Welfare of working mules

Although mules (E. asinus x E. caballus) are essential for pack work and increase in resilience in mountainous areas, little research has been done on this species. Working mules, as other working equids, are confronted with different risks for their welfare, these include inadequate human-animal interactions, inappropriate working practices, problems in the correct design of harnessing systems and a lack of understanding of their behavior and biology which may lead to negative perceptions about this hybrid. During the last years we have tried to understand better some of these risk factor in order to develop welfare strategies.

Many people consider mules as more aggressive than horses and donkeys, reason why we studied the perceptions, attitudes, empathy and pain perception of soldiers about mules used by the Chilean Army. By using different instruments to assess these constructs we found that there was a wide range of ages and years of experience working with equids among soldiers, which may affect their perceptions. Significant positive correlations were found between human empathy, animal empathy and pain perception. Soldiers show a preference for working with mules over donkeys and horses, since they describe them as more intelligent and stronger, in particular when logistic work in mountain areas is required. Nevertheless, they were described as more aggressive than horses and donkeys. Donkeys were the least preferred species to work with by soldiers. Text mining analysis showed three clusters associated with the mules’ needs according to soldiers’ knowledge, these clusters represented nutritional, environmental and health needs. In the same line, relevant relations were found for the word “attention” with “load”, “food”, and “harness”. When asked what mules signify for them, two clusters were found, associated with mules’ working capacity and their role in the army. Relevant relations were found between the terms “mountain”, “support”, and “logistics”, and also between “intelligent” and “noble”.

Another intrinsic risk factor for working mules’ welfare could be the selection of morphological attributes that are less suitable for work. Physical attributes are important features that can affect management, performance, and welfare. We have assessed 16 morphometric traits and six morphofunctional indexes of army mules in order to understand their aptitude for work but also to understand which type of mules soldiers prefer to work with. The studied mules were well-balanced, with more riding and saddle type aptitude than for load work. According to responses, the ideal pack mule should be docile, medium size, resistant and suitable for load work in mountainous terrain. Medium size mules, with a height to the withers of 140cm were preferred, probably because they are easier to handle and pack than large mules of around 160cm to the withers, making the work of soldiers easier.

Size and morphology could also influence load and work capacity, this is why we investigated the performance and recovery capacity of three different sizes of mules (small, medium and large) while carrying different loads (80, 105 and 130 kg) after a 2km and an 8km walk. Physiological indicators associated to heart rate, respiratory rate and rectal temperature were assessed. Only for the 130kg load, after a 2km walk, mules were not able to recover basal frequencies after 10 minutes (P< 0.05). In terms of blood indicators, only serum cortisol showed significant changes for all loads (P< 0.05), recovering basal concentrations after 2 hours finished the 2km walk. For the 8km walk only the 105kg load was assessed, the heart rate and respiratory rates showed significant increases, recovering basal frequency after 10 minutes past the end of the walk. In terms of blood indicators, only potassium, fibrinogen, and cortisol showed significant differences between sampling times (P< 0.05). Potassium decreased after 2h past work, fibrinogen showed an increase 5 days after work, and cortisol showed a significant increase at arrival, but then returned to basal concentrations 2 hours later. We did not find an effect of mule size on their physiological response to work. Another welfare concern when mules perform pack work is that the can develop skin wounds and lesions on harness related areas of the body, but also muscular and bone damage that are not always visible during clinical examination. In particular, this can happen with a harnessing system that does not fit appropriately. We have used thermographic imaging and pressure sensors as non-invasive diagnostic alternatives to understand the effect of different loads on the back of mules. A crossover design was used with twelve mules carrying three different loads (80, 105, and 130 kg) for two kilometers. Four pressure sensors were placed in the harnessing system to assess the pressure (N) of the loads. Thermographic images of the back were taken daily before and up to five days after the harnessing work. We found that heavier loads (105 and 130 kg) generated a significant increase of temperature (P< 0.05) in all the analysed areas of the mules’ back, with no significant differences between anatomical areas. The pressure sensors did not reveal significant differences between load treatments or between anatomical areas, also there was no evidence of a correlation between pressure and temperature.

There are still grey areas that need to be investigated, in particular in terms of mules’ behavior and biology. Also we need to consider that the variability of mules features between countries is huge, since many characteristics will depend on the selection of the jack and mares breed, so it is difficult to generalize findings from one groups of mules under a particular geographic and cultural system to another.