Simple Summary: The majority of the bits used for working horses in Senegal are made of construction iron, recovered from the rubble of destroyed houses or near construction sites. The poor design, shape, fit and quality lead to injuries in the horses' mouths which can impair their welfare by potentially causing discomfort, pain, distress and difficulty eating. To address this, Brooke—a charity aiming to improve the welfare of working horses, donkeys and mules—devised a pilot project to manufacture and trial improved bits for cart horses working in transportation of people and goods. This study has demonstrated the feasibility of producing an alternative bit design for cart horses that is low-cost and locally crafted from aluminium, which can improve upon bit-related aspects of cart horse welfare over a relatively short time period of 21 weeks. The improved bit designs have scope to positively impact upon large numbers of working horses in Senegal and beyond, whilst also representing a potential livelihood or income diversification opportunity for the local artisans who manufacture them and the vendors who sell them. Bits used for cart horses in Senegal are typically made of recovered construction iron and often have defects related to design, shape, fit and metal quality. Consequently, there is widespread presence of bit-related oral injury amongst these equids. It was hypothesised that improving bit design would ameliorate bit-related welfare issues for working cart horses. This study aimed to develop locally made alternative bit prototypes and test their efficacy as less harmful to working horses, and their acceptability to their drivers. Eight animal-based welfare indicators (four physical and four behavioural) were designed to measure positive or negative effects of the new bits. Following a testing phase to appraise and mitigate potential animal welfare risk associated with the alternative bit designs, a total of 540 driver/horse combinations were opportunistically selected across five municipalities in Senegal. Welfare indicators were observed when new bits were introduced and again after 21 weeks of daily use. The results indicated statistically significant improvements in all welfare indicators measured (i.e., lesions on lip commissures, tongue, buccal mucosa and bars; and open mouth, tongue loll, head toss/shake, and head tilt/turn behaviours). None of the drivers reported any difficulty with horse control, nor chose to revert back to their original bits. Whilst acknowledging the limitation of inability to control all potential confounding variables, these preliminary findings suggest the bit itself as an important contributor to oral injury, and the possibility to improve this through alternative bit design that is low-cost, locally produced and acceptable to drivers. [ABSTRACT FROM AUTHOR]