1. Two experiments have been performed to compare the performance of pigs given cool ‘whey’ (15°C) with that of pigs fed warm ‘whey’ (40°C). Pigs were penned individually and the ‘whey’ was reconstituted from concentrated materials.

2. In both experiments pigs offered cool ‘whey’ grew at a slower rate and required more dry matter/kg live-weight gain than pigs offered warm ‘whey’; the differences in rate of gain were 11 % at 16°C air temperature in Experiment 1 and 5% at 22°C air temperature in Experiment 2.

3. It was estimated that the ‘heat of warming’ for the cool ‘whey’ might have accounted for its entire effect on rate of gain.

In three similar experiments, 2 or 3 kg of a commercial concentrate mixture, forming part of a high concentrate ration, were replaced by an equal weight of dry matter of one of four roughages: hay, straw, silage and green soilage.

The metabolizable energy content of the concentrate was 2-4 Mcal/kg. Expected daily gain was calculated according to the following energy systems: Scandinavian feed units (SFU), starch equivalent (SE), total digestible nutrients (TDN), the U.K. Agricultural Research Council system (ARC), and the U.S. National Research Council net energy system (NRC).

The replacement of 2 kg of concentrate significantly reduced daily gain only in the straw treatment. Reduction of the fat content of the carcasses was significant for all roughage treatments. The differences between the observed daily gain and the expected, as calculated by the SFU, SE and NRC systems, were highly significant, while those between the observed and those cal culated by the TDN and ARC systems were not significant. The TDN system overestimated the nutritional value of the roughages, while the SFU and SE systems underestimated it.

A numerical model of male and female replacement processes in a dairy cattle population was constructed in order to describe the long-term genetic and financial consequences of selection amongst bulls in AI.

Changes with time in the relative contribution of different generations of offspring to the total genetic improvement of the population were described. It was shown that the genetic change resulting from a single selection process amongst the males eventually approaches an equilibrium many years after selection is practised. Owing to the delays involved in the progeny test, individual males made no genetic contribution for a period of 10 years and a small but constant contribution thereafter.

The costs of bull testing and selection, and the monetary benefits obtained from it, were estimated. Current selection procedures proved to be highly profitable at prevailing market prices. Capital invested in the testing programme was recovered within 2 to 5 years of the first offspring calving.

The effect of changes in milk prices and feeding costs on monetary returns was examined. It was concluded that sire testing programmes are likely to prove unprofitable only under extremely adverse economic conditions.

A theoretical study is reported of the way in which additive genetic improvement, made in a nucleus population, is passed to successive levels in a three-tier multiplication system. The rate at which progress accumulates at each level is approximately equal. The extent to which each tier is genetically behind the previous one has been termed the ‘improvement lag’. These lags can be considerable; their actual size is determined by the annual rate of progress in the nucleus, the age structure in the lower tiers, and by the origins and degree of selection achieved in the animals used as parents in these tiers. Only improvements generated in the top tier are cumulative. The scope for reducing the improvement lag is discussed within the context of livestock production in Britain.

Data were obtained from 27 pure Shorthorn, 22 Angus × Shorthorn, 31 Charolais × Shorthorn and 27 Hereford × Shorthorn cows, during 10 years. Angus × Shorthorn cows required the least number of services per conception (1·17), had the shortest average gestation lengths (280·6 days), and had a calving percentage of 88·2% and birth weight of calf of 29·8 kg. The respective figures for Charolais × Shorthorn were 1·21 services, 281·6 days, 88·3% (the highest) and 32·9 kg (the heaviest), for Hereford × Shorthorn 1·23 services, 283·6 days, 84·4% and 31·6 kg, and for pure Shorthorn 1·20 services, 282·2 days, 82·7% and 29·6 kg. Average calf weight at birth increased with the advance in age of cow up to 5 years, then showed little change. Seventy-two per cent of the crossbred cows calved for the first time at 2 years old compared with 65% of the Shorthorns. On the other hand, Shorthorn cows had the highest twinning percentage (2·9%) and the lowest single calf mortality at birth (1·4%). The maximum body weights of Angus, Charolais, and Hereford crossbreds and Shorthorn cows were 576·8, 655·8, 6254 and 553·8 kg respectively at 7–8 years of age.

Diets of cooked maize meal and dried skim milk were fed to newly weaned mice for 2 weeks, and to lactating females for 3 weeks. The diets ranged from 16% to 100% maize, with complementary amounts of from 84% to 0% milk and a 5% supplement of yeast.

