Poll Dorset Sheep Research Articles

Genetic analysis of weight, fat and muscle depth in growing lambs using random regression models

AbstractGenetic parameters were estimated using uni- and bi-variate random regression models for weight, eye-muscle depth and fat depth measures between 60 and 360 days of age. Each trait was measured up to five times in 50-day intervals following weaning on approximately 4000 Australian Poll Dorset Sheep. The model accounted for rearing type, dam age, management group and age of recording. The model used for analysing weight included quadratic, orthogonal polynomials for direct genetic and environmental effects, a linear polynomial for maternal genetic effects and heterogeneous error variance across ages. The fat and muscle analysis used linear orthogonal polynomials for direct genetic and environmental effects and heterogeneous error variance. Throughout the 300-day trajectory heritability for weight traits ranged from 0·20 to 0·31, while heritability for fat depth ranged from 0·24 to 0·34 and heritability for eye-muscle depth ranged from 0·24 to 0·40. Genetic correlations between repeated measures of the same trait at different ages were positive and declined as the age interval increased, to minimum values of 0·60, 0·31 and 0·50 for weight, fat and muscle respectively between 60 and 360 days of age. Genetic correlations between weight and fat and weight and eye muscle were moderate to high (0·6 to 0·8) and positive but decreased slightly with age. The genetic correlations between fat and muscle were moderate to high (0·5 to 0·7) throughout the 300-day trajectory. In all cases, the estimates produced in this study were reasonably consistent with the limited number of studies that exist in the reported literature. This study demonstrated the relationships that exist between repeated measures of weight, fat and muscle measures over time, which is of interest to prime lamb producers looking to select for specific breeding objectives or market end points requiring precise weight, fat and muscle combinations at certain ages.

Description of lamb growth using random regression on field data

Random regression has been proposed as an accurate method for evaluation of growth data; however, this method has seldom been applied to data from an extensive industry where few records per animal exist. Consequently, field data containing weights of Poll Dorset sheep from 50 to 500 days of age were analysed fitting a random regression model. This model included quadratic, orthogonal polynomials for direct genetic and environmental effects and maternal environmental effects, a linear polynomial for maternal genetic effects and heterogeneous error variances. Direct heritability estimates increased steadily throughout time and were in agreement with literature estimates taken at specific ages. Some estimates for the highest ages with the least records tended to be overestimated, in particular heritability beyond 450 days. Research to solve this problem may require use of a function other than a polynomial. Variances due to maternal genetic effects were low throughout the trajectory. Covariances between weights of sheep for a considerable range of ages can be modelled adequately using random regression.

Vacuolar Lesion Profile in Sheep Scrapie: Factors Influencing its Variation and Relationship to Disease-specific PrP Accumulation

Detailed neuropathological examination for vacuolar lesions was performed on the brains of 42 sheep with clinical signs compatible with scrapie. The sheep were grouped according to their breed (Poll-Dorset, Cheviot, Welsh Mountain, Shetland and Suffolk), their PrP genotype at codons 136, 154 and 171 (VRQ/VRQ, VRQ/ARQ, VRQ/ARR and ARQ/ARQ) and the type of infection (experimental infection with SSBP/1, or natural disease). Twenty-two neuroanatomical sites from seven brain regions were examined for vacuolation in the neuropil and five sites at the level of the obex were examined for intraneuronal vacuolation. In 36 sheep, immunohistochemical examination for disease-specific PrP (PrP d) accumulation had also been performed in the same brain regions in an earlier study. The magnitude of total neuropil vacuolation was highest in the naturally affected ARQ/ARQ Suffolk sheep and lowest in the experimentally infected VRQ/VRQ Cheviot sheep and VRQ/ARR Poll-Dorset sheep. The severity of neuropil vacuolation at nine of the 22 neuroanatomical sites examined was used to generate a vacuolar lesion profile, which showed variations between the different sheep groups. These variations could be attributed to both PrP genotype and sheep breed and also possibly to scrapie agent; there was, however, considerable individual variation in lesion profile within sheep groups. All groups showed a similar ratio of neuropil vacuolation to neuronal vacuolation at the level of the obex. Although a positive correlation between neuropil vacuolation and PrP d deposition was generally observed, it was low except for the astrocyte-associated pattern of PrP d accumulation. The study suggests that vacuolar lesion profiles in sheep are affected by several factors and, by comparison with lesion profiles in mice, are of no more than limited value for discriminating between scrapie strains.

Bluetongue virus serotypes 1 and 3 infection in Poll Dorset sheep.

To study the clinical signs following bluetongue virus serotypes 1 and 3 infection in Poll Dorset sheep. A clinical and pathological study. Twenty Poll Dorset sheep were inoculated with bluetongue virus serotypes 1 or 3, each inoculum having a different passage history. The sheep were examined daily and their clinical appearance and rectal temperatures recorded. Heparinised and non-heparinised blood samples were taken at intervals for virological and serological study. Gross pathological findings were recorded for several sheep at necropsy and tissue samples were collected from three sheep for virological studies. All inoculated sheep developed clinical disease. The clinical signs and gross pathological changes varied considerably but were consistent with damage to the vascular endothelial system. There was a decline in the titres of infectious bluetongue virus and of antigen in tissues collected between 7 and 12 days after infection. The severity of disease was related to the speed of onset and duration of pyrexia and not the development or titre of viraemia. Generally, those animals with sensitive mouths, depression, coronitis, recumbency and reluctance to move were the most debilitated. Whole blood was the most reliable source of infectious virus from acutely and chronically infected and convalescent animals. However, tissue samples particularly spleen, collected from dead or killed animals suffering from either peracute or acute forms of disease were most appropriate for the rapid confirmation of a clinical diagnosis.

