Bone development on the distal phalanx of New Zealand dairy cows : the link to lameness : a thesis presented in partial fulfilment of the requirements for the degree of Master of Animal Science, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand

Abstract

Claw horn disruptions are important cause of lameness and affects cattle around world, causing major economic and welfare problems for dairy industry. Inflammation from an active CHD can lead to bone growth (exostoses) on the distal phalanx, which predisposes the animal to further CHD in future and damages the internal anatomy of the hoof. Previous quantitative studies have evaluated, using µ-CT, bone development on the distal phalanx of cows which are housed for most or all of the year, and identified that bone growth is associated with age, lifetime history of CHD and chronic lameness. The aim of the present study was to evaluate whether digital photography could be used instead of µ-CT to obtain linear measurements of exostoses and to find whether bone development was associated with age, claw type and lameness history in the lactation prior to culling in pasture-based cattle. Distal phalanxes (160) were collected from the hind feet of 40 dairy cows after slaughter. Digital photographs were then taken, and bone growth measurements were made at 4 locations near the flexor tuberosity (A to D) guided by the method using µ-CT. Modelling was then used to identify whether age, claw type and lameness history were associated with the average of the sum of measurements A to D across all four claws of an individual cow (Ave BG) and the highest sum of A to D for an individual claw within a cow (BG Max). Only minor modifications were necessary to the measurement method to account for the differences between µ-CT and digital photography, thus digital photography provides an economic alternative to the use of µ-CT to study bone development in the distal phalanx. An association was found between age and BG Max and Ave BG with a one-year increase in age being associated with BG Max increasing by 1.12 (95% CI: 1.03-1.21) times and Ave BG increasing by 1.09 times (95% CI: 1.04-1.14). Outcomes for history of lameness were also compatible with lameness increasing bone growth, with the point estimate for BG Max being 1.61 (95 CI: 0.88-2.95) (equivalent to 5 years of age effect) and for Ave BG being 1.25 (CI:0.89-1.78) (equivalent to 3 years of age effect). However, the data were also compatible with no biologically important association between lameness and bone growth. The majority of the differences between claws in BG Max and Ave BG were driven by differences in measurement D as 136/160 claws had zero values for measurements A, B and C but all claws had values > 0 mm for D. In all claws where the only measurement >0 was measurement D, the bone development appeared to be normal being smooth in appearance without any pointed edges or rough surfaces. Analysis of the effect of age on measurement D (in claws with A, B, C= 0), and on the sum of A, B and C was consistent with the hypothesis that the principal effect of age was through its impact on measurement D, as the effect of age on measurement was similar to its impact on BG max, and the analysis of age on sum of A, B and C was compatible with no effect. However, these are preliminary data, and this hypothesis needs more investigation.