Data were available on crossbred meat lambs for 10 live-weight and growth traits (2585 lambs), 5 carcass traits (1884 lambs) and 10 dissection traits (944 lambs). These were the progeny born on an experimental farm over 5 years, from 102, 79 and 65 sires respectively for the three groups of traits. Genetic parameters were estimated from the sire components in a nested analysis of variance within breed of sire and year subclass, adjusting for sex, dam age, rearing type and other factors.

The heritabilities of the live-weight and growth traits were all low, the highest being average daily gain to slaughter (0·10, s.e. 0·06), and none was statistically significant. The heritabilities of the traits of carcass composition were much higher: percentage lean (0·41, s.e. 0·13), percentage fat (0·37, s.e. 0·13) and percentage bone (0·16, s.e. 0·10). Intermediate values were found for most other traits: killing-out percentage (0·16, s.e. 0·07), fat depth (0·21, s.e. 0·11), eye-muscle area (0·14, s.e. 0·10) and lean/bone ratio (0·13, s.e. 0·09).

Phenotypic and genetic correlations among the traits were also estimated. No major incompatibilities were found among the traits. The results are discussed in relation to the genetic improvement of lean meat production in sheep.

The half carcasses of 39 pre- and postnatal Romney sheep were dissected into anatomical units of bone and, where possible, into 32 muscle units which comprised nine functional groups. The growth of wet weight of the total bone and of the muscle groups (and their chemical components, which included deoxyribonucleic acid, protein, and total lipid) was compared with the growth of the carcass using allometric analysis.

Although bone grew faster prenatally than postnatally relative to carcass weight, the growth of total muscle and of all the muscle groups and their chemical components occurred at a constant, linear rate throughout the growth period studied.

The muscle: bone ratio decreased during prenatal growth, reached a minimum at around parturition and then increased postnatally.

The abdominal, m. longissimus and thigh muscle groups grew faster than total side muscle, relative to carcass weight.

Protein, and especially triglyceride, grew at relative rates which exceeded that of muscle wet weight.

The amount and proportion of intramuscular triglyceride, and the weights of the muscle groups in sheep at three different stages of growth, were predicted from allometric equations. The content of triglyceride was greatest in the cutaneous and neck muscle groups. As a proportion of total muscle, the thigh, m. longissimus and abdominal groups increased as carcass weight increased from 1 kg to 15 kg.

Two feeding trials were carried out with Israeli Friesian male calves, commencing at an average age of 7 to 10 days, and covering a suckling period of 30 days followed by a further 90 days. A conventional starter, or one that contained cotton hulls, was used. In each experiment one group of 10 animals served as a control and a similar group was monensin-supplemented. No coccidia were found in the animals. In experiments 1 and 2 monensin supplementation was associated with increased daily gains of 10% and 47% during the suckling period and of 6% and 17% during the next 90 days, but only the differences obtained in experiment 2 were significant. In both experiments, dry-matter intake relative to body weight was higher with monensin supplementation in period 1, but reduced in period 2. The effect of monensin on molar proportions of acetic and propionic acids was smaller than that reported by previous authors for older cattle.

A separate digestibility trial showed that monensin administered to suckling calves, either with milk replacer or directly into the rumen, improved dry-matter digestibility, increased the excretion of amylase, and tended to reduce that of trypsin and chymotrypsin.

Five ewes, with a wool depth of approximately 5 mm, were placed in a neutral (20 + 2°C) environmental temperature on day 139 of pregnancy, and five similar ewes were placed in a cold (0±2°C) temperature. They remained in these environments until their lambs were 8 days old. Samples of udder secretions, when present, and right-atrial blood were taken from the ewes at 12-h intervals.

Milk from ewes in the neutral environment had a high fat concentration for a brief period after parturition, before the full development of lactose secretion occurred.

In ewes exposed to the cold environment, plasma cortisol concentration was increased during the 2 days before parturition. Cold exposure had no effect on the onset of milk lactose secretion but increased the concentration of fatty acids in milk during the period −0·5 to +4·5 days relative to parturition.