Scrapie-free Merino and Poll Dorset sheep from Australia and New Zealand have normal frequencies of scrapie-susceptible PrP genotypes.

As natural scrapie occurs only in sheep of specific PrP genotypes, one proposed aetiology was that scrapie is simply a genetic disease. However, Cheviot and Suffolk sheep of scrapie-susceptible genotypes are found in Australia and New Zealand, both generally accepted to be scrapie-free countries. A study of more common Australia and New Zealand sheep breeds (Merinos and Poll Dorsets) was carried out in order to obtain more generally applicable estimates of Australia and New Zealand sheep PrP genotype frequencies. We have confirmed that animals of highly susceptible PrP genotypes are found in Australia and New Zealand. Interestingly, the Poll Dorset sheep, although born in New Zealand, were brought to the UK as young adult animals and subsequently remained free of clinical scrapie despite 21% of the sheep having scrapie-susceptible genotypes. These results have implications for the genetic control of occurrence of the equivalent human diseases.

Congenital hypotrichosis in Poll Dorset sheep.

Australian Veterinary JournalVolume 69, Issue 6 p. 146-147 Congenital hypotrichosis in Poll Dorset sheep JT MACKIE, JT MACKIE Department of Agriculture, Regional Veterinary Laboratory, PO Box 388, Benalla, Victoria 3672Search for more papers by this authorB McINTYRE, B McINTYRE Benalla Veterinary Clinic, 16 Church Street, Benalla, Victoria 3672Search for more papers by this author JT MACKIE, JT MACKIE Department of Agriculture, Regional Veterinary Laboratory, PO Box 388, Benalla, Victoria 3672Search for more papers by this authorB McINTYRE, B McINTYRE Benalla Veterinary Clinic, 16 Church Street, Benalla, Victoria 3672Search for more papers by this author First published: June 1992 https://doi.org/10.1111/j.1751-0813.1992.tb07490.xCitations: 6AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume69, Issue6June 1992Pages 146-147 RelatedInformation

Genetic variation in liveweight and ultrasonic fat depth in Australian Poll Dorset sheep

Genetic and phenotypic variances and covariances were estimated for liveweight and ultrasonic fat depth in the Australian Poll Dorset. The data were obtained from the New South Wales Meatsheep Testing Service between 1983 and 1986, and involved 28 159 records from 50 stud flocks. A total of 681 sires were used to derive the half-sib genetic parameters. The data were further grouped according to average age at measurement, so that parameters were estimated for animals within age ranges of 4-6 months, 7-11 months and 12-16 months. Heritabilities for liveweight were between 0.21 and 0.31, with the highest value obtained in the oldest age group. Heritabilities for fat depth varied between 0.26 and 0.31, with the highest value again obtained in the oldest age group. Genetic correlations between liveweight and fat depth were about 0.4 except in 4-6-month-old animals where the estimate was about 0.7. The implications of these parameters to breed improvement programmes are discussed. In particular, the scope for genetic response in producing faster growing, leaner animals at a constant liveweight is highlighted. Information on sire-son generation intervals and apparently limited between-flock genetic variation is reported. The results indicate the need to improve the evaluation procedures for sires within the breed at both the between- and within-flock level.

Genetic distance between the Australian Merino and the Poll Dorset Sheep

SUMMARYMerinos (189) and Poll Dorsets (106) were compared for genetic variation at 30 loci for blood proteins. ‘Malic enzyme’ and NADH diaphorase I polymorphism occur in Merinos but not in Poll Dorsets, whereas both breeds are polymorphic for haemoglobin, erythrocyte X-protein, serum esterase, catalase and transferrin, although the breeds differ in the presence or absence of certain rare transferrin variants. Poll Dorsets but not Merinos have genetic variation of erythrocyte pyruvate kinase at low gene frequencies; Merinos but not Poll Dorsets have genetic variation of two erythrocyte Gly-Leu peptidases, glucosephosphate isomerase, superoxide dismutase, and NADH diaphorase II, all at low gene frequencies (P< 0·05).Using Masatoshi Nei's (1972, 1976) standard genetic distance, over all 30 loci, to calculate the time of divergence of the two breeds, we obtainedt= 69700 years – whereas sheep are believed to have been domesticated by man for not more than 11000 years, and ancestors of the British breeds and of the Merino have probably not been separated for more than 2000 years. Several possible explanations for this discrepancy are discussed, including the accuracy of the coefficient of codon change (α), changes in population size and structure, selection, and additional hybridization in the ancestry of the Merino.

A Viable Hypotrichosis in Poll Dorset Sheep

Journal Article A Viable Hypotrichosis in Poll Dorset Sheep Get access C. H. S. DOLLING, C. H. S. DOLLING The authors are affiliated with the Division of Animal Genetics, Commonwealth Scientific and Industrial Research Organization, National Field Station“Gilruth Plains”, Cunnamulla, Queensland Australia Search for other works by this author on: Oxford Academic PubMed Google Scholar M. G. BROOKER M. G. BROOKER The authors are affiliated with the Division of Animal Genetics, Commonwealth Scientific and Industrial Research Organization, National Field Station“Gilruth Plains”, Cunnamulla, Queensland Australia Search for other works by this author on: Oxford Academic PubMed Google Scholar Journal of Heredity, Volume 57, Issue 3, May 1966, Pages 87–90, https://doi.org/10.1093/oxfordjournals.jhered.a107482 Published: 01 May 1966