Stunning bullfrogs by electronarcosis and thermonarcosis: Hematological and plasma biochemical responses

Abstract

Stunning before slaughter should promote the induction and permanence of the animals in a state of unconsciousness to avoid or minimize stress. In bullfrog (Lithobates catesbeianus) slaughter the most used stunning methods are thermonarcosis and electronarcosis. However, little is known about the effect of these two techniques on the bullfrog's welfare. Therefore, this study aimed to evaluate the effect of two different stunning methods on some stress indicators in bullfrogs. A completely randomized design was conducted with four treatments: electronarcosis stunning (4 s inductive shock, 45.5 v and 10 A electrical current with resistive filter), thermonarcosis (saline solution and ice for 15 min, approximately 1 °C), frogs in control condition of their holding pen and frogs restrained in bag (animals placed in a raffia bag for a period of 1 h:30 min). Ten frogs were used as replicates per treatment. Blood glucose, lactate, triglycerides, cholesterol and total protein of frogs subjected to electrical stunning were equal to that of animals kept in holding pen condition. In those stunned by thermonarcosis, there was a reduction in blood glucose and total protein and an increase in lactate, triglyceride and cholesterol and urea, similar to what occurred in frogs restraint in bags. Albumin concentration was higher in animals stunned by electronarcosis and the level of globulins in this treatment did not differ from animals under holding pen conditions. Frogs subjected to thermonarcosis had the lowest concentration of globulins and the amount of albumin was equal to that of frogs in holding pen. The albumin/globulin ratio was higher in frogs stunned by thermonarcosis, compared to the other treatments. The hematocrit and number of erythrocytes were not influenced by the type of stunning. VCM was higher in animals submitted to electronarcosis while hemoglobin, HCM and CHCM was higher in frogs stunned by thermonarcosis. In conclusion, the physiological condition of frogs submerged in ice cold saline solution was as stressful as that of frogs contained in a bag for 1 h:30 min. The electronarcosis stunning technique causes less interference in the hematological and plasma biochemical variables, promoting less stress and, consequently, greater well-being for the bullfrog in the pre-slaughter period. Research is needed to determine if electronarcosis achieves instant unconsciousness.