Derbyshire, Marjorie B.

2018-01-31T11:42:28Z

2018-01-31T11:42:28Z

1975

Qualitative and quantitative techniques have been used to compare the follicle populations of control and Border disease affected foetuses and lambs of the medium - fine fleeced Cheviot x Dorset Horn cross, and the coarse fleeced Scottish Blackface breeds.

In the Cheviot cross, the main effect of the disease is to cguse primary follicle hypertrophy, which is first apparent at 115 days' gestation and is accompanied by an increased fibre size and an increased frequency of medullation. These changes are not known to occur in any other infectious ovine disease. The normal suppression of follicle activity which occurs perinatally and at about the time of birthcoat shedding, and also during the :;inter months is present in Border disease affected animals. Thus, the differences observed between. the follicle populations of control and affected animals. at these times are less obvious. A reduction in the number of secondary follicles which develop is also apparent in Border disease, but this may be an indirect effect of the disease process caused by increased primary. follicle size or possibly by impaired foetal nutrition resulting from the placentitis which.is also a feature of the disease.

The developing primary follicles are susceptible to the effects of Border disease following maternal inoculation at up to 80 days' gestation. The reason for the loss of susceptibility thereafter is not clear, although it may be related to the development of a foetal immunological response to the agent.

Studies of the literature on epidermal- dermal interaction and studies of the disease process in the Cheviot qross suggest that the follicle papilla determines the morphology of the follicle and fibre. Thus modification of the cells of the papillae of primary follicles by the disease process probably causes follicle hypertrophy. Post -natal studies.indicate that this effect is durable if not permanent, and thus a new concept is introduced, namely that of a developmental anomaly leading to ordered hyperplasia rather than the more usual disordered hypoplasia.

The development of the follicle population of the control Scottish Blackface resembled that of the Border disease affected medium - fine fleeced Cheviot cross. Border disease in the Blackface did not cause further primary follicle hypertrophy. As a working hypothesis to explain these findings, it is proposed that Border disease prevents the function of an inhibitor substance which normally controls primary follicle growth in medium and fine fleeced breeds. Interference with the functioning of the inhibitor contributes to the development of a coarse fleece.

An analogy exists between the effects of Border disease and the effects of the mutant N and nr genes in the N -type Romney, which also cause primary follicle hypertrophy, and the analogy underlines the hypothesis that Border disease mimics a genetic effect in the skin.

Baselines can be established to determine abnormal medullation in fine and medium fleeced breeds, and it is suggested that the frequency of medullae or large medullae in central primary follicles should be used depending on the breed studied. Peri -natal sampling and sampling during the birthcoat shedding phase, during the winter months and during terminal illness should be avoided if useful results are to be obtained. With these provisos, histological examination of the skin could be a useful tool in medium and fine fleeced breeds to detect adult carriers and affected lambs.

http://hdl.handle.net/1842/27897

The University of Edinburgh

Annexe Thesis Digitisation Project 2017 Block 16

Already catalogued

Studies of the skin follicle development in Border disease of sheep

Thesis or Dissertation

PhD Doctor of Philosophy