Sheep health: research developments and emerging problems

Abstract

AbstractRelative to other livestock sectors sheep production has a high wastage through mortality, suboptimal husbandry practices and premature culling. A significant but unquantified component of this loss is attributable to infectious and parasitic disease. Some common infectious diseases (e.g. those caused byClostridia) are amenable to effective control but regular sporadic outbreaks indicate that, from time to time, control measures fail or are improperly applied. Other diseases, notably those causing abortion, continue to present problems, particularly chlamydial abortion and toxoplasmosis. Inability to diagnose infection before the onset of clinical signs hinders the control of scrapie and pulmonary adenomatosis (jaagsiekte) and the only vaccine against orf is of limited efficacy.However, the new information being generated by application of molecular biological techniques in some of these problem areas carries promise of improved control. Good examples are provided by research which has led to a blood test for discriminating between sheep that are genetically susceptible or resistant to scrapie and by studies onChlamydia psittaciwhich have identified essential protective antigens and which thereby improve prospects for significant vaccine enhancement.The world-wide importance of gastrointestinal parasitism and the emergence of anthelmintic resistance have spurred efforts, internationally, to develop an alternative biological control system. Evidence that protective vaccination may be feasible is accruing but the time scale to a real product may be long.Factors to be considered in assessing future disease trends include the impact of a ‘frontier-free’ Europe, changes in husbandry practices, introduction of new livestock species, altered land use and climatic change resulting from global warming. Some predictions are made.