Information relating to the carcass composition of grass-fattened beef cattle in the UK is not only limited in extent, but is also frequently uni-dimensional, in that the quantitative changes in carcass composition with time cannot be readily assessed. Furthermore, the methods used in selecting animals for slaughter (the visual appraisal of condition) introduces a source of non-random variation that cannot be removed with statistical confidence.

The primary objective of the analysis reported here, therefore, was to evaluate the effects of time on carcass composition and thereby provide information upon which objective production strategies could be based.

48 fattening steers and heifers (16-19 months old and 355 kg liveweight) of two contrasting breed types (Charolais x Hereford x Friesian and Hereford x Friesian) were summer grazed at a stocking rate of 5 animals per hectare. The animals were randomly allocated (at the start of the grazing season) to three slaughter points covering a 12 week period from early July to early October. The commercial saleable meat yield of the left side of each animal was measured together with compositional data from rib sample joints.

The national cow herd consists of 1.64m dairy and 0.43m beef cows. They produce a total of 1.76m reared calves annually. Of these 0.42m heifers go as herd replacements, leaving 0.46m heifers and 0.88m males available for beef production. There is a 2:l ratio of males to femaies in the population of calves available for beef production. Also, there are few straightbred dairy heifer calves available and the mean birth date of heifer calves for beef production is later than that cf males. The objectives of the present experiment were (i) to compare the performance and carcass composition of non-implanted and implanted heifers and steers and (ii) to compare the carcass composition of serially slaughtered non-implanted and implanted heifers.

Sixty tour (48 female and 16 male) Spring born Hereford x Friesian calves (initial live-weight 45 kg) were purchased and reared on milk replacer and concentrates. After 81 days they were blocked on weight and assigned from within sex type to 8 treatment groups.

An experiment was designed to assess the effect of altered growth potential (oestradiol status) on the response of intensively-reared steers to variations in UDP concentration. Observed growth responses were compared with those predicted by current protein evaluation schemes (ARC, 1980, 1984).

Nine steers implanted with oestradiol -17β (‘Compudose 365’, Elanco Ltd) and nine non-implanted steers were fed on each of four diets from approximately 130 to 300 kg liveweight. The all-concentrate, iso-energetic diets used supplied a constant level of RDP slightly above that recommended by ARC (1980) and levels of UDP both above and below ARC (1980) recommendations (Table 1).

Dry matter intake was recorded daily and liveweight weekly. The metabolisable energy system (MAFF, 1984) and the ARC (1980, 1984) protein evaluation system were applied to the feed intake and diet composition results recorded during the experiment in order to generate predictions of growth rate for each treatment which could then be compared with the observed growth rate.

Eight breeding companies contributed foundation stock for a joint experiment on lean growth at the Animal Breeding Research Organisation (ABRO) and Wye College. All animals were test-mated to halothane positive (HP) reactors and incidences of HP reaction among progeny were used to estimate the frequency of the halothane gene (n) in the original herds. Estimated incidences of HP were compared with those observed in an earlier 1979 survey.

260 British Landrace (LR) were test-mated to HP (expected nn) LR at Wye, and 186 Large White (LW), including 18 boars standing at national AI centres, were test-mated to HP LR, Pietrain-Hampshire or LR x (LW x Norwegian Landrace) at ABRO.

Offspring were given a 4-minute halothane test at an average age of 50 days in LW and 76 days in LR. Numbers tested and incidences of reaction are shown in Table 1. Herds are coded ‘A’ to ‘I’ for anonymity. Purebred LR in herds A, C, D, E, H and I were halothane testec in advance and only halothane negatives (HN) were supplied for test-mating.

Precise, unbiased estimates of genetic parameters, such as heritability and genetic covariance, are necessary to optimise breeding programs and to predict rates of change for various selection schemes. A classical method of estimation is to use high and low selection experiments. We consider two generation selection experiments when observations in the parental generation are only taken on one sex, resulting in half-sib family information. We consider cases of two standardised traits, with zero mean and unit variance, and assume that the traits are normally distributed. The genetic and phenotypic variance-covariance matrices for the traits are denoted by G and P respectively. The genetic variances and covariances of the standardised traits are then heritabilities and co-heritabilities.

The construction of other designs is examined, assuming the phenotypic correlation of rp between traits is known. For simplicity, comparisons of designs are developed by considering the variance of the genetic variances when the traits are uncorrelated both phenotypically and genetically.

