This study was part of a larger study to develop an animal production model to obtain the optimum beef tenderness. There is a variety of different beef production systems being used in South Africa. The production systems investigated in this study were; animals reared on pasture until A age classification group (AP), animals reared on pasture until AB age classification group (ABP), animals reared on pasture until B age classification group (BP), animals reared at a feedlot until A age classification group (AF) and animals reared at a feedlot until AB age classification group (ABF). These production systems affect a wide range of components in the muscle that contribute to meat quality. Meat quality refers mainly to tenderness and colour. Scientists and industry role players are uncertain of which production system is the best to produce high quality meat. The aim of the study was to determine the effects of different production systems on the post slaughter muscle energy metabolism and the related effects on meat quality (tenderness and colour). In the experiment 180 steers of the following breed crosses were used: Nguni, Simmental and Brahman. These animals were reared until they reached the A, AB or B age classification, either on pasture or in a feedlot (B only on pasture). All the carcasses were electrically stimulated for approximately 15 sec, before analyses were done. The following properties were measured on the animals after slaughter: tenderness (Warner-Bratzler shear force), carcass pH, carcass temperature, sarcomere lengths, myofibrillar fragmentation length, calpain activity, muscle lactic acid concentration, muscle glycogen concentration, muscle ATP concentration, muscle glucose-6- phosphate concentration, muscle creatine phosphate concentration, muscle glucose concentration, water holding capacity, drip loss and meat colour. These measurements and determinations were done according to standard laboratory procedures at the ARC (Agricultural Research Council) at Irene. Breed had no effect on the muscle energy status for muscle glycolytic potential, muscle lactic acid concentration, muscle glucose concentration, muscle glycogen concentration, muscle glucose-6-phosphate concentration, muscle ATP concentration and creatine phosphate concentration (p>0.05). Older animals from the pasture had lower muscle energy levels than younger animals from the feedlot. Animals from the BP production system had the darkest colour meat with the highest hue angle. AF production system animals had the lightest colour meat with the lowest hue angle and the highest chroma. ABF production system animals had the lowest chroma. Animals from the ABF production system had the lowest shear force value at 1, 7 and 14 days post mortem and animalsfrom the AP production system had the highest shear force value at 1, 7 and 14 days post mortem. This study showed that the energy status in the muscle post mortem does not influence the tenderness of the meat nor the colour (p>0.05). Shear force had a weak to medium positive correlation with muscle pH (between 0.186 and 0.410) and a weak to medium negative correlation with muscle temperature (between -0.157 and -0.268) (p<0.05). Muscle lactic acid concentrations (between -0.033 and -0.322), muscle glucose concentrations (between -0.066 and -0.155) and sarcomere length (between -0.276 and -0.326) had a weak to medium negative correlation with shear force (p<0.05). Muscle glycogen concentrations (between 0.026 and 0.166) and myofibrillar fragment length (between 0.248 and 0.447) had a weak to medium positive correlation with shear force (p<0.05). Shear force had a weak positive correlation with calpastatin activity (between 0.064 and 0.253) and a weak to medium negative correlation with calpain I activity (between -0.183 and -0.313) (p<0.05). The ratio of calpastatin: calpain I (between 0.323 and 0.348) and the ratio of calpastatin: calpain I + II (between 0.183 and 0.275) had a weak to medium positive correlation with shear force (p<0.05). Breed had no effect on the muscle energy status for muscle glycolytic potential, muscle lactic acid concentration, muscle glucose concentration, muscle glycogen concentration, muscle glucose-6-phosphate concentration, muscle ATP concentration and creatine phosphate concentration (p>0.05). If electrical stimulation was not used in this study the difference between the production systems in terms of muscle energy status and colour would have been more prominent. The conclusion is that if animals are slaughtered under “ideal” circumstances in terms of stress being kept to a minimum before slaughter and the carcasses are electrically stimulated in order to prevent cold shortening, the production system shows a small effect on the energy status of the animal and consequently also levels out the meat quality characteristics such as tenderness and colour. For more dramatic results and academic value it would have been more useful to include more variations of non-ideal slaughter conditions and non-electrical stimulation, as well as more breeds. A follow up study with no electrical stimulation can be helpful to explain some uncertainties. This follow up study will present its own challenges, for example higher frequency of DFD. A follow up study on the effects of a larger variety of breeds can help to determine the exact effect ofmuscle energy metabolites in the different breeds, on the tenderness and colour of the meat. Copyright
Dissertation (MSc(Agric))--University of Pretoria, 2012.