Lesions and microscopic structure of claw horn in dairy cattle

Foot health in cattle is highly dependent on the integrity of claw horn. This study was carried out to investigate relationships between the microscopic structure of claw horn and the development of claw lesions in dairy heifers. The hypothesis was that the degree of microscopic abnormalities in horn structure would be related to the severity and extent of gross lesions. A study of gross claw lesions was made by examining the feet of 31 firstcalving Holstein-Friesian heifers on eight occasions during the period from four weeks before calving to 32 weeks after calving. The objective was to obtain a detailed record of the development of lesions, with regard to location, size and severity. A method involving image analysis of photographs was devised and used to measure the size of haemorrhages and other lesions of the sole and white line. The severity of lesions was assessed by subjective methods. Locomotion scoring was used to quantify lameness. Factorsa ssociatedw ith calving and housing contributed to an increasei n the number, extent and cumulative severity of claw haemorrhages. The post-calving increase in lesions, and the subsequent recovery, occurred later in the sole than in the white line. The greatest number, extent and cumulative severity of sole lesions were recorded at 14 weeks post-calving. The equivalent scores for the white line were highest at four or nine weeks post-calving. The incidence of lameness in the study cohort (26%) was average for British dairy herds but the mean prevalence (1%) was low. Qualitative and quantitative investigations of horn structure were made at both the electron microscopic and light microscopic levels, using samples of horn from animals of the study cohort. Stereological methods were applied to transmission electron micrographs to estimate the volume fraction of intercellular material in horn from the white line. This study did not show any relationship between the volume fraction of intercellular material and the severity of gross claw lesions. However, it was observed that areas of increased intercellular material, abnormal intracellular structure and cellular disintegration were very localised. Horn exhibiting disturbed keratinization and degeneration consistently occurred in broadened regions of the interdigitating horn (terminal horn) of the white line. Such horn was characterised by a high affinity for histological stains and, in some cases, contained blood breakdown products. There was some evidence to suggest that a higher proportion of abnormally keratinized horn (as identified by histological staining) is present before calving in the white line of cattle which subsequently suffer more severe and extensive claw lesions. This study provided data on the development of claw lesions in a dairy herd without a specific lameness problem, giving a baseline with which other herds can be compared. A difference in the pattern of development between sole and white line lesions was revealed. This suggests that, contrary to common assumption, the timing and possibly the pathogenesis of lesions differs between these two regions of the foot. Microscopic studies demonstrated that increased amounts of intercellular material in horn occur in conjunction with abnormal intracellular structure. Such regions of ultrastructural abnormality can be detected by histological staining. This offers a potential technique for further investigations of the relationship between horn structure and claw lesions.