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.

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.

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.

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.

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.

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.

In two experiments prepubertal gilts were injected with a combination of 400 international units pregnant mare's serum gonadotrophin and 200 international units human chorionic gonadotrophin. The gilts were housed either in contact with or isolated from mature boars. Data were obtained of ovarian activity determined immediately after gonadotrophin treatment and at the anticipated time of the second oestrus.

All treated gilts ovulated in response to the treatment and 83% displayed oestrus. Ovulation rate varied both within and between experiments, in experiment 1 the range being 7 to 19 corpora lutea and in experiment 2, between 5 to >30 corpora lutea. Four distinct types of behaviour were observed at the time of the second cycle: ovulation associated with oestrus; ovulation without oestrus; oestrus but no ovulation; and a return to a prepubertal state with no oestrus or ovulation. The presence of boars enhanced the maintenance of cyclic activity. Overall, more gilts displayed a second oestrus (33/39 v. 19/41, X2 = 11·2, P<0·001), and more had a second ovulation (32/39 v. 24/41, X2=4·2, P<0·05) when boars were run with the gilts.

Nineteen prepubertal gilts were injected with a combination of 400 international units pregnant mare's serum gonadotrophin and 200 international units human chorionic gonadotrophin. Blood was sampled throughout the ensuing oestrous cycle and assayed for progesterone and oestradiol-17β.

Eighteen gilts had vulval development consistent with oestrus within 5 days and had ovulated by day 12. Oestradiol levels in the plasma were elevated between days 2 and 6, and progesterone concentration increased between days 6 and 10 due to the establishment of functional corpora lutea. Progesterone concentration in the luteal phase was related to ovulation rate (r = 0·72, P<0·001).

Three types of cyclic activity followed the luteal phase and a characteristic hormone profile was established for each. Five gilts exhibited a second ovulation accompanied by signs of oestrus. They had a second peak of oestradiol around days 24 to 26 and a subsequent rise in progesterone concentration. Four gilts displayed vulval development at this time but did not ovulate. A peak of oestradiol was detected. The remaining gilts did not display oestrus, nor did they ovulate. Oestradiol and progesterone concentrations remained basal in these gilts. The ovaries of prepubertal gilts treated with this combination of gonadotrophins produce normal patterns and levels of oestradiol and progesterone. Cyclic activity is not always maintained, probably due to differences in the maturity of the hypothalamic-pituitary-ovarian axis.

Twenty-seven mature boars were housed in individual pens for 9 weeks under one of the following social conditions: isolated from female pigs; near sexually non-receptive female pigs; and near sexually receptive female pigs. The sexual behaviour of the boars during the 9-week treatment period was observed weekly in standard 15- min tests. The sum of the individual courting behaviour activities and the total time spent ejaculating were significantly greater for the boars housed near either sexually receptive or sexually non-receptive females than for those boars isolated from female pigs (P<0·01 and P<0·05, respectively). Although the boars housed near sexually receptive and sexually non-receptive females achieved 43 and 38% more copulations, respectively, than those isolated from females, the difference was significant only for the latter comparison (P<005). There was no consistent difference in testosterone concentration over a 12-h period between boars housed near sexually-receptive females and those isolated from females.

Thirty-six pigs were weaned at 21 days of age and were given diets supplemented with either dicalcium phosphate (DCP) or defluorinated rock phosphate (DFP) from 4 weeks of age until slaughter at 50 kg live weight. From 4 to 9 weeks of age the diets contained either skim milk powder (SKIM) or soya bean meal (SOY) as the main protein supplement. The dietary treatments were arranged in a 2 × 2 factorial design. From 9 weeks of age until slaughter, SOY was the only protein supplement used. Four 7-day measurements of phosphorus, calcium and nitrogen balance were made on each pig. Faecal endogenous P was estimated in two pigs per treatment by the 32P dilution method.

There were no significant effects of P supplement on performance or on apparent absorption, true absorption or retention of P. The apparent absorption and retention of Ca were both 0·07 lower with DFP than with DCP in the period from 9 weeks of age to slaughter (P< 0·001).

From 4 to 9 weeks of age there was no effect of protein supplement on performance. From 9 weeks of age to slaughter, when all pigs were given SOY, those which had received SKIM in the previous period grew slightly faster (P<0·05); their growth-rate overall, from 4 weeks of age to slaughter, was also significantly better (P <0·05).

