1. Over the weight range 23–50 kg live weight, pigs were fed either ad libitum or to a restricted scale. From 59 to 91 kg live weight, eight pairs of barrows and eight pairs of gilts were fed on each of two diets varying in nutrient density. The effects of feed restriction, nutrient density of the diet and sex on voluntary feed intake, performance and carcass characteristics were studied.

2. Pigs which had been restricted grew more slowly and contained less fat and more lean at 50 kg live weight.

3. When restricted pigs were offered feed ad libitum from 59 to 91 kg live weight they ate more and had higher daily intakes of digestible energy than pigs liberally fed in early life.

4. There was evidence of compensatory growth in pigs which had received the restricted diet, but there was no significant difference in feed utilization between restricted and ad libitum pigs. It was concluded that the compensatory growth was largely the result of increased appetite.

5. Pigs finally fed on a low energy diet, in comparison with those on a high energy diet, ate more feed but less digestible energy indicating that appetite was physically limited. Efficiency of conversion of digestible energy to live weight was similar on both treatments. A higher proportion of acetic acid was produced in the caecum of pigs fed the low energy diet. Pigs receiving the low energy diet had lower killing-out percentages not entirely caused by differences in the weight of the gut and its contents. The carcasses of pigs on the low energy diet were leaner than those on the high energy diet.

6. Barrows consumed more digestible energy per day than gilts, required more feed and digestible energy per unit live-weight gain, had lower killing-out percentages, shorter carcasses, larger backfat measurements and smaller eye-muscle areas as estimated by A × B measurements. Barrow carcasses contained less dissected lean and more fat than gilts' carcasses.

7. The results are discussed in relation to other work and it is concluded that voluntary feed intake is influenced by the nutrient density of the diet and the level of energy requirement of the pig, which may be affected by previous nutritional history.

Means, standard deviations and phenotypic correlations among 28 performance and carcass variables are reported on 1042 barrows and gilts of two breeds selected at random from pigs tested by the Pig Industry Development Authority. In addition, multiple regressions predicting the lean content of the carcasses and some relationships between visual scores and other carcass variables are presented. The lean content of any one of four joints gave better estimates of overall leanness than the best combination of other measurements—that involving C, K and eye-muscle area.

Haemoglobin (Hb) and transferrin (Tf) types have been studied in the breeds Muturu, N'Dama, Gudali and Red Bororo of Nigeria, West Africa.

The Hb gene frequencies were: Muturu, HbA = 0·72, HbD = 0·28; Gudali, HbA = 0·60, HbB = 0·32, HbC = 0·08; Red Bororo, HbA = 0·54, HbB = 0·44, HbC = 0·02.

Transferrin studies showed six different Tf phenotypes in Muturu their distribution being in agreement with the occurrence of the alleles TfA, TfD1 and TfD2. In N'Dama nine different Tf phenotypes were observed and were explained by the alleles TfA, TfD1, TfD2 and TfE. In Gudali 15 different Tf phenotypes were found with a distribution in agreement with the occurrence of the alleles TfA, TfB, TfD1, TfD2, TfF and TfE. All alleles in this breed occurred at frequencies above 0.1. In a limited number of Red Bororo cattle nine Tf phenotypes were seen. Their distribution can be explained by the occurrence of the six genes: TfA, TfB, TfD1, TfD2, TfF and TfE.

One hundred and forty-four Large White weaner pigs were used in each of two experiments to investigate the nutritive value of liquid separated milk. Two experimental diets, one based on separated milk and barley meal, the other on separated milk, soya bean meal and barley meal were compared with control meals of the type used in the Pig Industry Development Authority's progeny testing stations. The amounts of milk in the experimental diets were adjusted so that the lysine concentrations in the dietary dry matter were similar to those of the control meals. All diets were given according to a restricted scale relating daily dry matter allowance to live weight, to a scale relating digestible energy allowance to live weight and to ‘appetite’. In the first experiment, pigs were slaughtered at 200 lb live weight, in the second at 260 lb live weight.

Pigs given the separated milk and barley meal diet performed similarly to those given the control meals; those given the separated milk, soya bean meal and barley meal diet had better feed conversion efficiencies than control pigs, particularly over the range 200 to 260 lb live weight. Pigs given diets containing milk had higher killing-out percentages and shorter carcasses than those given the control meals. Diet had no statistically significant effect on the percentages of fat and lean in the sides.

The effects of plane of nutrition were demonstrated by the faster rate of gain and poorer carcass quality of pigs fed to ‘appetite’.

