Feed restriction and handling of animals destined to be slaughtered have are two factors that affect meat quality negatively. Where handling of slaughter animals is inevitable, fasting is applied to meat producing animals in the ante mortem period to minimise microbial contamination of carcasses or to lower the metabolic rate of certain cattle breeds as an adaptive mechanism to hot climates. From the present study, animals that are historically more docile had higher urinary catecholamine concentrations per se. By quantifying the relationship between catecholamines and animal temperament in cattle, selection of animals with a more favourable catecholamine profile, could enhance the ease of handling slaughter animals and reduce carcass bruising.The difference in urinary catecholamines of three commercial beef breeds types; Brahman, Nguni and Simmental; retained in lairages at an abattoir for either 24 or 3 hours ante mortem was measured. This was done in order to investigate whether longer feed withdrawal periods will lead to increased urinary catecholamine concentrations; a shift in post mortem energy metabolism and negative effects on meat quality.
Catecholamine turnover rate from dopamine to norepinephrine and epinephrine, differed between breed types and feed withdrawal periods. Results indicated a relationship between energy metabolism, feed withdrawal period and catecholamine turnover. Twenty four hours feed withdrawal increased the rate of catecholamine turnover for Brahman and Nguni. Lower early post mortem glycogen together with higher glucose-6-phosphate indicated that glycogenolysis increased for this Brahman and Nguni just before slaughter. Twenty four hours feed withdrawal triggered glycogenolysis via increased catecholamine turnover from dopamine to norepinephrine and epinephrine for Brahman and Nguni. In contrast, feed restriction had no effect on catecholamine turnover. Slightly higher early post mortem glycogen and lower glucose-6-phosphate indicated lower energy metabolism for the Simmental breed type just before slaughter. It seemed as if feed restriction had an energy sparing effect on Simmental type cattle with a consequent negative effect on meat quality.
Warner-Bratzler shear force results were the same among breed types when feed withdrawal was not longer than 3 hours and the values emphasise the importance of providing feed to animals kept in lairages or transported over long distances. When feed is available up until 3 hours before slaughter, irrespective of breed type, meat tenderness was not affected negatively.
When feed was restricted, additional sarcomere shortening and creatine phosphate depletion while the carcass was still warm, occurred to such a degree that the meat from Simmental was tougher. It is clear that feed withdrawal of 24 hours has a significantly negative impact on Warner-Bratzler sheer force of Simmental. In this study with non-electrically stimulated carcasses it is clear that feed must be provided to Simmental up until 3 hours before slaughter to prevent excessive sarcomere shortening and meat toughness. This was explained by a probable lowered metabolic rate and changes in mitochondrial ATP turnover for the Simmental breed type. Cattle from differend breed types react differently to feed withdrawal periods and this knowledge should be applied in the meat industry to assure more consistent meat quality.