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Behavioral Stress and Skeletal Muscle Glycogen Metabolism in Young Bulls

Dunsinea Research Centre, An Foras Taluntais, Co Dublin, Ireland and and University College, Belfield, Dublin 4, Ireland

Abstract

Friesian bulls were penned with an established group of bulls for 6 h. This mixing procedure normally resulted in an intense behavioral interaction between the established herd and each ofthe newly introduced experimental animnals. Muscle needle biopsy samples and blood samples were taken before stress and at intervals during the recovery period. Stressed bulls showed increase over controls in body temperature (P<.001), heart rate (P<.001), serum nonesterified fatty acids (P<.05) and plasma creatine kinase (P<.01). Muscle glycogen content fell during stress to 41% of the value for the control animals (P<.001). On the First day of the recovery period, the glycogen content value, and on d 2 it increased substantially, to 70%. A significant difference existed between experimental and control groups until d 7 of the recovery period. Blood glucose did not differ significantly between the control and experimental groups immediately after stress or during the recovery period. Muscle glucose-6-phosphate was lower in the experimental animals immediately after stress (P<.01) and also on d 1 of recovery (P<.05). Plasma immunoreactive insulin remain close to 40 µunits/ml in both groups, except on the day after stress, when it was below (P<.05) the prestress value. The results show that substantial muscle glycogen breakdown occurred during the period of behavioral stress and that recovery to resting values was a comparatively slow process. It was concluded that the inherently lower blood glucose concentration and insulin activity in cattle than in nonruminant species may reduce glucose availability in cattle and thereby delay muscle glycogen recovery.

¹ Dept. of of Biochem.