Bovine muscle glycogen concentration in relation to finishing diet, slaughter and ultimate pH

The aim of this study was to investigate the effects of a high-energy diet provided for a rather short lime prior to transportation to slaughter on muscle glycogen concentration on farm, after transportation and after refrigeration of the carcasses. The experiment involved 60 Ayrshire bulls which were fed either a low energy diet of 100% grass silage or a compound feed based diet providing 10.8 and 12.9 MJ of metabolizable energy per kg of dry matter, respectively. Identical setup of 30 bulls was carried out ill spring and in summer. Three muscle samples were obtained from the longissimus dorsi and gluteus medius muscles: a biopsy prior to initiation of experimental feeding (B1); another biopsy after 14 days on diet (B2); a post mortem sample at 48 h after slaughter (3) (also M. semimembranosus). Initial resting muscle glycogen concentration affected the responsiveness of glycogen to diet. The more glycogen there was initially the less glycogen increased (r = -0.678, p < 0.0001). However, compared to the low energy diet the high energy diet seemed to protect cattle from potentially glycogen-depleting stressors such as high temperatures and transportation. The cattle on high energy lost 7 +/- 4.0 (se) mmol/kg and 23 +/- 3.9 mmol/kg during transportation in spring cool weather) and in summer (hot weather), respectively, whereas the cattle on low energy diet lost 16 +/- 3.8 mmol/kg in spring and 33 +/- 4.1 mmol/kg in summer. The overall protective effect of high energy diet corresponded to 0.65 pH units. The effects of diet were reflected all the way to ultimate pH values [5.69 +/- 0.03 (high energy); 5.93 +/- 0.03 (low energy)] (p<0.0001) and residual glycogen concentrations (p < 0.0001). It seems indeed that providing a diet high in energy for a couple of weeks prior to transportation to slaughter is one of the many appropriate measures to take in the fight against bovine dark-cutting. (C) 2000 Elsevier Science Ltd. All rights reserved.