Live-weight gains from 3 to 5 weeks of age were greatest when an intermediate diet containing 76% maize was fed. Average gains on 16%, 76% and 100% maize were 8·0 g, 17·7 g and 5·5 g respectively. The full sib phenotypic correlation was 0·45 but gains were independent of weaning weight. No carry-over effect was detected from maize-milk diets that had been fed to the dams; the dams' own gains at the same age had little influence on their offspring.

Weight of food consumed per mouse varied little between diets despite marked differences in gain. Food and energy intakes relative to gain showed no trend between 16% and 88% maize but doubled between 88% and 100% maize. Protein was used most economically for gains on 88% maize.

There were health problems. When high milk diets were first used many mice suffered from diarrhoea. A few mice on 95% maize, whose dams had been given the same diet during lactation, died without prior symptoms. Mice on 100% maize were thirsty, but not glycosuric.

Females nursing litters on high milk or high maize diets drew on reserves in the carcass, liver, pancreas, spleen and fat. In addition, high milk diets caused hypertrophy of kidneys and caecum, and diarrhoea.

1. Eight British Friesian male calves were fitted with rumen cannulae at 4 weeks of age, and were given either chopped or pelleted dried grass to appetite. After weaning at 6 weeks the animals were allowed to eat to appetite, or the appropriate food material was added via the cannula, or digesta removed, at the rate of 20 % (dry-matter basis) of voluntary food intake, in alternating periods of 7 days.

2. The addition of food material resulted in a depression in drymatter intake (DMI) which was greater than the increase in DMI following the removal of digesta, and the difference approached significance in the small number of comparisons possible.

3. The response in voluntary food intake increased significantly with age, and reached or exceeded ‘adult’ levels within 6 weeks from weaning. It is postulated that oropharyngeal factors associated with the development of eating behaviour control the initial development of solid food intake; the influences of physical or metabolic limitations upon food intake increase with time.

The influence of breed and sex on relative growth patterns of muscle, bone and fat in beef cattle has been investigated. Comparisons were made of growth coefficients estimated using Huxley's (1932) allometric equation relating muscle, bone or fat to muscle plus bone using data from the dissection of half carcasses of 63 young bulls, 106 steers and 22 heifers representing a number of breed groups. Growth coefficients for muscle and for bone were found to be similar among different breed groups of bulls, steers and heifers. The proportion of muscle increased and that of bone decreased as the size of animal, measured by muscle plus bone, increased. Muscle and bone weights adjusted to common muscle plus bone weights were significantly different among breed groups within sex. Differences in amount of muscle relative to bone were therefore established at earlier stages of growth and maintained over the period represented in the present study.

Growth coefficients for fat were significantly different among breed groups within sexes.

Sex within breed group had no statistically significant influence on growth coefficients for muscle or for bone. Muscle and bone weights adjusted to a common muscle plus bone weight were similar for sex groups within all breed group comparisons. Sex did not have a marked effect on rate of fattening since differences between growth coefficients for fat (between sexes, within breeds) were not statistically significant—although in all comparisons growth coefficients for fat were lowest for bulls, intermediate for steers and highest for heifers. Sexes differed in weight of fat adjusted to common muscle plus bone weight, heifers being fatter than steers and steers fatter than bulls, a difference probably resulting more from early onset of the fattening phase in heifers, followed by steers, rather than relative rate of fattening.

Reconstituted milk substitute was given at two concentrations of powder (10% and 20%), each at four levels (10% powder—8, 12, 16 and 20% of live weight (LW); 20% powder—6, 8, 10 and 12% of LW) to 3 British Friesian male calves per treatment from 2 to 4 weeks after arrival, and the calves were weaned over the next 7 days. Chopped dried grass was offered to appetite before and for 3 weeks after weaning. The amount of solid food eaten was not affected by the dry-matter concentration of the milk substitute, but was significantly depressed as the amount of milk consumed increased. Between-treatment differences in solid food intake established at weaning persisted until the end of the experiment. There was a dose, positive relationship between milk intake and live-weight gain (LWG) before weaning, but weight gain after weaning was not significantly affected by the level of milk intake before weaning.

The incidence of abortions over a period of eight years was studied in 107 393 progeny of 100 bulls belonging to five dairy and three beef breeds of cattle. The calving records related to the first four artificial inseminations on females with fresh or frozen semen.

The average frequency of abortion was 2·12%. Differences in rates of abortion between the breeds of sire were statistically significant although this may be confounded with the breed of dam. The highest incidence was from matings by bulls of the Channel Island breeds and the least from matings to Ayrshire bulls.

The rates of abortion increased with the number of inseminations necessary for conception.

There was a slightly higher incidence of abortions among twin births than among singles.

