Massey Documents by Type

Permanent URI for this communityhttps://mro.massey.ac.nz/handle/10179/294

Browse

Subject: search.filters.subject.Southdown sheep

Search Results

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    Direct and correlated responses to selection for high or low ultrasonic backfat depth in Southdown sheep : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Animal Science at Massey University
    (Massey University, 1988) Ramirez, Jose Solis
    Divergent selection was employed to establish high and low lines for liveweight-adjusted backfat depth (LABF) assessed ultrasonically in Southdown sheep. The selection lines were initially constituted from several sources with stock brought-in during the first three years of the experiment (1976-1978). These first years were used to evaluate ultrasonic equipment for measuring backfat depth. The lines were closed in 1979. Data analysed in this study were collected over 8 years (1979-1986) representing, approximately 2.66 generations. Selection was practised in two stages, with a preliminary selection based on the first LABF on the rams and ewes, and a final selection based on an average of all measurements assessed throughout the year for the rams only. Direct selection for high or low backfat depth resulted in the 1986 born animals in the high line having about 1.69mm (59.6%DEV) and 2.00mm (49.57%DEV) thicker backfat than the low line in the rams and the ewes, respectively. The responses to selection per unit of cumulated selection differential were in most cases high. Due to prior selection and difficulties in assessing the selection pressure, it was concluded that these regressions poorly represented the selection process. Correlated responses to selection for and against backfat depth were generally small. However, consistent positive correlated response were observed in liveweight-adjusted height and length (LAH and LAL) over the selection period. These responses imply a negative genetic correlation between these traits and backfat depth . This finding was in agreement with the published literature. Phenotypic correlations were calculated within-trait between-days and between-traits within-days. Correlations were pooled within-trait following tests of homogeneity. The within trait values were generally moderate to high and they were in agreement with the values reported in the literature. The between-traits correlation values were generally low, but were consistently negative for LABF-LAH and LABF-LAL, and consistently positive for LAL-LAH . Repeatability estimates, using the within-trait combinations, were also in agreement with the literature and suggested a moderate to high repeatability for LABF and LAH. Repeatability estimates for LAL were low to moderate and they were slightly smaller than the values reported in the literature. Estimates of the heritability of LABF varied with method used. The paternal half-sib method resulted in low values (0.14 to 0.19) while dam/offspring method gave moderate values (0.29 to 0.43) . Corresponding heritability estimates for LAH and LAL were about 0.31 and -0.14, respectively. These values were smaller than other results quoted in the literature. It was concluded that truncation selection on LABF reduced the genetic variability of these traits, although not to the same extent as for LABF. It was concluded that divergent selection for LABF was effective, resulting in lines with significantly different backfat depth at the same liveweight. Furthermore, selection for low LABF led to significantly longer and taller animals.
  • Thumbnail Image
    Item
    A study of metabolic differences between fat and meaty Southdown sheep : a thesis presented in partial fulfillment of the requirements for the degree of Master of Agricultural Science in Animal Science at Massey University
    (Massey University, 1987) Carter, Mark Levett
    The level of fatness in sheep meats is a key factor taken into account by consumers at all levels. With pricing structures offered to producers now starting to reflect this demand, there is a need for an increased understanding of the factors which affect the composition of growth so that the producer will be able to more efficiently adjust the growth patterns of young animals. The basic objective in the long term is to develop an animal which grows an increased proportion of lean tissue more efficiently (Simm and Smith 1984) . Selection of lean growing animals by existing methods of body composition estimation is hampered by low correlations with true composition. The identification of metabolic markers of genetic merit for lean meat production is being attempted in the hope that these markers will improve the potential rate of genetic gain. [From introduction.]
  • Thumbnail Image
    Item
    A study of the metabolism of low and high backfat Southdown sheep at two levels of energy allowance : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Animal Science at Massey University
    (Massey University, 1989) Morgan, Peter Francis
