Longitudinal and cross-sectional studies to evaluate the risk of sarcoid associated with castration

In order to investigate whether gender and castration have an effect on the time to the development of sarcoids, a retrospective study in a population of donkeys was conducted using survival analysis techniques. Univariable Kaplan Meier product limit curves identified males as having significantly lower survival probability, or higher risk of developing sarcoids, than females (P < 0.01). Cox's proportional hazard model was used to assess the effect of age at entry to the population whilst simultaneously considering the effect of gender on the hazard of developing sarcoids. Age at entry and gender were both significantly associated with the hazard of sarcoid (P < 0.01). Animals younger at entry were at increased risk of being diagnosed with sarcoids and the hazard ratio for being male was 1.9. Although male animals castrated after entering the population had significantly poorer survival rates than those castrated prior to entry, this effect was not significant when age at entry to the population was fitted to the model, demonstrating that the castration procedure within the population per se was not a risk factor. Although there was a trend toward stallions being at increased risk when compared to geldings, the effect was not statistically significant, particularly when controlling for age. It was concluded that a multicentre study or meta-analysis will be necessary to resolve the issue of risk associated with castration.