Effects of constant and of changing diets on responses to selection were studied. Mice were fed maize meal and dried skim milk from 3 to 5 weeks of age and were selected for live-weight gains in that period. Gains in the generation prior to selection were 17·7 g on 76% maize (24% milk), 8·0 g on 16% maize and 5·5 g on 100% maize.

The Fixed optimum line was selected on 76% maize, the Milk line on 16% maize and the Maize line on 100% maize. The diets of three other lines were reviewed at each generation, and two diets were fed on each occasion. The diets of the Shifting optimum line straddled the optimum of the previous generation; those of the Milk-impelled line at first had a little more than the optimum amount of milk, but were made more milky as normal growth resumed; and the Maize-impelled line was similarly directed towards 100% maize. Back selected milk, optimum and maize sublines were taken off the three lines on constant diets. The Control line measured unimproved rates of growth on 16%, 52%, 76% and 100% maize.

Dietary effects were not always repeatable. Controls on the optimum diet, 76% maize, were the most stable across generations and with this diet, gains generally had the lowest phenotypic variance within generations —g2. With 100% maize, this variance was slightly larger—8 g2. The diet with the least stable effect was 16% maize; as Control gains rose from 8 to 15 g, phenotypic variance fell from 21 to 6 g2. On various diets between 88% and 96% maize, the variance of the Maize-impelled line rose from 6 to 34 g2 without commensurate changes in its mean gain.

Responses of generally about 5 g above controls were made in five generations of selection. The Maize line was exceptional in making no forward response. Heritability of growth between forward and back selected sublines was highest on good diets (0·49 on 76% maize) and lower on poor diets (0·20 on 16% maize and 0·28 on 100% maize).

The Fixed and Shifting optimum lines do not as yet differ on comparable diets; nor the Milk and Milk-impelled lines on 16% maize. The Maize-impelled line has not yet been tested on 100% maize and cannot be compared with the Maize line. Family-by-diet interactions were smaller than consistent family differences. It is concluded that genotypic improvements may be effective over a wide range of maize-milk diets.

1. British Friesian male calves were offered reconstituted milk substitute four times a day in steadily increasing quantities, so that the amount offered exceeded appetite after 14 days. They were given one of three dried herbage diets (pellets P1 and P2, and untreated material H2 made from the same crop as P2) to appetite, either from the start of the experiment (Treatment A) or from the start of weaning (Treatment W) 21 days after arrival. The experiment was terminated six weeks after the calves were weaned.

2. Grinding and pelleting (P2 v. H2) markedly reduced the in vivo digestibility of the diet, and the time of retention in the alimentary tract, increased the voluntary dry-matter intake by 50% and live-weight gain of the calves by 100%. The intakes of the two pelleted diets were similar.

3. The intake of diet H2 after weaning was greater in calves which had experience of the diet before weaning than in those which did not, but the intake of the pelleted diets was not affected by previous experience of solid food. The time required to eat unit weight of dry matter was four times as long for diet H2 as for the pelleted diets, and there were similar differences between diets in ruminating time. It is suggested that the development of solid food intake is influenced by the ease with which the diet can be eaten.

4. The initial increase in solid food intake after weaning was related to an increase in the times spent eating and ruminating, but later increases in food intake were achieved with no further increases in eating or ruminating time.

1. An experiment was conducted with dairy cows over two grazing seasons to investigate the feasibility of fixed rotational grazing. Each year a comparison was made between treatment A, which consisted of four equal paddocks grazed for 1 week and rested for 3, and treatment B, which contained five paddocks grazed for 1 week and rested for 4. The influence of the length of the rest periods on output per hectare and per cow was measured. Within each paddock approximately one-seventh of the area was allocated daily to each treatment group, there were no back fences and the paddocks were not topped or harrowed. Stocking rates were identical on both treatments at all times at 6·2 cows per ha throughout 1964; 7·1 cows per ha for weeks 1·9 inclusive and 6·2 cows per ha for weeks 10·20 inclusive in 1968. The fertilizer nitrogen applied (282 kg/ha) was equivalent to a daily rate of 2·02 kg/ha. The feed intake of each cow was measured on three occasions during 1967 and four in 1968.

2. Differences between treatments in outputs per ha were small and on average about 13 000 kg milk and 890 cow grazing days were produced per ha during the 20-week experimental period.

3. Differences between treatments A and B in herbage intake, milk production, milk composition and live-weight change were not statistically significant.

4. When 3·6 kg of a supplementary concentrate was given to some cows, positive responses in milk production, milk composition and live-weight change were found, but the value of the extra milk produced was less than the cost of the concentrate.

