Impact of Mounted Loads on Welfare of Working Equids

In developing countries, there are approximately 112 million working equids (horses and donkeys) and most of them are subject to overloading. Overloading is associated with serious welfare problems. Developing a deeper understanding of safe loading capacity of equids is important for both effective performance and welfare. Carrying loads that are beyond the normal abilities of equids have negative effects on working equid, including causing gait asymmetry or lameness. It is important to determine how to carefully quantify the load carrying capacity of working equids. Traditionally, measurement of the amount of ‘bone’ was used, and more recently gait symmetry has been identified as a potential marker for loading capacity. There are many options to assess the effect of loading on an animal’s body, but these have been inconsistently applied making it difficult to reach a consensus. We summarise current knowledge of load carrying ability for horses and donkeys and the different parameters used to determine the effect of loading on these equids. Assessment of stride parameters and gait kinematics provides insights into adaptations to loading and may help determine loading limits. Physiological factors such as the ability to regain normal heart rates shortly after working is an important tool for equine fitness assessment. Oxidative stress, plasma lactate and serum creatine kinase activity are reliable biochemical indicators of loading ability. For monitoring stress, salivary cortisol is superior to serum cortisol level for assessment of hypothalamus-pituitary-adrenal axis and is related to eye temperatures, but this has yet to be interpreted in terms of load carrying ability in equids. An equine ethogram has been used to assess pain-associated behaviors in horses, which may be useful when used by trained assessors. More recently, a grimace scale for pain has been developed for use in donkeys, although this has not yet been used in the field. There are also concerns about the validity of ethograms for use in working donkeys due to the stoicism of these animals. The use of the equine ethogram has demonstrated an induce behaviors associated with musculoskeletal pain and temporary lameness in horses. Further research is needed to develop evidence-based guidelines for maximum loading in equids. Quantified loading limits or indicators of overloading could be used by stakeholders working with equids to limit overloading and to improve the welfare of these animals.