Five hundred and seven British Friesian × Ayrshire bull calves were reared on a once-daily milk replacer feeding system from approximately 6 to 72 days of age in four naturally ventilated, unheated calf houses differing in design and degree of insulation. Environment within the calf houses was monitored each hour. Differences in design and degree of insulation produced small but significant differences in internal house temperature, humidity and air movement which had no measurable effect on calf daily live-weight gains.

Calves receiving 0·6 kg/day compared with 0·3 or 0·4 kg/day of milk replacer plus concentrates ad libitum ate less concentrates but had higher daily live-weight gains (0·56 compared with 0·49 kg/day respectively) (P < 0·001). Rations supplying similar amounts of metabolizable energy from varying proportions of milk:concentrate resulted in comparable live-weight gains. Results suggest that calf viability was affected by level of nutrition and that low levels of milk replacer feeding resulted in higher mortality. Naturally ventilated, unheated calf houses were demonstrated to be suitable for rearing calves in south-west Scotland.

Sheep of three pure breeds, the Scottish Blackface, South Country Cheviot and Welsh Mountain, and the crosses among these breeds, were inbred mostly by younger-parent offspring matings for three generations. Observations on lambs at 12 weeks of age were weight of fleece per unit area of skin, mean and variance of fibre length, both primary and secondary follicle density, and fibre diameter. The observations were analysed for the effects of inbreeding of the lamb and its dam, breed type, parity, and the sex and birth type of the lamb. Variation in the traits was also analysed for their relationship to lamb's live weight.

Secondary follicle density and the density ratio (Ns/Np) decreased with inbreeding of the lamb. Primary follicle density increased whilst secondary fibre diameter and mean fibre length decreased with inbreeding of the dam. The effects of inbreeding on the density ratio and on secondary fibre diameter were correlated with inbreeding effects on the lamb's 12-week live weight. For other traits inbreeding did not have a clear-cut effect. Heterosis observed in F2 lambs was in general greater than that previously recorded for F1. For mean fibre length and mean fibre diameter the comparison of the crossbred deviations from mid-parent of the F2 and inbred lambs suggested epistatic interactions were involved. The effect of inbreeding crossbreds and inbreeding purebreds was different for secondary follicle density and primary fibre diameter, the two traits most clearly exhibiting heterosis in the F2. Lambs from first parity ewes had finer primary fibres and lighter fleece samples than had lambs from later parities.

Total follicle density, primary follicle density, secondary follicle density, secondary/primary ratio and incidence of medullated fibres were studied in skin specimens from 78 2-year-old Merilin rams representing nine parent studs in Uruguay. The limited data available suggest that the studs sampled may fall into various groups, although separation into distinct groups is not equally well defined for all variables measured. Consequently, a firm conclusion about the Merilin awaits further information on fleece weight, staple length and body weight.

1. The primary growth of a tetraploid red clover was cut from 17 to 19 June and ensiled with formic acid at 3·81/t fresh crop (F), equal volumes of formic acid and formalin at 9 11/t (67 g formaldehyde per kg crude protein) (FF) or wilted and ensiled without additive (W). The silages were given ad libitum either alone or with supplements of dried grass or barley/fish meal at 6·7 g dry matter per kg live weight to 45 British Friesian male castrates, initially 3 months old and 104 kg live-weight.

2. The use of formaldehyde reduced the concentration of fermentation acids and of ammonia-nitrogen in the silage. Wilting the crop increased silage dry-matter content by 74g/kg fresh weight but this silage had the highest concentration of fermentation acids and of ammonia-nitrogen.

3. Digestibilities of diets containing silage FF were lower than those of diets containing silages F and W except when silage FF was supplemented with dried grass (interaction P <0·05).

