Massey Documents by Type

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

Browse

Has files: YesSubject: search.filters.subject.Texel sheep

Search Results

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Investigation into the inheritance and biochemistry of chondrodysplasia in Texel sheep : a thesis presented in partial fulfilment of the requirements for the Master of Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2005) Byrne, Timothy John
    A skeletal chondrodysplasia characterized by dwarfism and angular deformity of the forelimbs has been recognized over four seasons in Texel and Texel cross lambs on three related properties. Some affected lambs have normal co-twins indicating that the disease is not dietary, but likely to be the result of a genetic disorder. This study reports on the inheritance and biochemistry of this newly discovered chondrodysplasia in Texel sheep. The outcome of a backcross trial between putative carrier ewes and affected rams provided evidence that indicated that the chondrodysplasia has an autosomal recessive mode of inheritance, and that it is likely to be caused by a single gene defect. Analysis of proteoglycan constituents of cartilage by SDS-PAGE, followed by sulfate-specific staining indicated that the biochemical abnormality lies in the level of sulfation of proteoglycans in the extracellular matrix of affected animals. It was also shown by SDS-PAGE that there were no differences in the major collagen constituents of cartilage between unaffected and affected animals. A candidate gene, the diastrophic dysplasia sulfate transporter, was determined based on its involvement in the process of sulfation of proteoglycans and its involvement in characterized human dysplasias, which resemble Texel chondrodysplasia both phenotypically and biochemically. PCR amplification and sequencing of 85.4 % of this gene revealed no nucleotide differences between the exonic DNA of normal, carrier, and affected animals. While this reduced the likelihood that this gene is causative in the chondrodysplasia, it does not eliminate it as a candidate, based on the fact that a mutation may exist in the region not sequenced, including the possibility of splice site mutations.
  • Thumbnail Image
    Item
    A study of commercial embryo transfer programmes conducted with Texel and Awassi sheep : a thesis presented in partial fulfilment of the degree of Master of Agricultural Science in Animal Science at Massey University
    (Massey University, 1997) Pavitt, Andrew Edward Drummond
    The results of two commercial embryo transfer (ET) programmes conducted in Central Huwkes Bay, comprising 93 Texel and 78 Awassi donor ewes, were analysed to identify variables that affect the success of commercial ET programmes. The production of high quality embryos for export was the primary objective in the Texel programme, while the rapid multiplication of the Awassi was the sole purpose of the Awassi programme. Reproductive parameters such as; ovarian response to exogenous gonadotrophins, recovery and fertilisation rate of ova, yield of good quality embryos and embryo survival rate to scanning and birth were evaluated. The influence of age, ovulatory response, repeated flushing, the number of corpora lutea in recipient ewes and donor surgeon, on the reproductive parameters, were assessed. The Texel ewes were all purebred consisting of two-tooth and four-tooth animals. The Awassi ewes were either three-quarter or purebred, and included both ewe hoggets and mixed age ewes. Synchronisation of oestrus was attempted using a double CIDR-GTM regime. The super ovulatory programme differed in each breed but consisted of a series of FSHp injections in combination with PMSG. The ewes were inseminated intra-uterine with fresh diluted semen from a ram of the same breed after detection of oestrus. Embryo recovery was attempted 6-6.5 days after insemination using a standard flushing technique in which the oviducts and uterus were exposed by mid-ventral laparotomy. Two or three embryos were transferred into each recipient ewe within 1.5 hours (Texel) and 4 hours (Awassi) of recovery. Ovarian response to superovulatory treatment was not significantly affected by any of the variables recorded in this study, although the Texel programme provided a higher ovulatory response than the Awassi programme (8.89 CL vs 7.08 CL). The embryo recovery rates were 71.8% for the Texel and 78.1% for the Awassi sheep. Age of the donor ewes significantly affected (p=0.006) recovery rate of ova in the Awassi sheep, adult ewes and ewe hoggets recorded recovery rates of 90.7% and 65.2%. Fertilisation rate was not affected by any of the factors studied with 94.6% and 77.6%, of ihe Texel and Awassi ova, being fertilised. The overall yield of good quality embryos was 91.6% for the Texel and 80.1% for the Awassi. The yield of good quality embryos was significantly affected (p=0.03) by age in the Awassi, 87.5% of adult embryos and 64.4% of ewe hogget embryos were of good quality. Survival rates in the Awassi data set were significantly affected by the lower scanning and birth rates of the Awassi ewe hoggets than Awassi ewes (43.8% vs 65.9%: p=0.02) and (39.3% vs 59.4%: p=0.03) respectively. Each Texel donor ewe produced, on average, 3.89 embryos that were of sufficient quality to be preserved and therefore not transferred, resulting in 0.70 lambs being born per donor ewe in the Texel programme. The Awassi programme produced 2.10 lambs donor per ewe, however, this was significantly affected (p=0.03) by the age of the donor ewes, with adult ewes produced an average of 2.7 lambs per donor, and ewe hoggets, 1.2 lambs per donor. This work demonstrated the variable nature of embryo transfer programmes as well as the difficulty in achieving acceptable results from ewe hoggets. The Texel and adult Awassi results compared favourably to the other published reports and illustrate that on-farm commercial embryo transfer can provide acceptable results.