Pigs given SKIM showed a higher apparent absorption of P (P < 0·001) and higher apparent absorption (P<0·01) and retention (P<0·001) of both Ca and N from 4 to 9 weeks of age. Again, there were carry-over effects in the period from 9 weeks of age to slaughter, although the trends observed in the first period were reversed; pigs previously given SKIM showed significantly lower apparent absorption and retention of both P and Ca, and apparent absorption of N, than those previously given SOY.

There were no significant effects of dietary treatments on the ash, Ca or P content of the fourth metacarpal.

The heat losses of 24 individually housed pigs (initial body weights 20·0 to 31·8 kg) were measured for periods of 7 days at environmental temperatures of 10, 20 and 30°C. Within each environmental temperature three levels of air movement, 3, 33 and 56cm/s, were applied for a 2- or 3-day period either in an increasing or decreasing order.

Heat loss was dependent on the environmental temperature and level of air movement to which the animals were exposed. The decrease in total thermal insulation at the highest air movement was equivalent to reducing the air-ambient insulation to almost zero. In terms of its thermal effect a 5cm/s increase in wind-speed was equivalent to a 1°C decrease in temperature.

The lower critical temperature increased with increase in air movement from 19° at 3cm/s to 25° and 30°C at 33 and 56cm/s, respectively. Between air movement rates of 33 and 56cm/s, a 1°C decrease in critical temperature resulted from a 5·3cm/s decrease in air movement.

The effect of increasing air movement from 3 to 56cm/s was to increase the animal's maintenance energy requirements from 706 to 881 kJ/kg0·75 per day at 10°C, from 490 to 715 at 20°C and from 517 to 625 at 30°C.

Thirty-six British Friesian castrated male cattle (steers) were included in an experiment to measure the response in live-weight gain and body composition to feeding barley-based diets containing increasing levels of formaldehyde-treated soya bean meal. The response was measured between 100 kg and 350 kg or 450 kg live weight. The basal diet of pelleted whole barley and 10% ground oat straw contained 16·6g to 38·5 g nitrogen per kg dry matter. There were no overall differences in live-weight gain or in feed intake. Between 100 kg and 250 kg live weight, live-weight gain increased significantly from 1 08 to 1·24 kg/day when the lowest and highest nitrogen diets respectively were fed (P<0·05). Animals given the highest nitrogen diets also consumed significantly more feed (P<0·05). Conversely, in the subsequent growth period between 250kg and 350kg live weight, live-weight gain decreased from 109 to 0·89 kg/day when the highest nitrogen diet was fed. There were no significant differences in feed intake.

Groups of four animals per treatment were slaughtered at 365 kg and 465 kg fasted live weight. When animals were fed 23·7 g nitrogen per kg dry matter and slaughtered at 365 kg fasted live weight there was significantly more omental fat (P<0·05) and the fat depth at the 12th rib was greater than in animals fed the higher levels of nitrogen. The differences in omental fat weight between the 23·7 g nitrogen and 16·6g nitrogen per kg dry matter diets were not significant. The proportion of crude protein (nitrogen × 6·25) in the boneless 9-10-1 lth rib of animals fed 23·7 g nitrogen per kg dry matter was the lowest of all diets and significantly less than the two highest nitrogen diets (P<0·05). When similar animals were slaughtered at 465kg there was a non-significant trend for omental fat weight and fat depth at the 12th rib to decrease as the nitrogen content of the diet increased.

The effects of reducing the feed intake of 12 winter-calving (Hereford male × British Friesian female) cows to the maintenance level for 6 weeks from week 10 of lactation were investigated during two consecutive lactation periods. Initially, six cows were in their first and six in their third lactation. In each year the period of ‘underfeeding’ was preceded by a period of ‘adequate feeding’ (maintenance plus milk production requirements) and succeeded by a period of ‘refeeding’ (2 × maintenance). Changes in body water, estimated by the dilution of tritiated water and deuterium oxide at the end of each feeding period, were used to calculate changes in body tissue. Milk yield during the period of ‘adequate feeding’ indicated that individual cows differed markedly in milk production potential. During ‘underfeeding’ milk yield was related to lactation potential. Cows of higher potential tended to maintain higher yields than those of lower potential but in doing so they incurred higher body-weight losses. The ‘refeeding’ period did not result in significant increases in milk yield. The weight losses during ‘underfeeding’ consisted mainly of fat but some cows apparently mobilized relatively large amounts of protein. More fat per unit body weight loss was mobilized by the heifers than by the cows, which, on the other hand appeared to mobilize relatively more protein. On ‘refeeding’, only a few cows were able to achieve complete tissue repletion.