Five genotypes were compared as sires of crossbred ewes from Scottish Blackface dams. These included Border Leicester (BL), New Zealand Romney (R) (from two group breeding schemes where selection had emphasized litter size), and three lines from the composite A.B.R.O. Damline (DL). Selection of the male and female lambs in the purebred DL flock was:

1. a) for an average of 5.5 years on a Ewe Index of eight week litter weight (Martin and Smith, 1980).

2. b) for an average of 3.5 years on a Testis index, combining testis size (adjusted for body weight) and Ewe Index of eight week litter weight both components receiving approximately equal weight and

3. c) a random bred control.

These five genotypes (two rams per genotype per year for five years) were group mated (sires of individual ewes were not known) with Scottish Blackface ewes on an upland farm in Ayrshire.

The Romney sheep group breeding scheme was initiated in 1979. Twelve pedigree breeders formed a Nucleus flock (N), at Wye College, each contributing ten “elite” ewes identified as prolific. The minimum entry requirement was that each ewe should have given at least twins at the previous lambing. The elite ewes were then performance tested in a common environment and those failing to give a multiple litter were replaced by other candidates from the flock of origin. The performance test was discontinued in 1982 when N was closed. Male and female replacements were chosen from the N-bred progeny. Replacements were selected on the basis of dam and sire's dam prolificacy record (live lambs born/ewe joined LLB/EJ)); ten ram lambs were chosen each year and thirty to forty ewe lambs. Ram lambs were used once as sires. Selection was for prolificacy with independent culling levels for tendency to prolapse, udder shape and breed type. A control flock (C) was set-up in 1982 by sampling at random within flock and age the twelve scheme member's flocks. Fifty pregnant ewes were assembled prior to the 1982 lambing. N and C were managed together apart from mating. No selection was applied to C.

In 1976, ten members of the Welsh Mountain Breed Society, established Camda Cynwyd Ltd as a co-operative society. The stated aim is to breed slightly bigger Welsh Mountain ewes that lamb easily and rear heavier lambs whilst retaining the hardiness and other beneficial traits of the breed.

A nucleus flock of 150 ewes was created in 1976 with the more productive ewes out of each member's MLC recorded flock. Camda hired facilities for keeping and recording the nucleus flock at the ABRO hill farm, Rhydglafes, North Wales for six years. Anticipating the disposal of the ABRO farm by the AFRC in 1984, a lease was obtained on a 340 acre hill farm at Cernioge Mawr, Pentrefoeias, and the flock transferred there during the summer and autumn of 1982. Each year, fifty high performance, mature ewes (immigrants) were introduced to the nucleus from members flocks, until 1984 when it was closed.

Field trials were run to evaluate the commercially available preparation Fecundin (Cooper/Glaxo) which is a hormone immunoneutralization technique for boosting lambing percentage. Fecundin is a vaccine produced by linking androstenedione with a protein to form a conjugate which when formulated with an adjuvant stimulates an active immune response within the ewe. Antibodies produced against the vaccine bind with naturally occurring androstenedione present in the blood leading to a moderation of feedback mechanisms which suppress follicular development. The result is higher ovulation rate leading to production of more lambs. Fecundin was developed and widely tested in Australia and New Zealand. The objective of these trials was to evaluate the levels of response obtained in a range of common U.K. sheep breeds under farm conditions, to monitor the effects of weight changes around mating on this response and to make an economic assessment of this technique of increasing lambing percentage.

The availability of the vaccine Fecundin ® (Coopers Animal Health) could have far reaching effects on commercial lamb production in the UK. Immunisation with Fecundin is claimed to increase ovulation rate with a corresponding effect on subsequent lambing rate.

Trials in Australia, New Zealand and the UK have produced responses to immunisation in lambing percentage (lambs reared/100 ewes mated) ranging from −5% to +67%. The trial being reported set out to examine the effect of treatment with and without oestrus synchronisation in an upland flock of Scottish Blackface ewes being crossed with Texel rams and with a normal lambing percentage of around 130.

One hundred and sixty nine 1, 2 and 3 crop (2.5,3.5 and 4.5 year old) Scottish Blackface ewes were allocated in September 1984 between four treatments on the basis of age, liveweight and condition score.

