Domestic horse management contrasts with their natural environment and behavioral needs. Small stalls and regulated feedings increase standing and reduce foraging which could impact the welfare of the horses. Enrichment seeks to encourage mental stimulation and species-typical activity budgets; however, more research is needed to understand how type of enrichment and provision time influences horse behavior. Furthermore, physiological parameters can provide insight of health and mental state, but enrichment effects on the physiology of horses are under-researched. This study analyzed physiology and behavior of nine stalled quarter horses throughout the day when provided a hay feeder (HF), activity ball (AB), and mirror (MIR) to better understand their effects on welfare. Horses were randomly divided into three groups and monitored over three trials, with each consisting of a control day and enrichment day. Each group received a different enrichment item per trial. Observations were conducted for 30 minutes four times per day (morning, noon, afternoon, and evening). Enrichment was removed between observations and during 5-day wash out periods between trials. Heart and respiration rate were recorded during observations approximately every 21 seconds through Nightwatch® Smart Halters™; behaviors were later scored via video recordings in BORIS using focal instantaneous scan sampling at 30-second intervals. Effects of type of enrichment, time-of-day, and possible interactions on each variable were tested using generalized linear mixed models; Tukey’s HSD multiple comparison procedure were used for post-hoc comparisons (statistical significance set at p≤0.05). No significant differences in respiration rate were recorded, but enrichment significantly increased heart rate from control at all times (Morning: HF p=0.027, AB p=0.027, MIR p=0.022; Noon: HF p=0.022, AB p=0.028, MIR p=0.019; Afternoon: HF p=0.036, AB p=0.027, MIR p=0.024; Evening: HF p=0.038, AB p=0.031, MIR p=0.036). This indicates high arousal in response to enrichment, and heart rate increased the most when horses were provided HF versus other enrichment items. Provision time did not affect heart rate within any of the treatments except MIR in which horses showed lower heart rate in the evening (Morning p=0.026; Noon p=0.031; Afternoon p=0.029). Between the three enrichment treatments, horses showed no significance difference in enrichment interaction and all items appeared equally engaging. Compared to control, all enrichments increased foraging (Morning: HF p=0.035, AB p=0.038, MIR p=0.041; Noon: HF p=0.029, AB p=0.036, MIR p=0.032; Afternoon: HF p=0.025, AB p=0.023, MIR p=0.039); decreased standing rest (Morning: HF p=0.036, AB p=0.035, MIR p=0.042; Noon: HF p=0.036, AB p=0.032, MIR p=0.041; Afternoon: HF p=0.023, AB p=0.026, MIR p=0.023); decreased standing alert (Noon: HF p=0.036, AB p=0.032, MIR p=0.037; Afternoon: HF p=0.029, AB p=0.028, MIR p=0.022); decreased social interactions (Noon: HF p=0.032, AB p=0.025, MIR p=0.039; Afternoon: HF p=0.021, AB p=0.029, MIR p=0.023); decreased frustration behaviors (Noon: HF p=0.035, AB p=0.041, MIR p=0.027; Afternoon: HF p=0.031, AB p=0.041, MIR p=0.043); and increased other behaviors (i.e., drinking, grooming; Afternoon: HF p=0.034, AB p=0.032, MIR p=0.029). However, while all items appeared effective enrichments overall, some variation in treatment effects were present. MIR resulted in no significant differences in locomotion compared to control; however, HF and AB increased locomotion (Morning: HF p=0.031, AB p=0.019; Noon: HF p=0.042, AB p=0.031; Afternoon: HF p=0.025, AB p=0.036). Horses showed increased foraging when provided HF at noon compared to AB and MIR (p=0.036 and 0.029, respectively) and had decreased standing alert in the afternoon compared to AB (p=0.036). HF and AB increased locomotion compared to MIR (Morning: HF p=0.039, AB p=0.043; Noon: HF p=0.026, AB p=0.023; Afternoon: HF p=0.032, AB p=0.037). Overall, the activity budget of horses when provided the HF suggests this item may more effectively fulfill overall behavioral needs; however, these results suggest that enrichment items could be selected to target specific behavioral needs and may be best implemented at certain times. Specifically, behavioral effects often appeared to be stronger during midday as seen within HF and AB treatments in which horses had increased locomotion at noon (HF: Morning p=0.039, Evening p=0.035; AB: Morning p=0.38, Evening p=0.026) and afternoon (HF: Morning p=0.034, Evening p=0.029; AB: Morning p=0.031, Evening p=0.036) and within MIR in which horses had increased enrichment interaction at noon (Morning p=0.029, Evening p=0.0369) and afternoon (Morning p=0.036, Evening p=0.038). Treatments also resulted in horses having a greater number of behavioral differences from control at noon and afternoon, compared to morning and evening. Therefore for better results, owners should prioritize giving enrichment when horses do not have routine meal provisions (likely midday). In summary, providing enrichment positively affects physiology and behavior of stalled horses which may improve horses’ behavioral needs, health, and overall welfare. Further studies are recommended to assess different enrichment items, affective states, and long-term effects.