The last 10 years have seen a significant expansion in the scope of attempts to manipulate the growth of animals (Buttery, Lindsay and Haynes, 1986). The expansion of interest has been driven by a number of factors, both economic and theoretical. At the economic level the need to develop energetically and economically efficient strategies of animal production has been coupled with a renewed awareness of the implications for human health of excessive intakes of saturated fats. Emphasis then has switched from the maximization of weight gain as an end in itself towards a need to promote protein deposition at any given intake and, at the same time, to reduce the fat content of meat and meat products. These twin objectives might be achieved by one of three strategies: the promotion of protein deposition alone, because at any given rate of weight gain this will tend to minimize the rate of fat deposition (the so-called repartitioning effect); the reduction of fat gain (an approach that has received particularly close attention by those concerned primarily with human obesity); or ideally the simultaneous promotion of protein accretion and depression of that of fat.

Milk production, reproduction, blood composition and health were studied in two groups of British Friesian cows given food either twice daily in the parlour (IPF group) or through automatic out-of- parlour food dispensers (OOPF group) in the first 14 weeks of two consecutive lactations. The numbers of cows in the IPF and OOPF groups were 28 and 29 respectively in year 1 and 40 and 35 in year 2.

There were no differences in milk production or reproduction in year 1 but in year 2 the OOPF group had significant proportional increases in the yield of fat (+0·079) and protein (+0·072) and the median time from calving to conception was reduced by 43·5 days. In the IPF group body condition score was lower than in the OOPF group in year 1 (2·27 v. 2·59; P < 0·001) and in year 2 (2·37 v. 2·57; P < 0·01); as were serum total protein (75·8 v. 77·5 g/l; P < 0·05) and (73·9 v. 75·8 g/l; P < 0·01) and plasma glucose concentration (215 v. 2·32 mmol/1; P < 0·001) (2·28 v. 2·42 mmol/l; P < 0·01). In year 2 only, serum urea was lower (5·52 v. 6·07 mmol/l; P < 0·001) and serum copper higher (131 v. 11·9 μmol/l; P < 0·001) in the IPF group; the activities of aspartate amino transferase (1·66 v. 1·62 logm i.u. per 1; P < 0·05) and of glutamate dehydrogenase (1·00 v. 0·70 logm i.u. per 1; P < 0·001) were higher, despite no significant difference in fat deposition in the liver. The only significant difference in the incidence of disease was fewer cases of mastitis in the OOPF group in the second year (21 v. 12 cases).

The similarity in concentrate intakes, together with higher concentrations of blood glucose and total protein and better condition score, indicate either a more efficient utilization of energy in the OOPF group or a lower consumption of forage in the IPF group. The increased activities of liver enzymes and the high serum copper coupled with the increased incidence of mastitis and poorer fertility may indicate the release of endotoxin following chronic lactic acidosis in the IPF group.

This study involved two groups of calves, one group consisted of eight Angus × (Friesian × Hereford) calves born in the late summer and kept with their dams in the field. The other group consisted of 20 autumn-born Friesian calves kept indoors in individual stalls. Similar ethograms and techniques were used to study their behaviour up to 8 weeks of age, thus allowing comparisons to be made of the proportion of time spent in various activities, as well as changes in the sequences of behaviour with age. In general, the activity of the calves of both groups showed a similar trend in development. However, the field calves spent significantly more time in investigatory behaviour while the confined calves showed a significantly higher frequency of investigatory behaviour and indulged in more self grooming. The analysis of behavioural sequences showed few differences in focal points or direction of transitions from one behavioural pattern to another, suggesting that the integration of activities into developing motor patterns in the calf is determined ontogenetically with little modification by the environmental factors encountered in this study. However, the confined calves showed a greater mean number of transitions per hour. The findings are discussed in relation to the welfare of the confined calf.

