A comparatively rapid method for estimating the chemical composition of mutton carcasses has been reported previously (Barton & Kirton, 1956 and a detailed description of the procedure has been given by Kirton & Barton (1958). The method involved the cutting of a frozen carcass down the back-bone. One side was then sliced and the slices, consisting of frozen flesh and bone, were ground (minced) in a commercial grinder (mincer). Samples were drawn from the thrice-ground material and these were analysed chemically. Treatment differences between groups of carcasses have been detected using this procedure, but hitherto it was not possible to study the magnitude of any errors inherent in the method. MATERIALS AND METHODSTwenty Southdown-Romney cross wether lambs which had been used in an investigation into the effects of cortisone and hecogenin on wool growth and live weight were available for carcass analyses. No differences of any importance due to the effects of the drugs were observed on live weight or in carcass composition of these lambs; hence they were suitable for the present study.At slaughter the animals had an average live weight of 78 lb. (range 63-5-93-8 lb.) and their hot carcass weight averaged 39-2 lb. with a range of 31-2-43-8 lb. Slaughtering and dressing followed commercial practice; thus each carcass was headless and the bones of the lower limbs from and including the metacarpals and metatarsals were removed. The kidneys were removed but the perirenal fat was left intact in the carcass. The carcasses were placed in a chiller overnight and then they were frozen and stored until required. Following approximately a year of storage the frozen carcasses averaging by then 36-6 lb. in weight were brought in twos and threes to the meat laboratory for analyses.These carcasses while still frozen were divided down the back-bone using a meat band-saw, then each side was cut into four parts, namely, leg, loin, rib cut, and fore. (a) Jointing of a sideAll jointing was done with a band-saw. A cut was made between the last thoracic and 1st lumbar vertebrae and the rib (usually the 13th) was followed out to the flank. The loin, including all perirenal fat, was removed from the posterior part of the carcass by cutting between the last lumbar and the 1st sacral vertebrae and continuing this cut at right angles to the back-bone through to the flank. The loin contained six or seven vertebrae. In cutting at right angles to the back-bone a small tip of the ilium was invariably severed and this became part of the loin. The part designated as the leg comprised the remainder of the posterior portion of the side and thus included the greater part of the pelvis.The rib cut, consisting of the 9th, 10th and 11th ribs, was removed from the anterior portion by cutting midway between the 8th and 9th ribs and midway between the 11th and 12th ribs. The cuts were made from the back-bone through to the flank, but because of the necessity of cutting midway between the ribs it was not always possible to commence the cut between the app...

1. The carcass composition, the composition and characteristics of the subcutaneous and longissimus dorsi muscle fats, the volatile fatty acids of the rumen-reticulum fluid and the degree of flavour and odour of the cooked 12th rib chops of two groups each of fifteen Southdown–Romney cross ewe and wether lambs fed respectively white clover and perennial ryegrass have been determined. The lambs had been on treatment for 5 months and were slaughtered when about 9 months of age.2. The white clover-fed lambs had a mean live weight at slaughter of 94 lb ± 9 lb compared with 67 lb ± 7 lb for the perennial ryegrass-fed lambs. The carcasses of the white clover-fed lambs had greater (P < 0·01) amounts of fat.3. The iodine values of the subcutaneous fats of the white clover-fed lambs were highly significantly greater than those of the ryegrass-fed lambs and this result was consistent with the greater deposition of endogenous fat.4. The extra fatness of the white clover-fed lambs was consistent with their greater production of rumen-reticulum volatile fatty acids.5. The maj or differences in fatty acid composition of subcutaneous and intramuscular fats between pasture treatments were the highly significant increases in shorter-chain saturated and C15 branched-chain acids of the ryegrass-fed lambs. In addition, the subcutaneous fat of the ryegrass group contained highly significantly more octadecadienoic and octadecatrienoic acids while the 1. dorsi fat of the ryegrass group was highly significantly richer in stearic and oleic acids.

Carcass characteristics of Southdown rams from lines selected for high or low backfat depths (assessed ultrasonically at Position Cover the longissimus dorsi muscle at the last rib) were compared. Rams were 15-18 months old and average carcass weight was 29.5 kg fo{ the High-line (n = 36) and Low-line (n = 42) groups. When adjusted by covariance to the same carcass weight, animals from the High-line had higher dressing-out percentages, lighter weights of several internal organs, and shorter carcasses. At a constant side weight, the High-line sides contained 18% more dissectible fat and significantly lighter weights of muscle and bone. However, muscle to bone ratio and muscularity in terms of muscle weight per unit length were greater for the High-line group. The High-line carcasses contained a greater proportion of their weight in the rack and loin cuts. The greater weights of four dissectible fat depots in the High-line carcasses were the result oflarger rather than more adipocytes. The results show that selection on the basis of a single fat depth measurement resulted in significantdifferences in all measures of fatness, and also in several other carcass characteristics.

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Three experiments are reported in which the tenderness of meat from 171 steers of 6 breeds (Angus, Friesian, Jersey, Ayrshire, Galloway, and Red Poll) was measured as shear forces. Generally, differences between breeds for meat tenderness were not statistically significant, although the meat of Jersey cattle was significantly more tender than that of some o~he! breeds in one experiment, an effect which is consistent with overseas evidence. Some. significant breed effects were shown on the way in which post-mortem treatments, such as aging and pre-ngor storage temperature, affected meat tenderness. Other measurements madẽ n the muscles o~some of th.e steers indicated that Jersey cattle had the highest level of intramuscular fat III one experiment, but there were no appreciable differences in sarcomere length or muscle pH between breeds of cattle.