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Biomedical subjects

P D Johnstone

Publications and source records attributed to P D Johnstone.

At least 19 recordsLinked to original sources
PubMed2003

Bone density in sheep: genetic variation and quantitative trait loci localisation.

Bone density (BD) is an important factor in osteoporotic fracture risk in humans. However, BD is a complex trait confounded by environmental influences and polygenic inheritance. Sheep provide a potentially useful model for studying differences in BD, as they provide a means of circumventing complex environmental factors and are a similar weight to humans. The aims of this study were to establish whether there is genetic variation in BD in sheep and then to localise quantitative trait loci (QTLs) associated with this variation. We also aimed to evaluate the relationship between fat and muscle body components and BD in sheep. Results showed that there was significant (P < 0.01) genetic variation among Coopworth sheep sires for BD. This genetic difference was correlated (P < 0.01) with body weight and muscle mass. A number of QTLs exceeding the suggestive threshold were identified (nine in total). Of these, two (chromosomes 1, P < 0.05; chromosome 24, P < 0.01) were significant using genome-wide permutation significance thresholds (2000 iterations). The position of the QTL on chromosome 24 coincided with a number of other body composition QTLs, indicating possible pleiotropic effects or the presence of multiple genes affecting body composition at that site. This study shows that sheep are potentially a useful model for studying the genetics of BD.

Animals↗
PubMed2001

Factors affecting parasitism by Microctonus aethiopoides (Hymenoptera: Braconidae) and parasitoid development in natural and novel host species.

A laboratory study of aspects of parasitoid host acceptance, suitability and physiological regulation in natural and novel host species was carried out to investigate the degree of variability encountered with different hosts and to determine the value of such observations in host range determination. The parasitoid Microctonus aethiopoides Loan was exposed to a natural host, Sitona discoideus Gyllenhal (Coleoptera: Curculionidae) and three novel hosts, the New Zealand native Nicaeana cervina Broun, the introduced weed biological control agent Rhinocyllus conicus (Froehlich), and a congeneric pest species, Sitona lepidus Gyllenhal (all Coleoptera: Curculionidae). Per cent parasitism of these species was 54%, 43%, 39% and 0%, respectively. The results indicated that for both S. discoideus and R. conicus more males than females were parasitized (69% cf. 45%, and 49% cf. 32% respectively) but host size was not a significant factor. Overall, superparasitism was recorded in about 29% of parasitized weevils and there was evidence that host discrimination to avoid superparasitism occurred in the natural host. Conversely, superparasitism occurred more frequently than would be expected in N. cervina (42%) coupled with higher survival of larvae in superparasitized hosts in this species. The frequency distribution of attack of R. conicus by M. aethiopoides was not different from random. Parasitoid development was more rapid in the natural host, S. discoideus, and parasitoid size was positively correlated with host size. There was a strong positive relationship between parasitoid larval survival and the presence of teratocytes in all hosts. Host fecundity and fertility were reduced by parasitism for most species, and in some cases, by exposure to parasitoids in the absence of detectable parasitism. It was concluded that laboratory observations can provide useful information on the compatibility between host and parasitoid which can complement traditional host range tests to predict field host range.

Animals↗
PubMed1998

Interpreting comparative experiments on parasite burdens in animals using randomization and canonical variates.

Comparative experiments on parasite burdens present difficulties for modelling and interpretation: data tend to have highly skewed distributions, some standard methods of testing for effects have low power, and there is a need to make allowance for dependencies among the various measurements. Randomization testing and canonical variates analysis are advocated as a means of minimising these problems.

Abomasum↗
PubMed1998

The efficacy of a pour-on formulation of moxidectin in young red and wapiti-hybrid deer.

AIMS: To measure the efficacy of a pour-on formulation of moxidectin against lungworm and abomasal parasites in weaner wapiti x red deer and to compare this with its efficacy in weaner red deer. METHODS: Six red and six wapiti hybrid deer, naturally infected with lungworm and gastro-intestinal parasites, were treated with pour-on moxidectin at 500 microg/kg body weight and slaughtered 14 or 16 days later, along with six red and six wapiti hybrid untreated control deer. Total worm counts were performed on the lungs, abomasum and abomasal digest of each deer. RESULTS: The efficacy of moxidectin pour-on was 100% against adult and immature lungworms (Dictyocaulus viviparus) in red deer, and 100% and 99.7% effective against adult and immature lungworm in wapiti hybrid deer. The efficacy of moxidectin pour-on was 100, 100, 99.9 and 99.9% respectively against adult, fifth stage, late fourth stage and early fourth stage larvae of Ostertagia-type nematodes (assumed to be Ostertagia, Spiculopteragia, Skrjabinagia and Apteragia spp.) in both red and wapiti hybrid deer. CONCLUSIONS: The pour-on formulation of moxidectin, at 500 microg/kg body weight, is highly effective against mature and immature lungworms and abomasal nematodes in wapiti hybrid deer and equally effective in red deer.