Observations of the effect of the immunogen ovandrotone-albumin (Fecundin ® Coopers Animal Health) when used in ewes mated in their breeding season have shown that with a boost-tupping interval (BT) of 21 days for natural oestrus and 28 days for synchronised oestrus there was an increased fecundity but that treated ewes lambed a little later than controls.

While this latter effect was not dramatic it was felt advisable to investigate the use of Fecundin as a means of boosting lamb production in an early lambing flock in conjunction with progestagen and PMSG treatments.

Active immunisation against androstenedione (Fecundin, Coopers Animal Health) increases ovulation and lambing rates. A study undertaken during the 1984-85 breeding season in randomly cycling ewes mated during October and November showed an increase in lambing rate of 24 lambs/100 ewes mated amongst ewes treated with Fecundin (Vipond, Keeling and Hunter, 1986). Fecundin increased the Incidence of triplet and quad births, suggesting that the greater benefit from the product would be derived in a situation where management could ensure the survival of additional lambs. The early lambing flock is such a case. Ovulation rates tend to be lower than later on in the breeding season, so fewer triplets might be expected amongst treated ewes. Management tends to be of a high standard, and the value of the early finished lamb is high.

The main factor limiting fecundity in sheep is the low ovulation rate (Hanarahan, 1980). The relationships between body condition, level of nutrition and ovulation rate, and the ability to increase fecundity by flushing ewes prior to mating, are all well established (Gunn, 1983). In upland ewe flocks, flushing is generally attempted by the use of saved autumn pastures. However, the seasonal variation in grass growth often results in the degree of flushing desired not always being possible and leaving the flockmaster seeking a viable option.

The present investigation examined two possible alternative strategies for increasing the fecundity of upland ewes. Improving body condition prior to mating by supplementary feeding was compared with the recently developed technique of increasing ovulation rate by active immunisation against androstenedione (Scaramuzzi, Cox and Hoskinson, 1982).

Although there is some understanding of the effects of immediate levels of nutrition on ovulation rate and embryo wastage, it is not yet possible to predict the reproductive performance of ewes at pasture in the autumn. In many situations sward height declines over the pre- and post-mating period but herbage intake and reproductive performance under these circumstances have not been described. Furthermore, responses in reproductive performance to supplementary feeding at pasture in the autumn have been variable. It may he possible to explain some of this variation in terms of sward height and the substitution rate of herbage by the supplement. This paper reports 2 experiments which were conducted to describe (1) the herbage intake by ewes grazing swards at different heights and when supplements were offered, and (2) the reproductive performance of ewes given supplements as sward height declined.

The new concern in Britain which links diet to health is likely to have a major impact on the agricultural and food industries. Five years ago consumers were not interested in the health issue but now consumer groups are lobbying for change. Health has become the second most important factor considered by a housewife when shopping for her family, the first being whether the food is appetizing.

Both the DHSS and MAFF have accepted, the 1984 COMA panel's report on diet and cardiovascular disease which sets out a programme of preventive measures with recommendations to the general public, medical practitioners, health educators, food producers, manufacturers, distributors and caterers and to Government. Specific changes in the British diet are advocated for the first time with a suggested reduction in saturated fat intake of 25% and in total fat of 15%.

1. 1 The relationship between diet and health is now a major factor in the development of production and marketing strategies for the British meat industry, following Government recommendations that people should be encouraged to eat less fat. It has emphasised the need for accurate information on the body composition of national livestock populations and the fat content of the meat and meat products derived from them. This paper collates the information available for cattle, sheep and pigs, and provides base-line (1984) estimates of national lean and fat production. Changes that have taken place over the past ten years are also examined.

2. 2 The basic framework for making estimates was the distribution of carcasses between fatness ranges in the national carcass classification schemes operated by the Meat and Livestock Commission (MLC). The distribution for cattle was obtained from a random 1 in 3 sample of beef carcasses classified (0.25 of all clean beef carcasses were classified).

3. 3 A computer spread-sheet was constructed relating the midpoint means of the fatness ranges to carcass tissue proportions and chemical composition. Regressions for predicting carcass lean and fat content were calculated from accumulated data from surveys of commercial carcasses and breed evaluations for cattle (Kempster, 1986), for sheep (Kempster, Jones and Wolf, 1986a) and for pigs (Diestre and Kempster, 1985). Key regressions are given in Table 1. Carcass lean and fat are defined as in the standard MLC tissue separation procedure. Regressions for estimating carcass lipid content: were obtained using data from several studies. The principal study involved carcasses from breed comparison trials (MAFF/MLC, 1982). Details of the other data sets are given by Kempster, Cook and Grantley-Smith (1986b). Key relationships are given in Table 2.

