter to be lower for the feeds with lowest MF than for those with intermediate values for MF. The rate of passage of undigested particles was slower for cobs with the highest MF than for the other feeds, which did not differ significantly one from another.

Shorn Blackface sheep were acclimatized to cold by acute or chronic exposures. Acclimatization caused increased resistance to body cooling (IRC) during acute exposure and elevated heart rates at thermoneutrality (28°C). The length of time these effects were retained during subsequent periods at thermoneutrality was monitored.The effect of moderate heat stress (36°C) on previous cold acclimatization was also measured in Blackface and Merino sheep.

Conclusions were:

1. IRC resulted from previous exposure to chronic cold or acute cold. IRC induced by chronic cold began to decay after 2 weeks at thermoneutrality. IRC induced by one acute exposure was maximal 2 weeks after exposure and had disappeared by 8 weeks. IRC induced by two acute exposures combined with chronic cold showed little decrease even after 8 weeks at thermoneutrality.

2. Merino sheep showed 50% lower initial cold resistance and smaller IRC following acclimatization than equivalent Blackfaces.

3. Heat stress for 10 days after cold acclimatization had no effect on IRC in Blackfaces or Merinos.

4. Heart rates measured at 28°C were increased by 20 to 50% following acute and chronic cold exposure. After 3 days at thermoneutrality about 70% of the increase remained; but after 8 days almost all the increase had disappeared.

5. Two components of cold acclimatization were distinguished:

(i) Increased resistance to body cooling probably caused by an enhanced peak metabolic rate capability.

(ii) Increased resting metabolic rate evidenced by high heart rates. After the cessation of cold treatment the rates of decay of these two components were different.

1. The experiment was designed to compare the protein and energy metabolism of pigs growing at 25°c or 34°C. The pigs were given two levels of feeding while growing between 25 and 75 kg live weight.

2. The high temperature was associated with increases in rectal temperature of 1·2 to 20°C. Both pigs on the higher level of feeding at 34°C became lame in their hind legs.

3. The high temperature was also associated with increases in heat production and in urinary nitrogen and energy losses for pigs fed at the higher level of feeding only; however fasting heat production was not affected significantly by temperature. The high temperature had no effect on the apparent digestibility of the diet.

4. It was calculated from data for pigs at both levels of feeding kept at 25°C, that efficiency of utilization of metabolizable energy (ME) above maintenance was 71%, and the maintenance requirement for ME was 100 kcal/kg0·75 day. Energy retention was reduced at 34°C in pigs fed on the higher level of feeding.

A simple model is described which enables the prediction of the magnitude and direction of the responses of growing pigs to different energy and protein intakes. The model calculates daily live-weight gain from the conversion of the dietary supply of crude protein and energy into protein, lipid and ash in the body of the growing pig. Values were also determined for the energy and protein balances, the composition of the body and the efficiency of feed conversion. The model was formulated with factors drawn from published findings and validated by comparison with independent feeding trials.

Six lines of mice were fed distinctive fixed or shifting diets while being selected for fast growth in the first two weeks after weaning. The intention was to provide alternative routes for the improvement of growth with respect to a maize diet (100% maize) where controls grew 6 g, an optimum diet (76% maize, 24% milk) where controls grew 17 g, and a ‘milk’ diet (16% maize, 84% milk) where controls grew 12 g. After 10 generations of selection the lines, hybrids and unselected controls were compared on these and intermediate diets. Realized genetic correlations between growth on optimal and suboptimal diets depended on the feeding regime in which selection was practised, and were significantly higher in lines that were selected on suboptimal diets. When the selected lines were tested on unfamiliar suboptimal diets they were hardly better than controls, but on their own diets and also on the optimum diet were about 6 g heavier. Peak growth was never much greater than on 76% maize and was made on diets containing between 58% and 82% maize. With one exception, the hybrids grew on each test diet about as well as did the best selected line.

A genetic limitation was encountered on the optimum diet. The growth there of the mice selected on either milk or maize diets was not improved upon by the mice actually selected on the optimum diet.

The digestibility and N contents of samples collected by oesophageally-fistulated sheep and by hand plucking were compared. Hand plucking overestimated nutritive value at high levels of digestibility and N content, and underestimated nutritive value when this was low. The differences between fistula and hand-plucked samples varied between pastures. Precision was increased when samples were combined between operators.

In two experiments carried out on 36 crossbred growing lambs the effect of purified bovine somatotrophic hormone (STH) on wool production and some qualitative fleece characters was studied. Food intake during and after the hormonal treatment was also examined. STH, injected in a dose of 1 mg/kg of body weight in 10- or 15-day intervals to growing lambs from 2 to 100 days of age, increased fleece weight significantly. This increase was accompanied by considerably higher daily food intake both during the hormonal treatment and 15 weeks after cessation of STH injections. No significant effect of STH on qualitative fleece characters was found.