Journal Article↗
PubMed1997

Identifying infertile homozygous Inverdale (FecXI) ewe lambs on the basis of genotype differences in reproductive hormone concentrations.

Introduction of the Inverdale prolificacy gene (FecXI) could markedly improve reproductive efficiency in commercial flocks, but as homozygous carrier Inverdale ewes are infertile, it is imperative that these animals are identified at an early age and excluded from breeding stock. As the ovaries of homozygous carrier ewes are nonfunctional, there are wide differences in reproductive hormone levels between these and other Inverdale genotypes. This study assesses the accuracy of using hormone concentrations alone, to identify infertile homozygous ewe lambs. Ewe lambs were blood sampled at 2, 5 and/or 8 months of age, and plasma analyzed for follicle-stimulating hormone (FSH), luteinizing hormone (LH) and inhibin content. These animals were either the offspring of both known carrier rams and known carrier ewes, and therefore would be either homozygous (II) or heterozygous (I+) for the Inverdale gene (group 1, N = 122), or had one parent that was a carrier and therefore would be either heterozygous or noncarriers (++) of the gene (group 2, N = 32). Animals were designated as either II or I+/++ on the basis of their plasma hormone concentrations. Inverdale genotype was also assigned from laparoscopic observation of the ovaries at each of these occasions. Definitive assignment of genotype was made at laparoscopy as adults during the breeding season. On the basis of laparoscopy as adults, 62 (51%) lambs in group 1 were identified as homozygous and 60 (49%) as heterozygous. At all three ages, both mean FSH and mean LH concentrations were significantly higher in II than in I+ lambs. Mean inhibin concentrations were significantly lower in II lambs at 8 months, but did not differ significantly between genotypes at 2 or 5 month of age. The use of discriminant analysis techniques to segregate individual animals in group 1 on the basis of their plasma FSH and LH concentrations, correctly identified Inverdale genotype in 50/52 (96%) lambs at 2 months, 75/79 (95%) at 5 months and 118/122 (97%) at 8 months of age. Discriminant analysis was equally effective for segregating II ewe lambs (group 1) from fertile ewe lambs of I+ and ++ genotype (group 2, 97% correct at 5 months and 98% at 8 months). At no stage did inclusion of inhibin concentrations into the discriminant function alter the number of homozygous ewes misclassified. This demonstrates that infertile homozygous ewe lambs can accurately be distinguished from their fertile flockmates by using plasma concentrations of gonadotrophins alone, and that this can be achieved from as early as 2 months of age.

Age Factors↗
PubMed1985

Significance of particle size of mebendazole in the treatment of tapeworm infections.

Taenia hydatigena and Echinococcus granulosus in dogs have been used as a model to evaluate the response of these parasites to increasing doses of mebendazole in different dose forms (powder, micronized powder and tablets of micronized powder). Overall the micronized powder proved to be the most active, the tablets less so and the normal powder least active. Statistical confirmation was obtained that the use of this drug in different dose forms changed the rate of the response, suggesting that in the treatment of human hydatid disease caused by Echinococcus spp and cysticercosis caused by Taenia solium, the dosage form may be a vital factor in the drug's efficacy.

Animals↗
PubMed1983

Efficacy of praziquantel against ovine cysticercosis caused by Taenia hydatigena.

Praziquantel was evaluated for its larvicidal activity against naturally or experimentally induced Taenia hydatigena infections in sheep. The major criterion used for assessing efficacy was an estimate of the dose rate required to free 90 per cent of the sheep from infection (ED90) together with a 95 per cent confidence interval. With both light and heavy infections of three-month-old T hydatigena in lambs up to 12 months old, many larvae were killed. The ED90 and 95 per cent confidence limits for six-month-old and aged organisms was estimated to be 13.1 (5.5 to 31.4) mg/kg and 6.1 (2.4 to 15.5) mg/kg, respectively. Equivalent data for the ED50 were 3.4 (1.4 to 8.3) mg/kg and 1.3 (0.3 to 5.4) mg/kg, respectively. It was established that one of the factors involved in the efficacy of praziquantel was associated with the age of the larvae at the time of treatment, the drug being markedly more effective against older than younger organisms.

Age Factors↗
PubMed1981

Cestodes.

A review has been made of the advances in knowledge on the treatment of tapeworm infections of man and animals from the time of the introduction to dichlorophen in 1956. This opened up the era of out-patient treatment for human tapeworm infections. The drugs studied have been compared, where possible, on the basis of estimates of the single dose ED90 or the number of treatments required to reach that efficacy at safe dose levels. During the period under review, niclosamide, introduced in 1960 has been regarded as the drug of choice for the treatment of human tapeworm infections with paromomycin as a possible alternative. The bunamidine salts, introduced in 1966 permitted the treatment of Echinococcus spp in dogs. Several treatments were required to achieve acceptable efficacy. In 1975 praziquantel was introduced and based on the ED90, a single dose at no more than 10mg/kg removed all tapeworms responsible for the cestode zoonoses and for which data are available with the exception of H. nana and D. latum; these require a higher dose rate. In the mid 1970s, several benzimidazoles and praziquantel were shown to have activity against metacestodes. This has opened up a new field of research promising a practical outcome. No progress has been made during the period under review in finding effective ovicides.

