Lameness in herds during one year was commonest in the first month of lactation (15 per cent of all cases). Leg lesions were particularly common at this time (24 per cent of all cases of leg lesions) but white line abscess and sole ulcer were more common a month later. Foul-in-the-foot was one of the two most common lesions at all stages of pregnancy and lactation, and white line abscess the most common (20 per cent of all lesions) in late lactation. Both sole ulcer and underrun heel had lower incidence in the second half of the year than the first. White line abscess was particularly common in March and November although there were significant interactions between month and veterinary practice; foul-in-the-foot was most common in October. Susceptibility to lameness increased with age; 10-year-old cows were over four times more likely to develop lameness than three-year-old cows. This was due particularly to increased incidence with age of white line abscess and sole ulcer and, to a lesser extent, underrun heel. In contrast, foul-in-the-foot and leg lesions showed little change with age. Whereas these lesions accounted for 68 per cent of the total in cows up to two years old, they accounted for only 15 per cent of all lesions in cows over 10 years old. White line abscess was slightly commoner in cows with large heart girths.

The incidence of lameness in herds visited by veterinary practitioners in winter (0.87 cases per 100 cows per month) was greater than in summer (0.71 cases per 100 cows per month). The relative proportions of leg lesions and underrun heel were higher, and those of foul-in-the-foot, interdigital hyperplasia and foreign body in the sole were lower in winter than in summer. In winter, leg lesions and aseptic laminitis were most common in cows housed in cowsheds, white line abscess in cows in strawyards and sole ulcer in cows in either cowsheds or cubicles with concrete yards. The overall incidence of lesions was lower in strawyard accommodation (0.71 cases per 100 cows per month) than in cubicles with yards (0.93 cases per 100 cows per month). Veterinary practitioners saw proportionally fewer cases of foul-in-the-foot but proportionally more cases of sole ulcer in larger than in smaller herds. The animal incidence of lameness ranged from 1.7 to 11.4 per cent among practices; in 20 practices which recorded a total of at least 100 lesions in both summer and winter there was a large variation in the proportions observed of each lesion. A principal component analysis contrasted those practices which tended to see mainly cases of white line abscess, white line separation, foul-in-the-foot and leg lesions with those which saw mainly cases of underrun heel, interdigital hyperplasia, punctured sole with pus and sole ulcer. Twenty-nine per cent of cases of underrun heel and 22 per cent of cases of both deep sepsis and interdigital hyperplasia occurred in conjunction with another lesion.

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The incidence of lameness in cows recorded by five veterinary practices over one year and one practice over four years was plotted with rainfall and potential soil moisture deficit. Correlation coefficients calculated between lameness, rainfall and potential soil moisture deficit over two-week periods showed the incidence of lameness in summer to be significantly related to the potential soil moisture deficit in the same two-week period and rainfall in the previous two-week period. Differences in patterns of lameness incidence among practices and years were also partly explained by differences in rainfall and potential soil moisture deficit; however, these effects were small compared with those of other factors that affect lameness incidence such as herd size, age and stage of lactation.

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