A sward of perennial ryegrass was either directly ensiled at 181 g dry matter (DM) per kg fresh weight with formic acid applied at 3·6 1/t fresh material or wilted for 65 h to achieve a DM concentration of 407 g DM per kg. Physical and respiration loss were measured in the field and losses during ensiling were estimated from buried bags. The silages were offered to 58 British Friesian steers, initially 3 months of age and 101 kg live weight (LW). Ten steers were allocated to an initial slaughter group and the remainder were offered the two silages either ad libitum or at two restricted levels of feeding. These animals were slaughtered after a mean period of 112 days to estimate the increments in the components of the body.

Loss of DM in the field increased from 4·3 to 86·6 g/kg on wilting and proportionately 0·75 of this additional loss was due to respiration. The fermentation characteristics of the silages were broadly similar except that the concentration of ethanol was higher in the unwilted than in the wilted silage (57·6 v. 5·6 g/kg DM). Losses of DM during ensiling were slightly higher with the unwilted (104·4 g/kg ensiled) than with the wilted (80·1 g/kg) material. Losses of nitrogen were relatively higher and energy losses lower than was the loss of DM.

Wilting significantly depressed the digestibility of gross energy from 0·651 to 0·631 (P < 0·001) and at the ad libitum level steers ate proportionately 006 more wilted silage (P > 0·05) resulting in similar intakes of digestible energy. At the ad libitum level of feeding steers given wilted silage gained more LW (+55 g/day) and empty-body weight (+64 g/day) than those given unwilted silage (P < 0·05). However, steers given wilted silage contained less fat and energy in the empty body at slaughter than those given unwilted silage. Thus, wilting did not influence the efficiency of utilization of digestible energy for energy retention nor the efficiency of utilization of dietary protein for protein gain. Since efficiencies by the animal were similar and also the increased field loss on wilting was partly compensated for by a reduced silo loss, it is concluded that the proportion of energy and protein in the standing crop retained by the steers is unaffected by wilting (65 and 64 kJ/MJ and 125 and 138 g/kg N for unwilted and wilted systems respectively). Further work is needed to establish the effect of wilting for a shorter period than in the current trial by increasing the drying rate of herbage.

Plasma progesterone concentrations were measured over two collection periods from two groups of mature non-pregnant cows involved in a twin-breeding experiment. One group (T) consisted of cows obtained from private herds after having produced at least two sets of twins each; the other was a control group of similar ages and breeds. Yearling heifers from the same breeding experiment were also included. The mean progesterone concentration from cows in the T group was proportionally 0·83 of the value in control cows and the cow group effects were consistent in direction for samples obtained after single or double ovulations. Results were also consistent in early oestrous cycle (days 3 to 7, oestrus = day 0), mid cycle (days 8 to 13) but not late cycle (days 14 to 18). Concentrations were significantly higher in yearling heifers than in control cows. There was a trend for higher progesterone concentrations after double than after single ovulations assessed by rectal palpation, but differences were not significant.

The effects of winter shearing on the food intake and performance of housed ewes was studied in a series of three experiments. Winter shearing resulted in a proportional increase of dry-matter intake in ewes of 0·16 and 0·43 on two silage-based diets, of 0·09 on swede-based diets, but of only 0·02 on a hay-based diet. Shearing increased intake by a greater amount in smaller ewes and a similar trend occurred on diets containing a greater proportion of barley. Shearing increased average lamb birth weight by about 600 g (4·65 kg v. 4·06 kg), apparently as an effect of shearing per se rather than as a result of the increased energy intake. An increase in gestation length of around 1·8 days accounted for one-fifth of this increased birth weight. The effect on gestation length of shearing was to increase the unnaturally short gestation of housed unshorn ewes, this short gestation being attributed to problems of heat stress in late pregnancy. Results indicated management advantages of winter shearing in favourable climatic environments.

