Assessing the impact of draught load pulling on welfare in equids

Abstract

About 112 million working equids are the source of income for 600 million people globally. Many equids are used for pulling loads (up to 15,000 kg per day) to transport goods. Most of them are associated with brick kilns, mining, and agriculture industries in developing countries. They may suffer from welfare issues such as overloading, being beaten, and being forced to work for long periods. These issues may occur due to a poor understanding of load-pulling equids. Understanding their capabilities and the elements that influence them is critical for efficient performance and welfare. The measurement of stride characteristics and gait kinematics can reveal loading adaptations and help identify loading limitations. It is known that both loading and fatigue change the locomotor patterns of load-pulling horses. Heart rate is a stress quantifying metric and an important representative of the speed of work and draught force. Heart rate variability is a regularly used statistic to quantify a physiological response to stresses, but it has never been used for load-pulling equids. Changes in blood lactate, nitrogen, oxygen, and carbon dioxide contents are reliable biochemical indicators of the effects of load pulling. Changes in plasma cortisol levels reflect the intensity of exercise and stress levels in horses while pulling a load. However, eye blink rate is a cheap, simple, and immediate indicator of acute equine stress, and we suggest it may be used to aid in load-pulling equine welfare assessment. However, further research is needed for a standardized and evidence-based draught load pulling capacity of working horses, mules, and donkeys.

Keywords: cart pulling; donkey welfare; equine behavior; equine physiology; equine welfare; horse welfare; limb biomechanics; mule welfare.

Figure 1

Draught load pulling mule in a brick kiln production system (left) and fodder cart pulling donkey in a rural area (right) in Pakistan. Photo: Syed S. U. H. Bukhari.

Figure 2

Common welfare problem of equids associated with draught load work.

Figure 3

Horse pulling a load (W) with a zero-draught angle as the shafts are parallel to the ground. The arrow indicates the direction of the load’s force (F). The horse only needs to exert a horizontal force to move the load.

Figure 4

Horse pulling a load (W) with a draught angle (x) as shafts is not parallel to the ground. The arrow indicates the direction of the load’s force (F). The horse needs to exert both horizontal and vertical force to move the load, as the load is pulling back and down on the horse.

Figure 5

Physiological parameters studied in relation to load pulling in equids. Sign (+) indicates, value of the respective parameter increases in response to work. Symbol (*) indicates, parameter value increases in untrained equids but remains normal in trained working animals. Sign (T) indicates that as work intensity increases, muscle fibers are recruited in the order from type I to IIA, and IIB.

Figure 6

Behavioral responses of load pulling donkeys in response to different load weights (47).