M. Tech. / Purpose: Trigger points in the paraspinal muscles are commonly associated with lameness or stiffness in horses, and unless they are “released”, muscle power and flexibility are impaired and athletic performance is reduced (Rogers, Fischer, Pontinen, and Janssens, 1996). The aim of this study was to determine the immediate and the prolonged effects of Sacroiliac mobilization on spot tenderness within the Erector spinae muscles of performance horses. Method: Horses from a selected stable yard underwent a screening process under the supervision of a qualified Chiropractor and Veterinarian to identify horses suitable for the study. Thirty horses were selected for the study based on the inclusion and exclusion criteria. The sample was divided into two groups of fifteen horses. The experiment group received mobilization therapy for SI joint restrictions, while the control group did not receive any treatment intervention. Procedure: Horses received an initial treatment and two follow ups, totaling three treatments. The first follow up treatment was two days after the initial and the second was four days post initial treatment. During these treatment sessions, trigger points in the Erector spinae muscles were located in each horse and algometer measurements were taken. Sacroiliac restrictions were then identified using motion palpation and passive range of motion as indicators. The researcher performed a mobilization technique on the Sacroiliac joints of horses in the experiment group only, and thereafter both groups were reassessed two minutes later, via an algometer, for spot tenderness within the same trigger points. The Sacroiliac restrictions and trigger points were re-assessed without treatment two weeks later. Conclusion: The results indicated that low-velocity Sacroiliac mobilization was effective in increasing the pain-pressure tolerance within the Erector spinae muscles of performance horses immediately and over the treatment period of two weeks.