Characteristics of laminitis and associated claw lesions in dairy cows in Nairobi and its environs
Lameness in dairy cows causes vast economic losses by reducing production and reproductive efficiency. Claw horn lesions are the most common cause of lameness, but the extent to which they contribute to dairy cow lameness in Kenya is undetermined. Furthermore pathomorphological changes associated with laminitis in cattle, and which would help in understanding of its pathogenesis are not yet well studied. The objectives of this study were therefore to: 1. Determine the prevalence of subclinical and chronic laminitis and related claw lesions in dairy cows in Nairobi and its environs, 2. Evaluate association between laminitis and related claw lesions with cow-and farm-level risk factors, 3. Determine radiographic and pathomorphological characteristics of claw lesions in claws collected from abattoirs. The study was carried out in three phases. In phase 1, retrospective data on cases of dairy cows admitted for treatment of claw lesions in the Large Animal Hospital of the Faculty of Veterinary Medicine, University of Nairobi, Kenya in the period 1981 to 2006 were collected. The data collected included type of foot lesion, the foot affected and the clinical outcome in each case. Phase 2 was a prospective study in which 29 zero-grazed smallholder farms each with 5- 20 cows, and 3 large-scale pasture-managed farms each with more than 60 cows, were purposively selected. Farm-and cow-level data were collected using coded questionnaire forms through direct-respondence from the farmers, farm managers or stockmen and were related to parity, lactation, housing and nutrition. In each farm, cows were selected xxxii by simple systematic sampling and included both the lame and non-lame cows. A total of 300 cows were selected. Their gait was evaluated by a conventional locomotion scoring system. The hind claws of each cow were thoroughly washed and examined for laminitic claw lesions. A 1-2 mm thickness of the horn was trimmed from the sole to expose any underlying lesion, and the findings recorded in data collection forms. Locations of lesions on the weight-bearing surface of the claw were categorized according to 6 conventional zones of the sole, while sole haemorrhages were categorized according to 5 conventional haemorrhage scores. Toe angle as well as length and width of the claw were measured. During phase three, 159 cow feet (318 claws) samples from two purposively selected abattoirs in Kiserian and Wangige Market were collected. The claw samples were radiographed in dorso-palmar or dorso-plantar projections for examination of pedal bone changes. Examination of the claws for gross lesions was done as in phase 2. Further to this, sagittal section of each claw was made, after which the corium and the pedal bone were examined. Corium specimens were taken from 10 claws with subclinical laminitis and 10 claws with chronic laminitis for histological examination. Further corium specimens were taken from 5 claws with subclinical laminitis and 5 claws with chronic laminitis for examination under transmission electron microscope. Controls for histological and electron microscopic examination were corium specimens from claws that did not show any form of laminitis. The specimens were processed following standard histological and electron microscopic procedures. Findings of radiographic, histological and electron microscopic examination were recorded. xxxiii Analysis of all the data collected was done using descriptive statistics, tests of association, and stepwise logistic regression. The stepwise logistic regression was done by forward selection and backward elimination of predictor variables (risk factors) while putting into consideration the effects of confounding and interaction between them using SAS © 2002-2003. The results of retrospective study showed that interdigital necrobacillosis (foot rot) had the highest (35.7%) prevalence followed by interdigital fibroma (11.9%) and sole abscess (11.1%), but prevalence of laminitis (0.79%) was very low. Results of the prospective study indicated that most (88%) of the cows had claw lesions, of which a high (69%) percentage of them had no signs of lameness. Prevalence of subclinical laminitis was 49.3% and 34.6% for prospective and abattoir studies respectively, while that of chronic laminitis was 21% for both prospective and abattoir studies. Among other claw lesions, sole bruising had the highest prevalence of 45% (prospective) and 78% (abattoir), followed by heel erosion at 27.3% (prospective) and 41.5% (abattoir). Claw deformities had prevalence of approximately 45% for both prospective and abattoir studies. Sole haemorrhages were present in 82% of the cows that had laminitis, of which 34.7% involved zone 4 of the sole. Severity (scores 2 and 3) of sole haemorrhages was seen in chronic laminitis, and it significantly (p < 0.0 5) involved zones 2, 3 and 6 compared to zones 1, 4 and 5 of the sole. Regular (≥ 2 times/day) concentrate feeding significantly (χ2 = 3.84, r = 0.1, O.R = 1.9, p< 0.05) enhanced occurrence of subclinical laminitis. Fewer cubicles than the number of xxxiv cows (overcrowding) (χ2 = 12.09, r = 0.4, O.R = 1.6, p < 0.05), and having more than three parities (χ2 = 5.36, O.R = 1.5, p < 0.05) were the risk factors that significantly enhanced occurrence of chronic laminitis. Slight to moderate (scores 1 and 2) sole haemorrhages (χ2 =18.01, r = 0.6, O.R = 39.3) mainly involving zone 4 of the sole (χ2 = 22.03, r = 0.3, O.R = 3.3) were strongly and positively associated (p < 0.05) with presence of subclinical laminitis. Claw overgrowth (χ2 = 91.83, r = 0.6, O.R = 14.1), horizontal ridges (χ2 = 31.20, r = 0.5, O.R = 12.4), and concave claws (χ2 = 11.98, r = 0.4) were strongly and positively associated (p < 0.05) with presence of chronic laminitis. High locomotion scores were invariably associated (χ2 = 36.76, r = 0.6, O.R = 4.3, p < 0.05) with chronic laminitis compared to other related claw lesions. The main radiographic changes seen on the pedal bone were: dilated vascular channels (60.8%), prominent (but not dilated) vascular channels (24.1%), irregular margins (13.9%), exostosis (8.2%) and narrowing of the bone (5.7%). Outgrowths on the pedal bone had low (< 5%) prevalence but were a new finding. Key histopathological changes observed in the corium of laminitic claws were: arteriovenous shunts, vascular wall disruptions, vascular thrombosis, dermal-epidermal junction disruptions, epidermal hyperplasia, , oedema in the dermis, spongiosis and degeneration in the connective tissue. Electron microscopy revealed presence of fibroblast degeneration, vacuolization within the cytoplasm of fibroblasts, vascular endothelial cell damage, degeneration and necrosis as well as disoriented smooth muscle cells of the blood vessels. xxxv From this study, it was concluded that: 1. The prevalence of laminitis (70.3%), mainly subclinical, in zero-grazed farms in Nairobi and its environs is high, 2. Haemorrhaging in the sole can be a main diagnostic sign of subclinical laminitis, and which when present together with claw deformities, distinguishes regular from laminitic deformities, 3. Concentrate feeding enhances occurrence of subclinical laminitis, while more than 3 parities and overcrowding enhance chronic laminitis, 4. Narrowing and outgrowths of the pedal bone, connective tissue degenerative disruption, epidermal cell spongiosis, epidermal hyperplasia, fibroblast degeneration and vacuolization of the cytoplasm, which have not been recorded previously, were observed as new findings in laminitic claws. Further research needs to be carried out in different representative parts of Kenya to establish whether the laminitis situation is widespread and similar in findings to the current study. In addition, progressive systematic research using longitudinal or casecontrol studies needs to be done to establish the actual pathogenesis of laminitis.