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Results on the body and carcass composition of 7885 lambs sired by 371 rams of 15 different breeds mated to Romney cast-for-age ewes are given. Trials were run at the Ruakura Agricultural Centre and the Manutuke Research Station from 1963 to 1972. Lambs of the different breeds were slaughtered at the same average age so that differences between breeds/crosses in liveweight and carcass weight reflected differences in growth rate. Ranked from heaviest to lightest mean age-adjusted carcass weights, lambs sired by the Dorset Horn, Poll Dorset, Hampshire, Border Leicester, Suffolk, Dorset Down, South Suffolk, and South Dorset Down produced the heaviest carcasses, and those sired by the Cheviot, Southdown, English Leicester, and Ryeland were intermediate. The Lincoln, Merino, and Romney sired carcasses were lighter. The longer-woolled Romney, Merino, and Lincoln had lowest dressingout percentages based on full liveweights and the short finer-wooled breeds such as the Southdown, Dorset Down, and Poll Dorset/Dorset Horn dressed 2-3% higher. When compared at the same carcass weight, lambs sired by the Southdown followed by the Ryeland had the fattest carcasses and those A94091Received 26 September 1994; accepted 27 April 1995 1 Deceased sired by the Suffolk, Cheviot, and Dorset Horn produced the least fat, leanest carcasses. The Southdown, Dorset Horn, South Dorset Down, and Poll Dorset crosses had the largest eye muscle areas for carcasses of similar weight.

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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...

Factors associated with differences in carcass conformation were studied in three experiments involving 85 pairs of lambs, half of which had been selected as having blocky conformation and half leggy conformation. Pairs of carcasses were matched for carcass weight and age at slaughter.The blocky carcasses contained more fat and less red meat and bone than the leggy carcasses. They also had a higher proportion of the fatter cuts (loin, ribs, and flap) and a lower proportion of the leaner cuts such as the leg. A taste panel found the palatability characteristics of leg meat from both types of carcasses acceptable and did not differentiate between them. The differences in conformation strongly influenced the export grading of the carcasses, the blocky carcasses grading predominantly Prime Down Cross and the leggy carcasses mainly Prime Crossbred and Y.South down sires produced the blockiest carcasses and the other breeds studied produced the leggiest carcasses. Within-breed variation was also noted in one experiment where conformation differences were less extreme. The leggy carcasses came from animals that had heavier liveweights at slaughter than the blocky animals, although the hot carcass weights of both were the same.The results are discussed in relation to the New Zealand meat industry. The conclusion is reached that the blocky carcasses have no superiority in terms of meat content or proportion of high-priced cuts, and that in future more emphasis should be placed on economic characteristics and less on conformation in breeding and crossbreeding programmes.

Approximately 4,400 crossbred lambs from Southdown sires and Romney ewes were slaughtered at approximately 18, 23, and 28 wk of age over a 16-yr period. Live weights, carcass measurements, and chemical percentages were analyzed to estimate genetic and phenotypic parameters. Heritabilities of postweaning weights and gains were about .20. Heritabilities of fat and water percentages were about .35 adjusted for age. Heritability of kidney fat percentage was .53. Heritabilities of fat depth and muscle measurements ranged from .21 to .37. Crutch depth (h2 = .73) and cannon bone length (h2 = .74) were the most highly heritable carcass measurements. The genetic correlation between carcass fat and fat-free weight was .47 when lambs were slaughtered at a constant age. Fat-free weight was nearly uncorrelated with percentages of fat, water, and protein when lambs were slaughtered at the same age. Carcass measurements increased accuracy of selection for fat-free weight at a constant age very little compared with using only carcass weight. However, this does not mean that additional measurements are useless. The addition of carcass measurements to the selection criteria would result in correlated responses in chemical composition that more closely resembled direct selection for fat-free weight. Carcass weight would be of little value when used by itself to reduce fat weight adjusted for carcass weight. Direct measurement of carcass composition resulted in 1.6 to 2.6 times more predicted response for reduced fat weight than any combination of carcass weight and one fat depth measurement.