It was concluded that the nutritive value of separated milk is explained by its high energy and lysine content. There was no evidence of any unknown beneficial factor in it.

1. A direct calorimeter is described, capable of partitioning the total heat loss from individual pigs into its evaporative and non-evaporative components; tests revealed that the instrument measured non-evaporative heat loss with a coefficient of variation of 3%, and evaporative heat loss with a coefficient of variation of 5·0% at 10° and 20°C, and 5·6% at 30°C.

2. Experiments were carried out to measure the differences between heat losses at 20° and 9°C, or at 20° and 30°C, for pigs weighing approximately 26 kg and 64 kg; each measurement lasted 20 minutes and was made after an equilibration period of 3–4 hr.

3. Heat loss was proportional to body weight raised to the power of 0·6, under the present experimental conditions, over the range 26–64 kg at 20°C.

4. Total heat loss at 9°C was significantly greater than at 20°C for pigs of both sizes; total heat loss at 30°C was smaller than at 20°C for pigs of both sizes, the decrease being significant for the heavier pigs only. Nonevaporative heat loss increased significantly with decrease in temperature. Evaporative heat loss at 30°C was significantly greater than at 20°C. The increases in total and non-evaporative heat losses at 9°C when compared with 20°C, were significantly greater for the lighter pigs than for the heavier pigs. The small decrease in total heat loss at 30°C, compared with 20°C, may have been due to non-attainment of thermal equilibrium at 30°C.

5. Values for whole body thermal conductance were calculated from the measurements of non-evaporative heat loss, and these indicated that a change in tissue conductance took place between 20° and 30°C; the mean values at 9°C were 3·78 and 3·15 kcal/°C.m2.hr for the lighter and heavier pigs respectively.

6. Evaporative heat loss at 20°C amounted to 280 and 330 kcal/m2. 24. hr for the lighter and heavier pigs respectively. This component of heat loss amounted to 8% and 13% of the total heat loss at 9° and 20°C respectively for all pigs; the corresponding values at 30°C were 32% and 25% for the lighter and heavier pigs respectively. The increased evaporative loss at 30°C was accompanied by an increase in respiratory rate.

7. These results agreed well with the results of previous work with groups of pigs, for heat loss at 20°C. Comparisons with that work indicate that the increase in heat loss at 9°C, when compared with 20°C, was greater for individual pigs than for groups of pigs, of both sizes.

A sib selection programme for length of carcass was carried out for five generations within a closed herd of Large White pigs. A generation interval of one year was obtained.

Litter production was good throughout the project and the numbers of pigs born and reared in the final generation were 11·2 and 10·3 respectively.

Overall response to selection was predicted with reasonable success. The increase in length was associated with an increase in number of vertebrae.

Heritability for length of carcass computed from the pooled components of variance was 0·53 ± 0·12. Realized heritability was 0·5 ± 0·1. No control strain was maintained.

Correlated traits moved in the expected directions and responses were beneficial for traits such as backfat measurements and chest depth, but unfavourable for belly thickness and ham conformation. Carcass acceptability was not good initially and this deteriorated during the project. The difficulties involved in maintaining selection pressure and herd size are discussed. Abnormalities and lameness were recorded and did not increase systematically over the experiment.

It is suggested that the specific relationships between ‘conformation’, carcass value and viability require further investigation with particular reference to length of leg and length of carcass.

Relationships were measured between growth constants for live weight and tissue weights in the hind limb sample joint in 60 Suffolk × Welsh lambs.

The lambs were random samples of five male and five female from the single-born progeny of each of six Suffolk rams. They were slaughtered as near to 75 lb live weight as possible and a standard cut of the hind limb, extending up to and including the muscles of the upper thigh and pelvis, was removed from the carcass for dissection.

Whilst muscles in the upper thigh, pelvis and abdomen were affected predominantly by sex, sire effects increased and progressively substituted them in passing down the limb.

Linear growth in body weight was positively associated with weight of bone and muscle in the sample joint but not with subcutaneous or intermuscu-lar fat.

Closely shorn Scottish Blackface female sheep aged 9–14 months, half on high plane and half on low plane nutrition, were subjected, in climate chambers, to two short acute cold exposures down to −20°C. The acute exposures were separated by two weeks chronic exposure to a moderately subcriticai temperature (+8°C) or to a thermoneutral temperature (+30°C). Most of the sheep showed a greater resistance to body cooling at the second acute exposure (Slee and Sykes, 1967). This increased resistance to hypothermia, defined as acclimatization, was apparently influenced more by acute than by chronic cold exposure. The present paper deals with changes in skin temperature, heart rate, shivering intensity and skinfold thickness which also resulted from cold exposure, and accompanied acclimatization.

