Abstract: Objective The goal of this work is to study the dark adaptation curve of the normal horse electroretinogram (ERG). Procedures The electroretinographic responses were recorded from six healthy female ponies using a contact lens electrode and a mini-Ganzfeld electroretinographic unit. The horses were sedated intravenously with detomidine, an auriculopalpebral nerve block was then performed, and the pupil was fully dilated. The ERG was recorded in response to a low intensity light stimulus (30 mcd.s/m2) that was given at times (T) T = 5, 10, 15, 20, 25, 30, 40, 50, and 60 min of dark adaptation. Off-line analysis of the ERG was then performed. Results Mean b-wave amplitude of the full-field ERG increased continuously from 5 to 25 min of dark adaptation. The b-wave amplitude peaked at T = 25, however, there was no statistical significance between T = 20 and T = 25. The b-wave amplitude then remained elevated with no significant changes until the end of the study at T = 60 (P > 0.49). The b-wave implicit time increased continuously between T = 5 and T = 20, then gradually decreased until T = 60. No distinct a-wave was observed during the testing time. Conclusions Evaluation of horse rod function or combined rod/cone function by means of full-field ERG should be performed after a minimum 20 min of dark adaptation.

Abstract: REASONS FOR PERFORMING STUDY: Short format 3-day events were introduced in 2004. Anecdotal reports suggested that horses were more tired on completion of the cross-country phase of short format events when compared with horses completing the cross-country phase of long format competitions, despite the absence of Phases A, B and C. OBJECTIVES: To compare the physiological parameters and haematological parameters of horses that had completed the cross-country phase of a short format (SF) and a long format (LF) CCI 2* competition. METHODS: During a CCI 2* competition 69 competitors took part in the short format and 74 in the long format competition. Long format competitors completed Phases A, B, C and D and short format competitors completed Phase D only. Phase D (the cross-country course) was identical for both competitions. Two-way ANOVA for repeated measures and post hoc tests were used to compare temperature, pulse and respiration rates of horses competing in both types of competition. T tests were used to compare mean lactate and electrolyte concentrations, while U-Mann Whitney tests were used to compare CK and AST levels measured in horses competing in the short and long formats of the event. RESULTS: Training schedules, age and previous competition experience were not significantly different between horses competing in the SF and LF competitions. On completion of Phase D, SF horses had significantly higher PCV and significantly lower ionised calcium concentrations when compared with LF horses. LF horses had significantly higher heart rates than SF horses 10 min prior to starting Phase D and immediately after completing Phase D; however, no other significant differences were found between the 2 groups of horses. CONCLUSIONS: Only weak evidence was found to support the hypothesis that the workload for the horse in a SF CCI 2* competition is significantly different when compared to the LF CCI 2* competition. POTENTIAL RELEVANCE: There is no beneficial or detrimental effect on horses that complete short format CCI 2* competitions as compared to those that complete long format CCI 2* competitions but further research is required into the physiological response of horses at CCI 3* and CCI 4* short format competitions.