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Effects of Stress on Cattle with Hereditary Muscular Hypertrophy¹

University of California, Davis 95616

Abstract

The response of normal and muscular hypertrophy (MH) cattle to the preslaughter stresses of fasting for 48 hr., epinephrine injections or exercise to exhaustion (8.8 km +) was monitored by plasma glucose, blood lactate, plasma urea and CPK concentrations, measured 8 to 16 times during the 2-day experimental period. Four animals of each genotype were subjected to each stress. Fasted MH cattle maintained higher glucose, lactate and CPK. Urea fell during fasting. Epinephrine caused glucose levels to exceed renal threshold and no differences were found. MH cattle had significantly higher lactate and CPK after epinephrine. Exercise caused a small rise in glucose, lactate and CPK in normal cattle. In 2 MH cattle, a catastrophic rise in lactate occurred: one animal died and one would have, had the exercise continued. In all MH cattle glucose, lactate and CPK rose much more than in normal animals. After slaughter MH cattle which had been bled and fasted had muscle pH of 6.2 vs. 5.7 in normal (p<0.05), while fasted MH cattle not subjected to bleeding had final pH of 5.7. Fasting and bleeding summated to stress MH cattle enough to cause "dark cutting." All epinephrine treated animals were "dark cutters." Exercise caused "dark cutting" in one of the 2 MH animals which ran 8.8 kilometers. MH cattle react more adversely to fasting and restraint procedures and to exercise; the dose of epinephrine used was too great to differentiate responses of the two genotypes.

¹ We wish to acknowledge with deep gratitude the generosity of Dr. W. C. Rollins, Department of Animal Science, University of California, at Davis, who supplied the double muscled animals used in this experiment. Dr. Rollins also provided invaluable advice and encouragement.

² Present address: Department of Nutrition, University of Guelph, Guelph, Ontario, Canada.

³ Department of Animal Science.

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