SUMMARYGeneral information on the stunning systems used for horses was collected and 333 horses were observed and scored during slaughter in three slaughterplants in order to evaluate the efficiency of the process, registering: number of attempts required to induce insensibility, presence of return to sensibility signs and stun to stick time; also 100 heads were inspected in order to determine the location of the lesions on the skulls respect to the ideal shooting position. In plant A a non penetrating captive bolt pistol was used, impelled by cartridges with gunpowder; in plant B a penetrating captive bolt pistol was used, that was impelled through a pneumatic system; in plant C the horses were stunned using electricity applied to the forehead by means of a stick with only one electrode at its end. In plants A, B and C respectively, only 76.6%, 78.2% and 2.9% of the horses were stunned at the first attempt, the percentage of horses without signs of return to sensibility was 89.1%, 82.2% and 96.2%, and the percentage of horses that were actually bled within one minute after stunning was 84.4%, 5.0% and 66.3%. When the location of the lesions on the skull was measured respect to the ideal shooting position in plants A and B, it was found that 33.3% and 11.5% of the shots hit the target (within 2 cm). It was concluded that there is a low efficiency in the stunning process of horses and that its main objective, that the animals do not suffer unnecessary pain during slaughter, is not achieved. INTRODUCCIONLos métodos de insensibilización o noqueo tienen como finalidad lograr que el animal quede inconsciente y se mantenga así hasta la muerte, evitando que sienta dolor o molestias al ser sangrado (Wotton 1993); la muerte, que ocurre por pérdida de sangre al seccionar los vasos sanguíneos, debe ocurrir lo más pronto posible después de la insensibilización (Warriss 1996). Otro objetivo, secundario de la insensibilización, es lograr la inmovilidad del animal para disminuir el riesgo de accidente de los operarios. Los procedimientos de insensibilización utilizados en forma correcta provocan en su mayoría insensibilidad inmediata; algunos tienen efecto permanente y otros son reversibles (Gallo 1996). Para evitar el sufrimiento innecesario y mejorar el bienestar de los animales destinados a producir carne se requiere utilizar métodos de insensibilización adecuados (Humane Slaughter Association, H.S.A. 1998, Organización Mundial de Epizootias, O.I.E. 2005). En Chile, el Reglamento de Mataderos (Chile 1994(Chile , 2004) establece la obligatoriedad de insensibilizar a todo animal previo a la faena. El Decreto Nº 342 (Chile 1994) indica específicamente que los equinos deben ser insensibilizados mediante conmoción cerebral, en tanto el Decreto Nº 61 (Chile 2004), que entró a regir en septiembre de 2006 en Chile, es más amplio en este sentido e indica que la insensibilización deberá realizarse sobre la base de mé-todos que atenúen el sufrimiento de los animales y que sean reconocidos internacionalmente, tales como electronarcosi...