4. The intake of silage W was on average higher than that of silages F and FF (P < 0·001). Supplements of barley/fish meal and dried grass depressed silage intake to a similar extent (P <0001). When silages were given as the sole feed, calves consuming silage F had higher live-weight gains than calves given silages FF and W (P <001). This effect was not apparent when silages were supplemented with barley/fish meal, but with a supplement of dried grass the calves given silage FF grew more slowly than those given silages F and W.

5. The results are discussed in relation to the possible effect of treatments on the supply of rumen-degradable protein and of amino acids to the animal.

Four experiments, each with 24 growing sheep, were carried out to investigate the effects of 8- or 16-h daylengths on growth and carcass characteristics. In the first two experiments, with 6- to 9-month-old castrated males, and 3- to 5-month-old female and castrated male animals, pair feeding of a concentrate feed was adopted. Live-weight gains were significantly greater under 16-h daylength, but carcass weights were not significantly increased because most of the live-weight difference was due to gut-fill. Carcass weights and measurements suggested that long daylength stimulated the growth of non-fat tissues at the expense of fat.

The third experiment compared castrated males fed either ad libitum or restricted to a daily ration proportional to each animal's own weight from 6 to 9 months of age. Food intake was higher in the ad libitum sheep but not significantly so. Weight gains were, however, significantly greater with ad libitum feeding and long daylength, compared with restricted feeding and short daylength, respectively. Gut-fill was greater in those kept in 16 h daylength and the small advantage in carcass weight was not significant. Carcass characteristics were not markedly affected by daylength, while carcass weight and fatness were higher following ad libitum feeding than restricted feeding.

In the fourth experiment 12 female sheep, aged 9 months, were individually rationed according to live weight and slaughtered after 4 weeks exposure to 16- or 8-h daylengths; another 12 were slaughtered after 7 weeks of treatment. Gut-fill was significantly greater in long daylength at both slaughter times, showing that the effect of daylength on gut fill has occurred within 4 weeks of the start of treatment, while live weight has not been observed to be affected at this stage in any experiment in this series.

Overall these experiments show little stimulating effect of long daylength on growth, and a large effect on gut-fill.

Two groups of ewes in good body condition at the start of the breeding season were given either sufficient feed to maintain their body weight or 500 g/kg of a maintenance ration such that they showed a continuous fall in body weight. On three separate occasions after introducing the nutritional regimens, all ewes were challenged on day 12 of the oestrous cycle with 150 μg luteinizing hormone-releasing hormone. Prolonged chronic undernutrition resulted in a significant increase in luteinizing hormone release in response to luteinizing hormone-releasing hormone injection (P < 0·05), whereas the mean pre-injection luteinizing hormone concentrations were significantly reduced by undernutrition (P < 0·01).

1. A primary growth of perennial ryegrass was cut on 8 to 11 May (early) or on 12 June (late) for comparison with the primary growth of a tetraploid red clover, which was cut either on 1 or 2 June (early) or on 28 June (late). The crops were ensiled, after wilting for about 4h, with the addition of formic acid at 2·21/t fresh crop. The silages were given ad libitum alone or with rolled barley at 11·5 g dry matter per kg live weight to 40 British Friesian steers initially 3 months old and 108 kg live weight.

2. On average there was no significant difference in digestibility between perennial ryegrass and red clover. However, the rate of decline in digestibility with time was greater with perennial ryegrass than with red clover.

3. Calves given silage of red clover as the sole feed ate more dry matter and grew faster than calves given grass silage (P <0·001) but supplementation with barley reduced the intake of red clover silage to a greater extent than that of perennial ryegrass silage. Barley supplementation increased live-weight gain of calves given perennial ryegrass from 0·32 to 0·83 kg/day and that of calves given red clover from 0·63 to 0·99 kg/day (interaction P <0·05). The results did not indicate a higher net efficiency of utilization of the legume. Date of cut had no significant effect on dry-matter intake but earlier cutting resulted in an increase in live-weight gain from a mean of 0·61 to 0·77 kg/day (P <0·001).