After acute cold exposure followed by chronic exposure to +8°C the following changes in these parameters were observed:

1. Extremity skin temperatures and heart rates were consistently increased at thermoneutral ambient temperatures.

2. Vasoconstriction of the extremities and increased heart rate, both of which normally occur during the early stages of cold exposure, were delayed.

3. Heart rates at sub-zero ambient temperatures were increased.

4. Cold-induced vasodilatation at sub-zero ambient temperatures was increased.

After acute cold treatment alone the intensity of shivering during the second acute exposure was reduced. Also the onset of foot vasoconstriction was slightly delayed.

A highly significant relationship was observed between shivering intensity and heart rate during cold exposure.

Plane of nutrition had less effect on the physiological responses to cooling than did previous cold experience.

It was suggested in discussion that the physiological responses associated with acclimatization were: elevated basal metabolic rate, delayed onset of vasoconstriction and delayed metabolic response to cold, and consequent lowering of the critical temperature. Summit metabolism was also increased and shivering intensity reduced during acute cold exposure. Some of these responses could have resulted from either acute or chronic moderate cold exposure. However their persistence, once induced, appeared to depend upon continued exposure to moderate cold.

1. Two growth trials and digestibility trials were carried out with 54 steers given diets containing either 11%, 14% or 17% crude protein in the dry matter and the same concentration of metabolisable energy.

2. There were no significant differences in either dry-matter intake or live-weight gain by the steers given the diets containing 14% or 17% crude protein. Dry-matter intake was lower for the steers given the diet containing 11% crude protein and their live-weight gain was lower up to 250 kg live weight. Beyond 250 kg live weight their live-weight gain was similar to that of the steers on the two other treatments.

3. Both dry-matter digestibility and apparent nitrogen digestibility were lowest for those steers given the diet containing 11% crude protein.

1. The voluntary dry-matter and water intakes of indigenous and exotic cattle on high plane rations have been compared under similar conditions of management.

2. At similar live weights, exotic cattle have a much higher feed intake relative to maintenance than indigenous cattle.

3. Water intake was closely related to dry-matter intake, irrespective of live weight, and varied only very slightly between the two types of cattle.

4. Exotic cattle were more than twice as efficient as indigenous cattle in converting feed into live-weight gain. It is suggested that this is largely a reflection of the increased feed intake, relative to maintenance requirements.

5. Stage of maturity, degree of fatness and their relation to conversion efficiency are discussed.

1. Scottish Blackface and Tasmanian Merino one-year-old males were exposed to cold in climate chambers. The environmental temperature fell slowly from +10°C to −15°C in the first experiment when the sheep were in full fleece and from +30°C to −5°C in the second experiment when the same sheep were closely shorn. In the second experiment each sheep received two identical exposures separated by one day spent in a cool environment. Rectal temperatures and skin temperatures on the body and the extremities were recorded.

2. In experiment 1 skin temperatures on the feet and ears generally fell sharply due to vasoconstriction, especially in the Blackface sheep. The Blackface sheep showed earlier and more intense vasoconstriction than the Merinos.

3. In experiment 2 foot and ear skin temperatures fell smoothly with gradual vasoconstriction. In contrast to experiment 1, both breeds were similar in the time of onset of vasoconstriction. Foot temperatures, however, were significantly higher and vasoconstriction correspondingly later during the second exposure of experiment 2 than during the first exposure.

4. The skin temperature at which vasoconstriction occurred remained similar irrespective of breed, shearing or exposure occasion. But the ambient temperature at vasoconstriction was significantly influenced by all these variables.

5. Cold-induced vasodilatations were more frequent in experiment 1 than in experiment 2.

6. Retarded vasoconstriction among the Merinos in experiment 1 could, except for two sheep, be accounted for by their superior fleece cover. In experiment 2, the delayed foot vasoconstriction on second exposure was attributed to increased blood flow resulting from acclimatization.

1. Four groups of three litter-sister Large White gilts were given during four successive pregnancies a daily meal allowance of either 2·70 kg (High), 1·35 (Low) or 1·35 kg for 76 days followed by 2·70 kg until parturition (Low-High). During 8-week lactation periods all received the same daily allowance of 1·8 kg meal plus 0·35 kg for each piglet suckled.

2. On the 100th day of the fourth pregnancy all sows were slaughtered. The major internal organs were weighed and measurements recorded of the length of carcass and backfat thickness at shoulder, midback and loin. The carcasses were then separated into bone, skin, subcutaneous fat and muscles plus intermuscular fat. The weights of radius-ulna, tibia-fibula, humerus and femur were recorded.