A study of the factors affecting weight in traditionally managed goats and sheep in central Mali was undertaken during 1978–84. Sheep were heavier than goats at all ages. Birth weights of goats (2·2 kg) were significantly affected by year and season of birth, parity, type of birth, sex and system (rain-fed millet or irrigated rice). Lamb birth weights (2·9 kg) were affected by all these sources of variation except year. System did not exert a significant influence on kid weights at 30 (4·3 kg), 90 (7·5 kg) or 150 days (10·5 kg) but the random effects of flocks and dams and the fixed effects of season, year, parity, type of birth, sex and the interaction of season × year were all significant at all three ages except for year at 30 days. Lamb weights (5·7, 11·1 and 15·5 kg) were significantly affected at all three ages by all sources of variation except season × year effects at 90 and 150 days. Repeatabilities of lamb weights were higher than of kids, probably due to milk being taken for human consumption from goats. There were few significant effects at post weaning to 730 days except those related to sex. Post-partum weights of goats (26·0 kg) were not affected by system, by the type of parturition nor by the sex of the young but were affected by season and year of parturition and by parity. Ewe post-partum weights (30·6 kg) were affected only by system and parity. Changes in weight over the year, pooled for 7 years, in specific age and sex groups averaged proportionately about 005 above and below the annual mean. Weights of mature animals were about 0·05 lower in 1984 than in 1978. Seasonal and long-term effects on weight are much less marked in small ruminants than in cattle under the same management system in the central Mali environment and the allocation of future research effort should take into consideration the relative advantages of the two types of stock.

Thirty-two kid goats of the Granadina breed were used in four trials of three factors: milk type (goat milk and milk replacer), intake level (1·86 and 2·48 maintenance) and slaughter age (15, 30, 45 and 60 days). Weaning was carried out between the 31st and 45th days. The composition of the carcass and its different cuts and the development of the stomach compartments were studied.

Both the high intake level and use of goat milk produced a statistically greater fat proportion in the carcass. At 30 days of age in kids given goat milk at the high intake level the fat proportion of the carcass was 130 g/kg. The variations in bone proportions were inverse to those for fat. The muscle proportions were affected by age, overall. The tissue composition of the different cuts showed similar responses to those in the carcass. The stomach compartments were affected most by age.

The results show that kids of the Granadina breed have a good fattening capacity. The feeding and weaning system used here produced kids by 60 days of age with stomach compartments similar in proportion to those of adult goats.

Genetic size-scaling accounts for most of the variation found among mammalian species in food intake and growth rate, with food conversion efficiency independent of the body size of the species. Is the same true of breeds and strains within species?

Animals from Soay, Welsh Mountain, Southdown, Finish Landrace, Jacob, Wiltshire Horn and Oxford Down sheep breeds and from a breed of feral goats were grown to 0·40, 0·52, 0·64 or 0·76 of the mean mature weight of their breed and sex. Food was offered ad libitum and individually recorded.

Allometric growth coefficients were obtained for fleece weight, femur weight and femur length. Fleece was late maturing and femur early.

Breed and sex size-scaling coefficients, obtained by regression of breed and sex means on mature size, were similar to those found at the species level for age from conception to slaughter, time taken to mature and food conversion efficiency. Coefficients were higher than expected for total and daily food consumption, especially at early stages of maturity. Most breed coefficients were close to expectation while sex coefficients were somewhat higher than expected.

There were significant breed deviations: Welsh Mountain, Oxford Down and probably Soay sheep required less time and Jacob sheep and feral goats required more time to mature than expected from differences in mature size. Soay and Welsh Mountain sheep appeared to be more efficient and feral goats and Jacob sheep less efficient food converters over the same maturity interval.

Animals from Soay, Welsh Mountain, Southdown, Finnish Landrace, Jacob, Wiltshire Horn and Oxford Down sheep breeds and a breed of feral goats were slaughtered when 0·40, 0·52, 0·64 or 0·76 of mature body weight. The effects of stage of maturity, breed and sex were examined in the following traits: gut content as a proportion of slaughter weight; blood, omental plus mesenteric fat, perirenal fat, alimentary tract, ‘remainder’ of non-carcass parts and hot carcass, each as a proportion of fleece-free empty body weight; also shoulder, rib, loin and gigot joints and their commercially higher-valued (prime) and lower-valued cuts, each as a proportion of carcass weight.