4. 4 Estimates of the composition of carcasses in different classification fatness ranges are given in Table 3. These are for 'clean' cattle, sheep and pigs, but estimates were also made for cull cows and cull ewes.

5. 5 National estimates of carcass composition and the weights of lean and fat produced in 1975/77 and 1984 are given in Table 4. The carcass composition of beef was the same in 1974/76 and 1984 but the average carcass weight has increased by 20kg. The implication of this is that changes in breed and production system have created the potential for leaner carcasses but that the beef industry has preferred to exploit this potential by increasing carcass weights. An increase of 20kg is equivalent to about 15gAg separable fat in carcass on the basis of typical regressions within breed and system.

   The carcasses of clean sheep in 1984 were estimated to be slightly lighter and leaner than those in 1977. Information on marketing patterns suggests that there has been little change in production methods (as far as they affect composition) and that lambs are now being slaughtered early, possibly stimulated by the pattern of Guide Prices in the EEC Sheep Meat Regime.

   In marked contrast to cattle and sheep, the separable fat content of the average pig carcass has fallen from 274g/kg in 1975 to 228g/kg in 1985, with a small increase in carcass weight. It is estimated that the increase in the use of entire males has contributed 5g/kg to the overall change.

6. 6 The estimates in the paper are considered to be the best available with current information but because of the limitations of the data may be subject to error. Possible sources of error are discussed by Kempster et al (1986b). The authors would be pleased to know of data relating physical and chemical composition that could be used to refine the estimates.

Compared with pigs, cattle and sheep lay down much of their carcass fat between the muscles (intermuscular fat) and a smaller proportion on the carcass outer surface (subcutaneous fat). The skin is also removed from cattle and sheep during the dressing process, and this results in surface irregularities on the subcutaneous fat. Because of these species differences, simple methods of estimating carcass lean proportion, based on the depth of subcutaneous fat, have been less successful in ruminants. In particular, there has been no counterpart in the beef and sheep carcass classification schemes to the optical probe used so successfully in the pig sector. But there is a need for an objective method of classifying beef and sheep carcasses according to their lean meat proportion, and in this study the speed of ultrasound technique was examined as a possible contender for this role.

1. 1 Visual assessments of subcutaneous fat cover are used in the Meat and Livestock Commission's Sheep Carcass Classification Scheme to estimate meat yield. (Details of the scheme have been given by Meat and Livestock Commission, 1980.) The scheme is operated in over 100 abattoirs and covers approximately 0.25 of the GB kill. Objective measures of fatness may improve the precision of predicting carcass composition, aid standardisation and stimulate the uptake of the scheme by creating greater confidence.

2. 2 Previous MLC trials with either a simple Ruler Probe or equipment developed for use in pig carcass classification such as optical or automatic-recording probes have indicated only moderate success with sheep carcasses. The precision achieved with probe measurements was no better than visual scores, but additional precision resulted from combining both techniques (Kempster, Chadwick, Cue, Grantley-Smith, 1986).

Most bacon carcasses in Britain are measured, within the national Pig Carcase Classification Scheme operated by the Meat and Livestock Commission (MLC), for P2 fat thickness, shoulder and loin fat thicknesses and carcass length. Bacon curers use these measurements to define the grading schedules most appropriate to their buying requirements.

There is debate about the value of mid-line fat measurements and length as indicators of carcass quality. The scientific evidence indicates that mid-line measurements are less precise predictors of carcass lean content than P2, and that the mid-line loin measurement is superior to the mid-line shoulder measurement.However, it is argued that the mid-line measurements may have special regional value: eg as predictors of carcass lean content in individual joints. The analysis reported uses a computer model (PIGRADER) to examine overall lean in carcass, the composition of individual joints and joint proportions for alternative grading schedules.

The firmness of backfat in pigs is an important aspect of meat quality which is influenced by the chemical composition of the fat tissue. This is affected by the amount (thickness) of fat and by diet. Thin backfat Is relatively soft but nutritional manipulation can potentially overcome this problem.

This work compared fat thickness in pigs on a commercial farm fed a concentrate diet (CD) or a skimmed milk - balancer diet (SM). The low level of oil in SM was likely to be a key factor in increasing firmness.