3. In each of the treatment groups the live-weight changes of the sows in the fourth pregnancy were almost identical to those in the third pregnancy.

4. The mean total carcass weights for the High, Low and Low-High sows were 154, 92 and 110 kg respectively, and the mean subcutaneous fat contents of the carcasses 14, 4 and 6 kg respectively.

5. The relative proportions of the weights of the organs to carcass weight, weight of bone to weight of muscle plus intermuscular fat, and the weight of individual bones to total bone weight were relatively unaffected by the treatments after allowance had been made for total carcass weight.

6. The implications of the changes in body composition on the lifetime reproductive performance of sows are discussed.

The relationship between mature weights of domestic species and the times they take to mature in live weight is extended to breeds and strains within a species and to sex differences within a breed or strain. Results based on the Gompertz growth curve are found to be essentially the same as those based on Brody's growth curve. Both confirm the relationship of proportionality between the time a species takes to mature in live weight and its mature weight raised to the power 0·27 or some power close to this. The overall weighted average coefficient was 0·273 ± 0·029 for Brody's (1945) growth curve data and 0·276 ± 0·030 for the Gompertz growth curve data of Laird (1966). The weighted average coefficients of 0·358 ± 0·098 for strains within a species and 0·343 ± 0·049 for sexes within a strain, although not significantly greater than 0·27, suggest that a coefficient of ⅓ might be a better value to adopt when the relationship is confined within species.

Birds as a class matured significantly more rapidly than expected from their mature weight and mammals significantly more slowly. Body temperature could account for this class difference in maturing time but not for deviations of individual species or strains. Relative to their mature weight, some species appeared to take much less time to mature than others, with possibly a 2- to 3-fold genetic difference between extremes of the range.

The main use of the relationship obtained lies in providing a ‘metabolic’ age scale on which animals or species can be examined for differences in immature physiological characteristics such as maturing time, body composition or efficiency of food utilization independently of differences in adult size.

1. Four growth trials were carried out with 297 group-fed steers given diets based on barley, minerals and vitamins, unsupplemented or supplemented with either soya bean meal or various sources of non-protein nitrogen.

2. Steers given unsupplemented barley (11% crude protein in dry matter) had inferior growth rates up to 300 kg live weight but thereafter were equal to those given barley supplemented with urea in the drinking water or soya bean meal.

3. There were no significant differences in the growth rates of steers given barley supplemented with soya bean meal and those given barley supplemented with ammonium and mineral salts of formic acid or a mixture of acids (predominantly acetic).

4. In two out of three trials, tenth-rib joints from steers given barley supplemented with ammonium salts of mixed acids contained less fat and more protein and water than those from steers given barley supplemented with soya bean meal or proprietary protein supplements.

5. A number of possible explanations for the apparent carcass differences is discussed.

Live weight of 180 free-grazing Blackface ewes was measured approxim-ately every two weeks throughout a 12-month period. Mean live weight was at a maximum (47 kg) in late autumn prior to mating and declined progressively to 39 kg at about the time of parturition.

Six ewes were slaughtered in November before mating, six at about the 16th week of pregnancy, and a further 11 in April during the final week of pregnancy. The loss of weight of maternal tissues (i.e. live weight less the weight of fleece and contents of the gastrointestinal tract and gravid uterus) during this period was more than 20% (7·5 kg) and comprised 51% of the fat, 14% of the water, and 20% of the protein plus ash present at maximum live weight. During the earlier stages of pregnancy there was an appreciable loss of water from the maternal tissues, but in late pregnancy the rate of water loss decreased and that of fat increased considerably.

The distribution of fat throughout the maternal tissues at different levels of total fat content and the pattern of fat mobilization from various depots are described. The largest single contribution to fat loss during the pregnancy period was that of the subcutaneous reserves, which were depleted by 86%, most of this being lost during the first four months. At the other end of the scale bone fat reserves were reduced by only 25%, almost all of this occurring during the final month.

Carcasses of 156 pigs (78 gilts, 78 barrows) slaughtered at 200 lb live weight, were probed by introscope at six positions in line with the last rib. Backfat was measured directly and muscle depth was obtained as the difference between total probed depth from skin to rib and backfat depth. The various measurements were used to predict eye-muscle area measured on the exposed cross-section of the longissimus dorsi cut at the level of the last rib.