4. The results show that high rates of live-weight gain (0·74 kg/day) can be achieved by calves given silage of red clover and that earlier cutting of herbage for silage does not always result in higher intakes of dry matter. Supplementation of silages with barley can reduce markedly the difference in intake and live-weight gain apparent when the silages are given as sole feeds.

Intact male lambs from Limousin and Charmoise breeds, or crossbreds from F1 (Romanov × Limousin) ewes sired by Berrichon rams, were early weaned, intensively fed, and slaughtered between 20 and 40 kg of empty body weight. The whole carcass was chemically analyzed, and the results expressed on a shorn, empty body-weight basis.

Some between breed differences in the weight of fat and gross energy content were found: fat contents ranged from 179 to 212g/kg at 30 kg of empty body weight. The corresponding range for energy was 10·8 to 11·8MJ/kg of empty body weight. Differences between protein and ash contents were limited, from 154 to 165g/kg empty body weight, and from 31 to 33g/kg empty body weight respectively.

At the same empty body weight Charmois lambs (a small sized breed) contained more fat, less water and less protein than the crossbreds. Values obtained on the Limousin lambs were intermediate.

There was no evidence of diet or growth rate effect on chemical composition when compared with published data obtained from more conventionally fed lambs.

Nine Cheviot × Shetland castrated male lambs from a group of 24 of 28 kg initial live weight, were subcutaneously implanted with a combination of 60 mg trenbolone acetate and 12 mg oestradiol-17β at 105 days and again at 45 days before slaughter. Of the remaining lambs, nine were untreated and six were slaughtered at the start of the experiment as part of a comparative slaughter procedure. The lambs treated with the anabolic preparation grew significantly faster (P < 0·05), converted food to live weight and estimated carcass gain more efficiently, had heavier carcasses which were larger, and had greater estimated gains for protein, moisture and ash. Implanted animals also tended to have a smaller deposition of carcass and kidney fat, but significantly heavier kidneys and less wool when the latter three weights were related to empty body weight. The mean values for plasma urea and serum total protein as indicators of protein metabolism were significantly decreased and increased respectively in treated lambs, but no other significant differences in blood metabolites and hormones were recorded. A significant increase in teat length of implanted lambs indicated the oestrogenic nature of the anabolic preparation.

The effects of 18 buffalo sires, used in 2 years of a progeny-testing programme, on the subsequent lactation performances of their mates, were investigated from a study of 685 lactation records. The traits studied were: milk production, lactation length, length of post partum anoestrus, number of services per conception and length of service period (calving to conception). Parity of calving and sire had a significant effect on 305-day milk yield and lactation length of the mates. Between the 2 years, the sires did not differ for any of the traits of their mates. Although the breeding value of the sires, high or low, did not differ significantly, the sires with high breeding value tended to depress the milk production in the subsequent lactation of their mates and vice versa (r= −0·05). The birth weight of the calves significantly affected milk production. It was concluded that all methods of sire evaluation are likely to be biased by the effect of sires.

1. Measurements of digestible energy intake, live growth and carcass measurements were conducted with 96 individually housed pigs (48 male and 48 female) given the same diet at four feeding levels (ad libitum; Agricultural Research Council daily digestible energy intake (C); C–12·5%; and C–25% daily digestible energy intake. The pigs were slaughtered at one of six live weights (45, 60, 75, 90, 105, 120 kg).

2. Prediction equations of average daily live-weight gain and introscope P2 backfat thickness on the hot carcass (hot P2) were developed as functions of average daily digestible energy intake for males and females at varying live weights. The relationships found were 20·8 g live-weight gain per MJ digestible energy intake and 0·81 mm hot P2 backfat thickness per MJ digestible energy intake from 25 to 90 kg live weight.

3. Compared with feeding level C, C –25% produced no difference in feed conversion ratio, reduced shoulder maximum, mid-back and loin minimum backfat thickness by 6–8 mm (14–4%), 4–2 mm (168%) and 4–1 mm (17–5%) respectively (P<0·01) and increased eye-muscle area by 2908mm2 (10·9%).

