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Effect of corticosterone injection on carbohydrate metabolism and tenderness of broiler breast muscle Whalley, Linda Louise

Abstract

The effect of intramuscular corticosterone injection on post mortem muscle metabolism and shear resistance of Pectoralis Major muscle was studied. Short term studies, conducted over an 8 hour post-injection period, showed no significant effect of injection until 6 hours post injection at which time shear values increased from those of the controls. Blood glucose levels rose significantly from 2 to 8 hours post injection. A comparison of shear values of P. Major muscle from 6 week-old broilers and 8 week-old broilers after both had received corticosterone injections showed that the only difference was due to the difference of age not to any alteration in the physiological handling of the injected corticosterone. The greatest difference in treatment effect was found between birds of different stress level. Stress level was subjectively evaluated with respect to the birds reaction to a person entering the range house and to the birds response to handling. Long term studies conducted over 5 and 15 days illustrated homeostatic adjustments to daily corticosterone injections and recovery after cessation of injections. Shear testing was performed on P. Major muscle which was chilled on the carcass and on muscle excised at death. Excised muscle displayed a greater reaction to injection and cessation of injection than did intact muscle due to a lack of skeletal restriction. Shear values decreased on initial injection and increased upon cessation of injection. Homeostatic adjustments returned values to near-normal between these times. Chemical tests were found to display a much more definite reaction to corticosterone injection than did shear testing. Blood glucose and tissue glycogen increased steadily on injection of corticosterone and decreased rapidly at cessation. As expected ultimate muscle pH decreased with muscle glycogen increase. Blood cholesterol increased during injection period as endogenous corticosterone production, for which it is a precursor, was not required.

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