Studies on the development and innervation of the bovine and caprine horn
The main objective of this study, as detailed in Chapter 2, was to investigate the nerves innervating the horn base in cattle and goats, paying particular attention to the contribution of the N. sinuum frontalium. The study involved the gross dissection of twenty-five cattle, aged between 2 days and 4 years, as well as twenty-four goats aged between 10 hours and 6 years. In addition to the dissections, the neurotracer Fluorogold was applied to the cut horn bases of two calves and two 15-month-old heifers. Fluorogold was taken up by cut nerves and was then transported in a retrograde manner along the nerves. The inspection of nerve sections under the fluorescence microscope revealed Fluorogold granules in the R. zygomaticotemporalis of all four animals, as well as in the N. infratrochlearis of two animals and in the N. frontalis of a single animal. Fluorogold granules were not present in either the N. sinuum frontalium or the Nn. cervicales. However, osmium-stained histological sections of the horn base revealed the presence of nerve fascicles, presumed to be branches of the N. sinuum frontalium, in the cornual diverticular lining of cattle over 2 years of age and goats over 4 years of age. These results demonstrated that in cattle the R. zygomaticotemporalis is not the only nerve supplying the horn base. Furthermore, in mature cattle and goats the N. sinuum frontalium needs to be blocked before the animal is dehorned. The objective of Chapter 3 was to investigate the sensory receptors present in the horn bud of calves and kids. For this study immunohistochemistry was used in conjunction with transmission electron microscopy. Immunohistochemistry utilized neurofilament and S-100 antibodies which demonstrated nerve fibres and Schwann cell cytoplasm respectively. In this study numerous free nerve endings, known to be nociceptors, were identified in both calves and kids. In addition, bulbous corpuscles, Merkel cells and intraepidermal nerves were demonstrated.