A comparison was made of beef-type and dairy-type suckler cows in 17 herds by forming pairs when cows of both types calved within 7 days of each other in the same herd. Cows and calves were weighed within 14 days post partum and when turned out to grass. The calves were weighed again at weaning. Winter food intakes were recorded by weighing feeds on one day of each month. Sixtynine pairs of cows were formed and 23 different levels of winter food input to the cows were computed.

Calves out of dairy-type cows were significantly heavier at turn-out (8-4 kg) and at weaning (8-3 kg). These differences were greater at higher levels of winter food intake per cow.

A variety of energy and protein supplements for winter diets based on barley straw were tested in experiments carried out over three years with spring-calving suckler cows. All the supplements resulted in satisfactory calf weaning weights and cow performance but there were indications that a low level (2·3 kg) of barley plus 68 g urea adversely affected the birth weights of calves and their performance from birth to turnout.

1. Two experiments are described in which polyethylene glycol was used to estimate the volume of fluid in the rumen of calves weaned at an early age from milk substitute on to diets of dried grass.

2. The limitations of the technique in relation to studies on voluntary food intake are discussed.

3. Linear relationships were observed between the volume of rumen fluid and the consumption of solid food within each of three diets, as solid food intake increased after weaning.

4. In one experiment, the concentration of dry matter in the rumen contents increased by 50% over the first 3 weeks after weaning. There was no significant change with time after weaning in the pH or the digestive efficiency, measured in vitro, of samples of rumen contents.

5. The times spent eating and ruminating increased rapidly after weaning on both a long and a pelleted diet, but then remained relatively constant despite continued increases in solid food intake. Eating and ruminating times were much greater for the long than for the pelleted diet.

The discounted cash flow procedure of management accounting is used to evaluate national breeding programmes. Alternative methods of improvement of meat production from cattle born in the dairy herd are taken as examples. These schemes utilize selection for beef characters either in the dairy breed itself or within a beef breed, maintained in a small herd and used as a source of bulls for crossing by AI. In each case young bulls are selected for growth rate in a performance test, which precedes the progeny test for milk production in the dairy breed.

Greater rates of genetic progress and monetary returns are predicted from improvement of the beef breed, but both schemes are expected to yield a return on investment of over 15%. The net returns from the programme in the beef breed are influenced less by changes in assumptions.

Approximate, but simple, methods of computing the discounted returns are described.

1. Jersey calves were fed on milk substitute at the rate of 10% of live weight per day for 5 weeks and were offered either chopped dried grass or ground, pelleted dried grass to appetite. Calves were slaughtered at birth and after 5, 6, 7, 9 and 12 weeks on experiment, and the weights of the component parts of the alimentary tract and their contents were measured.

2. There were close correlations between the weights of the sections of the alimentary tract or their contents and the solid food intake at slaughter, total solid food intake, or empty body weight of the calves. There were no consistent changes with age in the DM concentration or the density of the digesta in any section of the alimentary tract except the abomasum, or in the digestibility or mean retention time of the diets.

3. Grinding and pelleting the diet increased the DM concentration but did not affect the density of the digesta. The increase in the weight of rumen contents per unit increase in dry-matter intake was much greater for chopped than for pelleted diets. The reverse was true for the contents of the abomasum and small intestine. There were relatively small variations between diets in the predicted weight of rumen contents, total digesta, or the volume of organs in the abdomen, at the within-diet mean levels of dry-matter intake.

Twelve British Friesian and 12 Ayrshire castrated male calves were fed ad libitum one of three complete diets of differing energy concentration from approximately 140 to 410 kg live weight. Differences in energy concentration of the diets were achieved by inclusion of different proportions of wet distiller's grains (WDG). Increasing the proportion of WDG in the diet caused reductions in performance. This effect was more marked with the Friesians than with the Ayrshires. The treatments had small and generally non-significant effects on carcass conformation and composition.

Two lines of Large White pigs were selected for increased rate of growth and decreased backfat thickness respectively over five generations. Each line was bred from four boars, each mated to four gilts per generation, these being selected on a within-family basis to minimize inbreeding. Response to selection was measured by direct comparison with contemporary control stock. The control line, originating from the same foundation stock as the selection lines, consisted of 15 groups of one boar and two gilts, mating between groups being designed to reduce the rate of inbreeding.

Over three generations the control stock exhibited random variation in the traits measured except rate of daily live-weight gain and backfat thickness ‘K’. The evidence suggests that the time trend in these was mainly, if not entirely, non-genetic in nature.

The low rate of progress achieved in both lines is ascribed to the selection method adopted and to losses of potential breeding stock. It is concluded that the success of such a small-scale breeding operation is dependent on achieving optimum husbandry conditions, and even then it cannot achieve the same rate of progress as in larger herds. The necessity of using a control strain to assess genetic progress in experiments of this nature is emphasized.