  • Thumbnail Image
    Item
    A directed search for QTL affecting carcass composition traits in Texel sheep : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2003) Johnson, Patricia Lea
    In New Zealand moves towards lean-meat yield- and meat quality-based payment of lamb carcasses, which more accurately reflect consumer preferences, mean that breeders and producers will need to change their selection objectives and management practices to maximise returns. This thesis investigates approaches to achieving increased meat yields, while not detrimentally affecting meat quality. The main objective was to search for Quantitative Trait Loci (QTL) affecting carcass composition traits in Texel sheep, in the region of Growth Differentiation Factor 8 (GDF8) on ovine chromosome 2. Dissection and meat quality data for legs and loins were collected for 90 Texel-cross progeny from each of six Texel or Texel-cross sires. All animals were genotyped for seven markers around GDF8. A QTL which increased leg muscle by 5-8% and decreased leg fat by 10-15% was identified for four of the six sires in the region of markers BM81124 and BULGE20. The two sires for which no QTL was detected, were homozygous and therefore uninformative at these markers. The QTL did not negatively affect meat quality. There was only limited evidence for a QTL affecting loin composition traits. Candidate genes to explain the QTL effect, in addition to GDF8, were sought, based on the conserved synteny between the ovine and human genomes, but none were identified. A number of genes in the region are poorly documented, and new genes are still being mapped to the region so a candidate gene could yet emerge. The progeny data set when analysed for sex differences, revealed that, relative to ewe lambs, meat from the ram lambs had 10% higher Warner-Bratzler shear values, was less red, and for M. longissimus, had 28% more samples that exceeded the "high pH" threshold of 5.8. These negative meat quality aspects for ram lambs need further investigation to determine their commercial importance. Future research on the putative QTL for leg and loin composition should assess its effects on other parts of the carcass, and its effect in lambs homozygous for the QTL. Additionally its position needs to be more closely defined, and ideally the specific gene or genes involved identified, before industry implementation is carried out.
  • Thumbnail Image
    Item
    Chondrodysplasia of Texel sheep : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy at Massey University, Palmerston North, New Zealand
    (Massey University, 2008) Piripi, Susan Amanda
    Chondrodysplasia of Texel sheep is a newly described recessively inherited disorder distinct from other chondrodysplasias described in sheep. Phenotypically normal at birth, affected lambs develop microscopic lesions as early as 9 days of age, and usually demonstrate gross deformities and markedly reduced rates of bone growth by 2 to 3 weeks. Individual bone growth rates are most severely affected in the proximal bones of the forelimbs. Chondrodysplastic lambs typically have short stature, angular limb deformities, a barrel-shaped chest and a wide-based stance. Gross lesions include tracheal narrowing and contortion, enlarged costochondral junctions, and erosion of articular cartilage in major limb joints. Microscopic lesions are confined to hyaline cartilage, and are characterised by degeneration of the interterritorial matrix and dense perichondrocytic rings consisting predominantly of type VI collagen. These lesions are identical in appearance to those in achondrogenesis 1b and diastrophic dysplasia, two diseases caused by defects of the diastrophic dysplasia sulphate transporter (DTDST) in human beings. An investigation to measure the uptake of radiolabelled sulphate by dermal fibroblasts in vitro did not provide evidence of a defect in the DTDST in chondrodysplastic Texel sheep. A linkage disequilibrium study of ovine chromosomes 1, 5, 6, 13 and 22 using microsatellite DNA markers was unable to identify evidence of a mutation causing this form of chondrodysplasia. Capillary electrophoresis of unsaturated chondroitin sulphate disaccharides demonstrated a relative reduction in the ratio of chondroitin 4-sulphate to chondroitin 6-sulphate in affected animals of all ages. This biochemical feature enables the potential determination of the phenotype of newborn lambs prior to the emergence of gross or microscopic lesions. The pathology of the disease, combined with the findings of the genetic, biochemical and in vitro studies, suggest that a mutation may be present in the CHST11 gene. This gene is a good candidate for future studies aimed at discovering the genetic defect in chondrodysplasia of Texel sheep and developing a test to identify heterozygous animals.