As a proportion, gut content declined as animals matured, as also did blood, alimentary tract, ‘remainder’, prime shoulder, shank and prime gigot. Increasing proportions were internal fat depots, the hot carcass, rib, loin and gigot flank. Males accumulated significantly less internal fat and more shoulder than females.

When equally mature in live weight, males had proportions that were significantly lower for perirenal fat, rib and gigot and higher for shoulder and pelt plus head, feet and organs.

There were significant inter-breed regressions on mature body weight. The proportion of blood, alimentary tract, pelt plus head, feet and organs, and prime gigot declined with breed size, while hot carcass, brisket, rib and loin proportions increased. These regressions were attributed to a non-random sample of breeds. The small Soay breed had proportions of internal fat and hot carcass which were well below average, and higher proportions of blood, alimentary tract and ‘remainder’. Soay sheep also had a higher proportion of commercially higher-valued cuts in the carcass. In contrast, the large Oxford Down breed had low proportions of non-carcass components (except alimentary tract) and high proportions of lower-priced cuts and prime rib. Feral goats had a greater, and Southdown sheep a smaller, proportion of gut content than other breeds.

Males and females from Soay, Welsh Mountain, Southdown, Finnish Landrace, Jacob, Wiltshire Horn and Oxford Down sheep breeds and a breed of feral goats were slaughtered when they reached 0·40, 0·52, 0·64 or 0·76 of the mean mature body weight of their breed and sex. Total weight of dissected muscle was close to 0·30 times fleece-free empty body weight, or 0·24 times live weight, for all breeds and stages of maturity. The growth of 12 individual muscles or muscle groups dissected from the commercially higher-valued joints of the carcass, was examined in relation to live weight and total muscle weight. Limb muscles matured early. All 12 muscles, when combined, also matured early so that the proportion of lean tissue from the higher-valued joints declined as live weight increased.

There were small but significant sex differences in the relative growth rate of some muscles. The abdominal muscles were early maturing for males and average for females. There were also sex differences in muscle weight distribution. The proportion of muscle in the hind limb of females was 1·055 times that in males, while the 12 muscles from higher-valued cuts constituted 0·403 of total carcass muscle for females and 0·389 for males, a proportional difference of 0·035.

Muscle weight distribution was unrelated to breed size with the possible exception of m. gastrocnemius which appeared to be relatively smaller in genetically larger breeds. After accounting for differences in mature weight, there remained small but significant breed deviations in muscle weight distribution. Southdowns had the most attractive distribution. Feral goats and Jacob sheep, although they had the highest proportion of total muscle, had a much less attractive distribution.

Three hundred and sixty male and female Californian ♂ × New Zealand White ♀ growing rabbits were used to study the influence of nine types of fat at 30 or 60 g/kg diet on growth and apparent digestibility. The fats used were: beef tallow (T), pork lard (L), sunflower oil (SO), two by-products from the oil-refining industry, sunflower oleins (O) and soya-bean lecithin (S), and 2: 1 (w/w) mixtures of T + S, L + S, O + S and T + O. All diets, including a diet without added fat, were formulated to a 190 g/kg acid-detergent fibre (ADF) level and to a 100 kJ digestible energy per g digestible protein ratio.

As O level in the diet increased, growth was significantly impaired (P < 0·001) but the other fats had no significant effect on this variable (P > 0·05). A maximum oleins concentration in the diet of 10 g/kg is suggested. Excluding diets with more than 10 g oleins per kg, a significant improvement in food conversion ratio was recorded for diets containing 60 g added fat per kg (P < 0·05). This improvement was related not only to a higher gross energy concentration of added-fat diets but also to a significantly (P < 0·001) higher energy digestibility (0·653 v. 0·602 for 60 g/kg added-fat diets and control diet respectively). Fat addition both at 60 and 30 g/kg also improved significantly (P < 0·001) dry matter, organic matter, crude protein and ether extract (EED) digestibilities. As a result, the use of ether extract in addition to ADF for estimating the energy value of diets including added fat, is proposed.