    The New Zealand meat industry requires that producers supply lean animals for slaughter and, accordingly, payments are structured such that excessive carcase fat is heavily penalized. This requirement is a consequence of the increasing consumer preference for lean meat of high quality, a trend which reflects medical evidence that high fat diets are unhealthy, particularly given modern sedentary lifestyles. Moreover, the modern consumer prefers products which require minimal preparation and contain little waste. Selection for lean growth has therefore become an increasingly important component of sheep selection programmes. The rate of genetic gain in these programmes is to a large degree dependent upon the ability of breeders to identify animals of high genetic merit.
  • Thumbnail Image
    Item
    Some composition characteristics of young male Southdown sheep from lines selected for high and low backfat depth : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Animal Science at Massey University
    (Massey University, 1989) Abdullah, Abdullah Yousef
    Thirty-six 6-8 month Southdown ram lambs, 18 each from the high and low-backfat selection lines established at Massey University in 1976, were used in this study to evaluate some carcass composition characteristics. Animals were randomly allocated within lines within sire groups into three lots of 12 rams each and were housed in metabolism crates on a lucerne chaff diet (1.3 maintenance). After a 10-day adjustment period, an intravenous urea challenge was administered to the animals (120 mg/kg LW) and blood samples were collected before and after the infusion. Rams were slaughtered within 5-7 days of the urea challenge and half-carcasses were separated into soft-tissue and bone. Differences in body composition between the selection lines were greatest for measures of fatness. They were found to a lesser extent in some other characteristics, especially those that have been reported previously to have positive or negative genetic correlations with backfat depth. Thus, carcasses from the high-backfat line, when compared at the same carcass weights had significantly greater fat depths at C, J, GR, S2 and L3, by 56.7%, 37.1%, 26.1%, 33.3% and 51%, respectively. The high-backfat line group also had significantly greater amounts of kidney fat, higher chemically analysed fat percentage in the carcass soft-tissue, larger intermuscular fat cell diameter, shorter carcasses, lighter heart and liver weights, deeper (B) and narrower (A) cross sections of M. longissimus, and slightly higher (P<0.10) dressing-out percentages. Moreover, at the same carcass weight, the results of the current study agree well with previous studies in showing that fatter lambs had a higher proportion of the fatter cuts (rack cuts) and a lower proportion of the leaner cuts (shoulder cuts). The high-backfat line animals also had lighter total side bone weight, and shorter lengths and smaller circumferences of the humerus, radius & ulna, femur and tibia bones in the carcasses, which agrees with the negative genetic or phenotypic correlations reported elsewhere between backfat thickness and bone weight, bone percentage or bone length in sheep. At the same total side bone weight, line effects on bone distribution in the current study were less marked than the previous work with 17-month-old rams, with significantly higher weights of bone in the rack cut, lower weights of bone in the leg cut and lighter humerus and femur bone weights for the carcasses of the high-backfat line. Shoulder cut bone weight in the present study did not differ between selection lines and the difference was in the opposite direction for the total leg bone cut compared with older rams in the previous study. At the same carcass weight, similar total weight of four muscle in the carcasses of both lines was found, but at the same fat-free soft tissue weight in the side there are few effect on the distribution of muscle. The ratio of muscle to bone weight and muscularity are higher in the high-backfat line when adjusted to the same fat-free soft tissue and total side fat-free soft tissue weight plus bone respectively. These results are consistent with previous studies in showing that the reduction in backfat thickness have little or no effect on total muscle weight, little effect on muscle distribution and lower ratio of muscle to bone weight and lower muscularity. Line differences in muscle fibre type, proportion and area in the M. semitendinosus were not found in the present study. This result which differs from previous which showed higher proportions of (ßR) red fibres for the high-backfat line. In general, all moisture measurements showed a slightly higher weight and percentage in the low-backfat line. The prediction of empty body water percentage from the response to a urea challenge by measuring the rate of urea dilution in the plasma was not very successful. The best extrapolation estimates of zero-time were obtained using a simple exponential model after linear adjustments were made for increasing baseline values. It is concluded that divergent selection for and against fatness on the basis of weight-adjusted ultrasonically-measured fat depth C in the present lines has led to line differences in 14 kg carcasses such that the fat line carcasses have more fat, less bone and a similar weight of muscle. The urea dilution method as used in this study was found to be unsatisfactory for the prediction of carcass composition.
  • Thumbnail Image
    Item
    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.