There is a growing number of nutraceutical products for promoting tractability and reducing anxiety in horses, despite a virtual absence of scientific assessment of these products. The objective of this study was to compare the effects of acepromazine (ACE) and a magnesium-based antianxiety formulation in horses participating in tasks typical of normal equine management. Six horses were randomly allocated to one of the three treatment groups in a 2 × 3 randomized block design. Each horse was fitted with a heart-rate (HR) monitor, and received a single dose of ACE (0.5 cc/horse), the nutritional formulation (NUT), or a placebo paste exactly 30 minutes before commencement of tasks. Tasks included loading onto an equine weighbridge, loading onto a two-horse trailer, unaccompanied transport in a two-horse trailer, jugular venous blood sampling, and 10 minutes in a stall with an unfamiliar object. Stress response with respect to peak and average HR, time to completion of tasks, and plasma cortisol were measured. This study demonstrated that tasks inherent to modern equine management are sufficient to induce a stress response, as demonstrated by increased peak and average HRs, and increased plasma cortisol. The average HR of the earliest task (30 minutes after ACE and NUT administration) was effectively blunted by administration of ACE or NUT 30 minutes before onset of stress. It is concluded that oral ACE and NUT reduce HRavg during a stressful task with which they were challenged 30 minutes after administration. Effects of these treatments on plasma cortisol require further research.