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    A study of the carcass composition and meat quality of Southdown sheep selected for differences in backfat depth : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, New Zealand
    (Massey University, 1988) Kadim, Isam Tawfik
    Southdown sheep from genetic lines that have been developed at Massey University by selecting for and against weight-corrected fat-depth measurements made ultrasonically on the live sheep, were evaluated for carcass and meat quality characteristics in 4 experiments, while their crossbred offspring from Romney ewes were evaluated in 2 experiments. No significant differences were found in daily live-weight gains between the two selection lines, but the fat-line animals had greater fat depths at C and to a lesser extent at J, S2, LG and L2. Tissue depth GR was also significantly greater in the fat line. Comparisons at the same weight showed that sides from the meaty line contained more muscle and bone with less fat than those from the fat line, but the meaty-line carcasses had a relatively lower dressing-out percent. Carcass length was significantly longer for the meaty-line than the fat-line animals, but the maximum width behind the shoulder was greater for the fat line. The length of leg and several bones (femur, humerus, radius, and tibia and fibula) were greater for the meaty line than the fat line. With the exception of the higher rack cut percent in the fat line, the two selection lines did not differ in the weight distribution among the shoulder, loin, and leg cuts within the side, or in the distribution of muscle, bone and fat weights. When adjusted to the same side fat weight, the side from the fat line contained more subcutaneous fat, more intramuscular fat, and less intermuscular fat. Based on succinic dehydrogenase staining procedures, M. semitendinosus from the fat line was found to have a significantly higher percent of red muscle fibre (βR) and a correspondingly lower percent of intermediate (αR) and white muscle fibre (αW). No significant line differences were observed for the diameter of the three muscle-fibre types. For five adipose tissue depots (subcutaneous, intermuscular, kidney, omental and mesenteric) adipocyte size was greater for the fat line. In addition, the subcutaneous fat depot of fat-line sheep contained significantly more cells in one of the three experiments. Equations relating side fat percent with fat percent of the rack cut (8 to 12 rib) differed significantly between the two lines with regard to intercept. This effect appeared to be due to the small overlap in fat percent values for the two lines. Selection line differences in indices of meat quality (Warner-Bratzler shear force, sarcomere length, reflectance, expressed juice, cooking loss and pH) for four muscles (Mm. longissimus, biceps femoris, semitendinous, semimembranosus) were generally small and non-significant. Meat from animals of the two selection lines did not differ significantly in the extent to which shear values decreased in response to electrical stimulation, to ageing for 15 days (M. semimembranosus), to the removal of cold-shortening conditions (M. biceps femoris), or to not trimming the subcutaneous fat over the M. longissimus. However, the shear force values and sarcomere lengths from both lines were significantly affected by all of these post-mortem treatments.
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    Investigations into muscularity as a characteristic of sheep carcasses at various stages of growth : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, New Zealand
    (Massey University, 1994) Abdullah, Abdullah Yousef; Abdullah, Abdullah Yousef
    Muscularity is a meat animal characteristic defined as the depth of muscle relative to skeletal dimensions. It is usually assessed subjectively, but a possible objective measure involves obtaining an average muscle depth by taking the square root of the weight per unit length of muscles around the femur, and expressing this relative to femur length. A series of experiments was conducted to assess this objective measure of muscularity (MUSC), and the value of muscularity as a meat production trait. These involved evaluation of first, the pattern of change in MUSC with growth of sheep from birth to near maturity, secondly, relationships between MUSC in different parts of the carcass, thirdly, relationships between MUSC and muscle fibre size and number, fourthly, breed differences in MUSC, fifthly, relationships between MUSC measured objectively and subjectively, and finally, indirect predictors of MUSC based on simple measurements. Southdown rams from lines selected for high- or low-backfat depths (n=40 per line) were studied at birth, 10, 20, 40, 60, and 80 kg liveweight and at near maturity. Muscularity and M:B ratios from different groups of muscles and bones, together with other indexes of carcass shape, including the depth to width ratio of a transverse section of M.longissimus and a carcass weight to length ratio (CWT:L3), increased at a decreasing rate with increasing carcass weight. For most ratios this increase was parallel for both lines with the high-backfat line having higher values, but for muscularity in the femur region the differences between the lines increased with growth. Muscularity based on the muscles around the femur showed line differences most clearly. Line differences in muscularity did not appear to be associated with consistent differences in bone shape. Proportions of muscle fibre types in the M.semitendinosus were generally similar for the two selection lines. Data from 211 carcasses from 4 trials were evaluated to study differences between breed and sex groups of sheep in the pattern of change in muscularity with increasing carcass weight. Leg muscularity increased for all groups with increasing carcass weight, and the rate of increase was similar at carcass weights above 10 kg. The Southdown breed had higher muscularity values and M:B ratios than Texel crosses, which in turn had higher values than all other groups. For some comparisons, there were important sex effects. At a similar carcass weight, Coopworth rams had slightly higher muscularity values (+1.7%; P<0.10), but lower M:B values (-8.8%; P<0.001) than Poll Dorset-cross cryptorchids. Relationships between objective measures of muscling and subjective scores of muscularity or conformation were studied using data from 95 lambs and 90 bulls. Muscularity calculated from the leg cut rather than whole side or eye-muscle dimensions had the closest relationships with subjective scores of muscularity or conformation (R2% = 69 to 80% for lambs and 56% for bulls), with leg M:B being only slightly inferior (R2% = 62% for lambs and 52% for bulls). Muscularity and M:B ratio calculated from the side were the next best as predictors, but variables based on the eye muscle were poor. Data from 5 trials were used to examine indirect objective methods to predict leg muscularity for sheep carcasses. Muscularities based on M.semimembranosus or M.biceps femoris were accurate predictors when compared with indexes based on other individual muscles. Muscularities based on the topside and outside commercial boneless cuts were also good predictors. Indexes of muscularity calculated from carcass linear and eye-muscle dimensions were poor as predictors. Leg width to length (W/L) ratios obtained from lateral leg photographs proved useful as predictors. Individual W/L values or groups of W/L values combined as bands were moderately effective as predictors for some trials. However, the regression prediction equations varied between trials. It is concluded that the objective measure of carcass muscularity investigated here is a carcass characteristic that reflects important differences in carcass shape, and that differences in this characteristic between carcasses are not necessarily accompanied by corresponding changes in muscle to bone ratio.