Mean daily milk yield, fat concentration and protein concentration in the milk of 579 303 British Friesian, 6 608 Shorthorn, 27 374 Ayrshire, 19 529 Jersey and 19 760 Guernsey cattle were recorded monthly from August 1978 to July 1979 inclusive, and classified by breed, parity, stage of lactation, and five geographical areas according to the location of the herd. Parameters of the function Y(n) = anbecn were estimated for each breed/parity/area group for yield, fat concentration and protein concentration (b and c describe the shape of the curve, a is a scalar, n the week of lactation and e the base of natural logarithms). Systematic deviations from the function were associated with the season of production, reflecting the spring and summer flush of milk yield. Fat and protein concentrations also exhibited seasonal variations from the underlying curve. After correction for the seasonal fluctuation in production, there was no variation in total yield, fat concentration or protein concentration associated with the month of calving.

Three groups of winter-housed Friesian cows were fed according to maintenance and production requirements on dairy cake and poor quality hay for 5 weeks (5 cows), 4 weeks (4 cows) or 2 weeks (3 cows). They were then treated as one group with two injections of 500 μg cloprostenol 11 days apart to synchronize oestrus, followed by insemination 72 and 96 h after the second treatment.

Blood samples were taken for β-carotene estimation 1 day before the first cloprostenol injection, 3 days before the second injection, and the day after the second insemination. Conception was confirmed by rectal examination. Haematological parameters and metabolic profiles for all 12 cows were in the normal range and condition scores showed no correlation with time of conception. However, plasma β-carotene levels declined rapidly and uniformly between the three sample points for all cows. The individual animal means were directly correlated with length of time on the described diet and with time of conception (P<005). A theory of β-carotene involvement in ovarian function is advanced.

In the first phase of the Meat and Livestock Commission's beef breed evaluation programme, cattle were slaughtered at a fixed subcutaneous fat percentage in carcass. Slaughter point was determined from fat areas measured over the m. longissimus at the 10th and 13th ribs by the Scanogram ultrasonic machine.

The accuracy of the slaughter procedure was examined using data for 1367 cattle from the first 3 years of the programme. Subcutaneous fat percentage predicted from the ultrasonic measurements was compared with the percentage estimated by visual assessment of carcass fat cover. The s.d. of the difference between the two was 1·65.

Data for a subset of 313 cattle were used to examine the relationships between the ultrasonically measured fat areas and actual subcutaneous fat percentage obtained by dissection. The residual s.d. for the prediction of subcutaneous fat within breed and production system was 1-18.

The level of accuracy achieved was considered to be satisfactory within the context of the beef breed evaluation programme.

Sixteen pork carcasses were purchased from those exhibited in Class 146 at the Royal Smithfield Show 1978 (i.e. pork carcasses of 48 to 61kg dead weight, age <5 months). Eight had thinner backfat than the average for the class (‘very lean’ group with 6 mm fat over m. longissimus at the last rib and estimated lean content in side of 63%), while eight had thicker backfat than the average (‘lean’ group with 12 mm fat over m. longissimus at the last rib and estimated lean content in side of 57%). Both groups were leaner than the national average. The carcasses were returned to the Meat Research Institute for eating quality assessments. Muscle quality was similar in both groups. Toughness (assessed instrumentally), tenderness and flavour (assessed by taste panellists) were also similar. Juiciness was lower in the ‘very lean’ group but was not matched by higher cooking losses and the difference was considered to be relatively unimportant. In conclusion, the eating quality of pork is maintained at very low values of carcass fatness.

The twinning rate of Finn × Awassi ewes in a breeding management system which included three breeding periods a year, namely, June, September and December-January, was studied in animals mated at their natural or induced oestrus.

A similar number of lambs per ewe lambing was obtained from the ewes mated either at the induced oestrus in June or September, or at their natural oestrus in December. A significant decrease was found in the twinning rate of the ewes mated in January after hormone treatment. The conception rate was highest in the ewes mated in December-January.