Depth of muscle at 7·5 cm and depth of fat at 10 cm were the best predictive measurements for both barrows and gilts, although muscle at 4·5 cm in gilts and at 10 cm in barrows were of equivalent value to muscle at 7·5 cm. The correlation between observed and predicted values of eye-muscle area was 0·8. The accuracy of these predictions compared favourably with those of carcass lean percentage from maximum depth of backfat at shoulder, minimum depth of fat at loin and fat depth at ‘C’.

Two alfalfa varieties and four grass species were harvested for hay at several stages of maturity. Each hay was given to sheep to provide measures of voluntary consumption and digestibility. Digesta samples were obtained from the reticulo-rumen, omasum and abomasum by killing the sheep at the end of the feeding periods.

Sieving analyses of the digesta revealed that the fraction retained by a 0·25-mm sieve provided greater differentiation between experimental treatments than those retained by 0·5-, 1·0- or 2·0-mm sieves. The weight percentage of this fraction was used as a measure of the relative particle size despite its profound dependence on size, shape, density and distribution of individual particles.

The variation in relative particle size of digesta from different sheep fed on the same diet was illustrated by coefficients of variation ranging from 4 to 11%. Four replicates, however, were sufficient to detect numerous differences (P<0·05) between experimental treatments.

Omasal digesta from alfalfa hay had a greater relative particle size than those from the grass hays at comparablematuritystages. This may be attributable to an apparently more compact particle shape observed in the alfalfa digesta, assuming that in a simple physical sieving process the most compact particle passing a given opening will have the greatest mass. It was proposed that digesta particle shape may have greater specific importance than relative particle size for the rate of passage and voluntary intake of coarse roughage.

A direct relationship was observed between voluntary feed consumption and the relative particle size of omasal digesta from different grass hays at similar maturity stages. This was the reverse of that observed between different maturity stages within hay species. It was hypothesized that the former relationship was due mainly to changing mass of the individual particles passing the reticulo-omasal opening, whereas the latter relationship was caused mainly by the particle size distribution.

The relationship between the relative particle size of digesta from the reticulo-rumen and that of digesta from the omasum supports the theory that the reticulo-omasal opening is the site of major obstruction for the passage of coarse roughage through the digestive system of ruminants.

Chemical and physical compositions were respectively determined on right and left sides of 23 Scottish Blackface ewe carcasses. Relationships were derived whereby physical carcass composition, in terms of muscular tissue plus associated fatty tissue, subcutaneous plus perirenal fatty tissues, and bone, could be estimated from weights of chemically determined water, fat, ash, and fat-free dry matter. The use of these relationships is discussed, and it is suggested that in certain circumstances the estimation of physical carcass composition from chemically determined components could result in considerable economies of time and labour.

The use of certain readily determined physical components as indices of the chemical composition of the whole body is considered, and relevant prediction equations presented.

Twenty-two Ayrshire twin female cattle were kept for up to seven years of age on six equally spaced levels of constant food intake, ranging from 35 to 140 lb per week of a complete pelleted diet. Analysis was confined to the period between 5 and 7 years when growth had practically ceased and equilibrium maintenance requirements could be determined.

Equilibrium weight maintained was directly proportional to the level of constant food intake.

This relationship obtained by controlling food intake was significantly different from the 0·73 power relationship that applies across species. In establishing the present relationship, systematic genetic differences were excluded, and this is probably the main condition required for weight eventually maintained to be proportional to food intake. In contrast, the well-established proportionality of food intake to metabolic weight is essentially based on a species comparison and is thus due almost entirely to genetic differences.

A mathematical model is given which combines (1) the genetic relationship of proportionality of voluntary food intake to mature metabolic weight and (2) the nutritional relationship of proportionality of equilibrium weight maintained to level of constant food intake. The model is then used to partition variation into systematic and random components.

The experiment provides some indication of the extent of individual variation in efficiency of maintenance within breeds, the amount which is genetic, and the repeatability of this efficiency from age to age. Some information is also provided on variation in voluntary food intake, mature weight maintained and efficiency of maintenance on ad libitum feeding.

Methods of estimating efficiency of maintenance using ‘feed and weigh’ techniques, selection for efficiency of maintenance, the correlated response in mature weight, and selection for relative food capacity are briefly discussed.

In three trials, two with suckler cows and one with lambs, supplementary forms of dietary nitrogen and/or energy were added to a basal diet of barley straw offered ad libitum. The nitrogenous supplements appeared to have a small effect on the intake of straw but only when they were available for frequent consumption. The addition of cereals to the diet did not affect the intake or digestibility of the straw but reduced the live-weight losses.