MEASUREMENT OF 24-H GASTRIC PH USING AN INDWELLING PH ELECTRODE IN HORSES UNFED, FED AND TREATED WITH RANITIDINE

A glass combined pH-reference electrode was placed in the stomachs of 5 adult horses and pH was recorded every 6 mins for 24 h while (1) fee d and all bedding materials were withheld for 24 h (unfed), (2) horses had free access to Timothy grass hay for 24 h (fed), and (3) horses h ad free access to Timothy grass hay and were treated with ranitidine, 6.6 mg/kg body weight, orally, every 8 h for 48 h (fed + ranitidine). There was a significant (P = 6.007) difference in median 24-h gastric pH amongst the 3 protocols, the value being 3.1 in fed horses and 1.55 in unfed horses (P = 0.05) and 4.6 in fed + ranitidine horses (P = 0. 05 compared with fed horses). The percentage of pH readings <2.0 was s ignificantly greater (P = 0.05) in unfed (76%) than in fed (30%) horse s, and in fed horses than in fed + ranitidine (9%) horses. The percent age of readings >2.0, 3.0, 4.0, 5.0 and 6.0 were each significantly (P = 0.05) greater in fed + ranitidine horses than in fed horses, and in fed than in unfed horses. There was no difference (P = 0.13) between median gastric pH values from different times of day in unfed horses ( 00:00 to 06:00 h, 1.5; 06:00 to 12:00 h. 1.6; 12:00 to 18:00 h, 1.7; a nd 18:00 to 24:00 h, 1.5). We conclude that gastric acidity is greates t when horses do not have access to feed material and that ranitidine effectively suppresses gastric acidity in horses under conditions of f ree access to hay.