Animals↗
PubMed1981

Factors regulating tapeworm populations: estimations of the duration of acquired immunity by sheep to Taenia hydatigena.

Lambs reared from birth in a 'tapeworm-free' unit were immunised at three months old by a parenteral injection of the embryos of Taenia hydatigena. Subsequently, they were grazed with unimmunised control animals on an egg-free pasture. At one, three, six, nine, 12 or 15 months after immunisation, groups of the treated and control animals were grazed for eight weeks on an experimental egg-contaminated pasture. Strong immunity was shown up to three months after immunisation by the presence of only a few pinhead lesions in the lamb's liver. At six and nine months after immunisation, the lesions were similar in size to those in the control animals. While a few organisms reached the abdominal cavity in animals grazed six and nine months after immunisation, no viable cysts were found until 12 months. Seven-year-old sheep, which had been naturally infected with T hydatigena at an early age but had rarely ingested eggs since, were also grazed on the egg-contaminated pasture. Populations of original and superimposed metacestodes were observed in the abdominal cavity of some of them. The first experiment investigated the duration of immunity to the embryo, reorganising larva and metacestode in the absence of further egg infections. The second experiment confirmed that original and superimposed cyst populations can coexist.

Animals↗
PubMed1980

Liver copper concentrations in red deer (Cervus elaphus) and wapiti (C canadensis) in New Zealand.

Concentrations of copper in livers from red deer (Cervus elaphus) or wapiti (C canadensis) were measured and classified according to the age and species of the animals whether farmed or feral, the area from which they came and their sex. Significant variations occurred with age, species, environment (farmed or feral) and area. Mean liver copper concentrations (after logarithmic transformation) ranged from 356 mg/kg of fresh matter in fetus/neonate to 10.5 mg/kg in mature animals.

Animals↗
PubMed1979

The effect of nitroscanate tablets of Echinococcus granulosus and Taenia hydatigena infections in dogs.

Tablets of micronised nitroscanate (nominal particle size 2--3 microns) were given to a total of 190 dogs that had been experimentally infected with either Echinococcus granulosus or Taenia hydatigena. The efficiency of the drug in tablet form in freeing dogs from tapeworms, was investigated. The dose rate at which 50 per cent of normally fed dogs can be expected to be freed from E granulosus was found to be 89 mg/kg (95 per cent confidence limits 55 mg/kg to 140 mg/kg). The 90 per cent effective dose rate was not determined within the range 32 mg/kg to 250 mg/kg. The dose rate at which 90 per cent of normally fed dogs can be expected to be freed from T hydatigena was 37 mg/kg (95 per cent confidence limits 23 mg/kg to 60 mg/kg).

Animals↗
PubMed1978

Factors regulating tapeworm populations: dispersion patterns of Taenia hydatigena eggs on pasture.

Two grazing trials using 'sentinel' lambs were undertaken to measure changes in the availability of eggs within 30 metres of deposition by dogs infected with Taenia hydatigena. In the first trial the experimental pasture was divided into nine equal plots; in the second trial, each of the nine plots was divided into sub-plots. In each trial, infected dogs were placed on the pasture for 10 days. Lambs were then grazed for 10 days immediately, 36 days and 56 days after the dogs had been removed. Changes in the dispersion pattern of the eggs over time and space were assessed by examination of the lambs for cysts at autopsy. In both trials, eggs spread radially within the grazing zone within 10 days, but 36 days after the removal of the dogs, their availability to the lambs was markedly reduced. In the first trial at five weeks, the height of grass (between 3 cm and 15 cm) did not modify egg availability. In both trials, despite differences in rainfall affecting the growth of grass and associated factors similar egg losses occurred.

Animals↗
PubMed1978

The effect of an antibiotic of the streptothricin family against Echinococcus granulosus and Taenia hydatigena infections in dogs.

The effect of an antibiotic of the streptothricin class on Echinococcus granulosus and Taenia hydatigena infections has been investigated in a trial involving 160 dogs. The drug showed significant activity in freeing dogs from Thydatigena, but the evidence for similar activity against E granulosus was less well marked. Vomiting and diarrhoea were common sequelae of dosing. The preparation tested consisted of four chemical components and the cestocidal value of each was not determined.

Animals↗
PubMed1978

The effect of diuredosan on Echinococcus granulosus and Taenia hydatigena infections in dogs.

Diuredosan has been tested against Echinococcus granulosus and Taenia hydatigena infections in dogs. The drug showed significant activity against T hydatigena, but there was no significant dose response curve against E granulosus in this trial. Two treatments at 50 mg/kg or 100 mg/kg, however, reduced the number of dogs infected with hydatid worms. Worms were still present in some dogs after three treatments at 50 mg/kg. Vomiting and diarrhoea were relatively common sequelae at and above 50 mg/kg.

Animals↗