An increase in the degree of unsaturation of dietary ether extract increased significantly EED (P < 0·001), but did not affect other variables studied.

Dromedary camels (Camelus dromedarius) inhabit and are well suited to semi-arid and arid areas of north Africa, south-east Asia and India. Little attention has been given to their husbandry although they are an important livestock species in some areas. One of the limiting factors in camel production is the 2- to 3-year interval between calvings. In this study, three female calves (birth weight 32·5 kg) were weaned onto artificial milk 30 days after birth and the she-camels (400 to 500 kg) were mated 10 to 14 days later. Between 30 and 120 days of age the calves received mainly artificial milk and between days 120 and 180 they received concentrates and lucerne hay. While the calves sucked milk, intake averaged 6·9 l/day, metabolizable energy intake (MEI) averaged 19·5 MJ/day and average daily gain (ADG) was 0·87 kg. Ratios of conversion of milk intake (l/day) and MEI (MJ/day) to body-mass gain (kg/day) were 8·0: 1 and 22·4: 1, respectively, and to total body solids gain (kg/day) were 22·3: 1 and 62·7: 1, respectively. From days 30 to 120, ADG was 0·67 kg, and from days 120 to 180 ADG was 0·61 kg. The calves averaged 155 kg at 180 days and ADG to that age was 0·68 kg. All three she-camels conceived 10 to 14 days post weaning.

This study demonstrated that camel calves can be weaned early and that high growth rates can be achieved. In addition, she-camels can be mated shortly after parturition so that calving intervals can be reduced to 15 months.

In meat animals there is some interest in lean growth rate or lean food conversion efficiency as selection criteria. These traits may be estimated as the product of growth rate (or efficiency), killing-out proportion and carcass lean proportion. When used as selection criteria these product traits do not require estimates of genetic parameters or economic values for component traits. Hence, they may be more stable, and of longer-term use than classical economic selection indices. The purpose of this study is to compare expected responses to selection on product traits with expected responses from selection, either on individual component traits, or on an economic selection index. Formulae were derived for predicting the phenotypic and genetic correlations between a product and one component, and for predicting the heritability of the product trait; these depend on the coefficients of variation and heritabilities of components, and on the genetic correlations among them. When the coefficient of variation of one component is much higher than that of the other, (× 3), this component will tend to dominate the product trait. In cattle and sheep, and to a lesser extent in pigs, killing-out proportion and leanness are usually less variable than growth rate or efficiency. Thus, in many cases, there is little loss in response in lean growth (or lean efficiency) from selection solely on growth rate (or efficiency) regardless of leanness. Although product traits do not require derivation of economic values, their component traits do have implied economic values. Often more appropriate weightings will be given to components by using an economic selection index, even when economic values and genetic parameters are not estimated precisely.

The ease with which cattle can be handled during routine husbandry operations is a major concern to producers. Ease of handling is difficult to define but includes the case with which cattle can be moved through yards, through a race or held in a crush or scales. Few studies have attempted to measure ‘ease of handling’ of animals. ‘Temperament scores’ of cattle of various breeds, sexes and ages based on the scoring system originally described by Tulloh (1961) were recorded by Hearnshaw, Barlow and Want (1979). These scores were highly repeatable between scorers and within animals although some decline in scores occurred with repeated measurements. Hearnshaw et al. (1979) suggested that the scores were a measurement of ease of handling rather than temperament.

The forage: concentrate ratio in the diet is known to influence the fermentation characteristics in the rumen (Sudweeks, Ely, Mertens and Sisk, 1981). Increasing the proportion of concentrates in rations fed to dairy cows has been shown to narrow the acetate plus butyrate: propionate ratio in the rumen (Sutton, 1981) with an associated depression in milk fat concentration (Ørskov, Reid and McDonald, 1981). The magnitude of the effect, on milk yield and composition, of increasing the concentrate proportion in the ration has been shown to be dependent on feeding level (Sutton, 1981), and the number of meals of concentrate per day (Johnson, 1979) and also may be influenced by dietary protein level and source (Ørskov et al., 1981).