Effects of different stunning methods on carcass characteristics and the conversion of muscle to meat in commercially farmed Nile crocodiles (Crocodylus niloticus)

Abstract

From the 1950s to the 1960s crocodilians were hunted for their skins, which led to many wild populations being killed. Subsequently, all crocodilians were added to Appendix I or II of the Convention on International Trade of Endangered Species of Wild Fauna and Flora. Restocking wild populations by crocodilian breeding started in 1974, and African countries began showing an interest in commercial crocodilian production in 1984. In South Africa, Nile crocodiles (Crocodylus niloticus) are the preferred species farmed. The crocodilian farming industry mainly produces skins, while meat is the main by-product. Alternative income methods, like meat production, should be considered to increase the feasibility of the industry. There is little knowledge about the conversion of muscle to meat and meat quality in Nile crocodile carcasses. Furthermore, various stunning methods are accepted and used in the commercial crocodilian industry. However, the effect of these methods on crocodilian welfare and meat quality are unknown. This study was conducted to determine baseline values for the conversion of muscle to meat and some physicochemical parameters (i.e., thaw loss, cooking loss, shear force, and fatty acid composition) of farmed Nile crocodiles. This study also assessed the effects of preferred stunning methods on commercially farmed Nile crocodiles’ meat quality. Lastly, this study investigated the effects of different anatomical locations on the conversion of muscle to meat. This study was conducted in May 2023 on a commercial crocodile farm in the Limpopo Province, South Africa. Twenty female Nile crocodiles were stunned and slaughtered from a single pen using two stunning methods (i.e. free bullets and electrical stunning). Carcass temperature and pH measurements and samples for muscle metabolomic analyses were taken from three anatomical locations (i.e. the transversospinalis capitus, longissimus dorsi, and ilio-ischiocaudalis muscles). Samples for the analysis of physicochemical characteristics were taken from the ilio-ischiocaudalis muscle within the tail. Lastly, live weight, blood loss during bleeding, cold carcass weight, and cut weights (i.e., the forequarter, rib casing, hindquarter, and tail tip) were measured. This study showed significant differences in the carcass pH at each time interval between the stunning methods. Significant differences in carcass pH were seen at 6, 9, and 12 hours post mortem between the anatomical locations. Moreover, significant post mortem differences were seen in the glucose and glucose-6-phosphate concentrations between the stunning methods. The anatomical locations showed significant post mortem differences in the glycogen, glucose, and glucose-6-phosphate concentrations. Furthermore, the stunning methods showed no significant differences in the tail meat’s thaw loss, cooking loss, or shear force. This study further showed that the primary fatty acids in the intermuscular and intramuscular fat of the tail are oleic, palmitic, and linoleic acids and that the content of individual fatty acids differ between these tissues. Lastly, a dressing percentage of 61.25% was found, and the tail cut was the highest yielding cut. The results of this study showed that the free bullets stunning method caused less stress than the electrical stunning method. However, the stunning method did not significantly affect the meat quality parameters. Thus, both stunning methods produced similar and acceptable carcass and meat quality. This study further indicated that the tail had a slower glycolytic rate than the neck and body. Thus, the tail may have more slow-twitch muscle fibres than the neck and body.