4. Compared with females, males reached slaughter weight 9·4 days earlier, increased daily live-weight gain by 64g, increased feed conversion ratio by 0·3, had 1·6mm less hot P2 backfat thickness, had less backfat at all mid-line positions and showed no difference in eye-muscle area.

Insulin, thyroxine and tri-iodothyronine concentrations were measured in samples of blood from 175 Friesian bulls, aged between 2 and 7 years, which were being progeny-tested for milk production. Least squares regression coefficients were estimated for these hormone levels on time of day and time after feed at sampling and age of bull. Correlations between hormone levels and Improved Contemporary Comparisons of the bull, a measure of his daughters' milk production, did not differ significantly from zero, suggesting that simple spot estimates of levels of these hormones in bulls would not supply useful predictors of daughters' production.

1. Three ultrasonic machines (Sonatest TE/6, Scanoprobe 731 and Scanogram 721) and the ruler probe were compared as techniques for estimating carcass introscope and caliper measurements of P2 backfat thickness on each of 96 pigs. The effect of operator experience was examined with the Sonatest and Scanoprobe machines. Scanogram measurements of P2 backfat and eye-muscle area were evaluated using two methods of restraint (crate and nose rope).

2. The Sonatest was judged to be more precise (increased R2) than the Scanoprobe in predicting P2 backfat depth. Operator experience improved Scanoprobe precision but had little effect with the Sonatest. Ruler probe R2 was intermediate between the Sonatest and Scanoprobe.

3. The Scanogram was the most precise live P2 backfat measurement technique. R2 was not affected by method of pig restraint.

The effect of barley level and monensin on feedlot performance by lambs and steers was investigated in two experiments. Monensin was given at 0 and 33mg/kg of food in lamb and steer diets, which contained bailey at levels from 300 to 900g/kg. Food consumption by lambs was not affected by monensin but intakes decreased with increasing levels of barley (P < 0·05). Food intake by steers decreased in a linear manner with increasing levels of barley (P < 0·01) and averaged 80g/kg lower when monensin was fed (P < 0·05). Monensin improved lamb gains by 350g/kg (P < 0·001), but had no effect on steer performance. Feeding monensin improved average food efficiency in lambs and steers by 27 and 4%, respectively. Carcass characteristics were not influenced by monensin, but heavier carcasses (P < 0·01) in steers given the high barley rations were also fatter (P < 0·001).

An analysis of published data on the effects of feeding frequency on cattle gave the following results. On average, increasing feeding frequency increased average daily gain by 16·2±4·8%. The efficiency of growth was increased by 18·7±60·%, indicating that improvements in average daily gain were due largely to improvements in efficiency of food utilization. Much of the improvement in average daily gain and efficiency of food utilization was attributable to increasing feeding frequency from one or two meals per day to four, but there was some evidence of further improvement at higher feeding frequencies.

In terms of experimentation it was concluded that, in general, nutritional or genetic comparisons of growth and efficiency should be carried out with a strict control of feeding frequency. In terms of animal production it was concluded that cattle should be fed at least four times daily to ensure maximum food efficiency for growth.

The magnitude of the response of average daily gain to feeding frequency was dependent on several experimental variables. In particular, the response appeared to be greater when the level of average daily gain was low and when the level of concentrates was high. The variables examined seemed unable to account wholly for the differences in response found in different experiments. Predicting the magnitude of the response under defined experimental conditions therefore remains extremely difficult.

Although rather more limited, results with sheep supported the conclusions drawn from the results with cattle.

A study was made of the performance of different grades of Friesian × White Fulani crosses using 12 years' records from 1967 to 1978. Milk yield increased progressively with increases in the proportion of Friesian genes. Lactation length also showed a similar trend, with a difference between 1/2 and 7/8 grades of 41 days. Calving intervals averaged approximately 390 days and did not differ among grades. Calf mortality was high, varying from 16 to 29%. The optimal genetic contribution from the Friesian for this environment is considered to be higher than 75 %