Degradation of titin, nebulin, desmin and troponin-T, structural changes in nonstimulated (NS) and electrically stimulated (ES) bovine skeletal muscle and comparison of these changes in Angus x Jersey (AxJ) cattle (Bos taurus cross) with the changes in Brahman x Simmental (BxS) cattle (Bos indicus cross) were determined. Myofibrils for SDS-PAGE and Western blots and intact muscle samples for transmission electron microscopy were prepared at 0, 1, 3, 7, 14 and 28 days postmortem (PM). In SDS-PAGE, ES slightly accelerated the degradation of intact titin (T1 band), nebulin, desmin and troponin-T in AxJ samples. In Western blots of AxJ samples, ES enhanced T1 degradation, the appearance of a 38 kDa desmin degradation product and the accumulation of the 30 kDa polypeptide but had no detectable affect on nebulin degradation. Both SDS-PAGE and Western blots of BxS samples showed that ES had no effect on degradation of T1, nebulin, desmin and troponin-T but slightly enhanced the accumulation of the 30 kDa polypeptide. These four proteins were degraded faster in AxJ than in BxS samples. ES accelerated the appearance of wide I-band fractures and increased the frequency of narrow I-band fractures in all samples and of intermediate and wide I-band fractures through day 7 in AxJ samples. In BxS samples, ES accelerated the appearance and frequency of all three types of I-band fractures through 14 days PM. All three types of I-band fractures were seen sooner in NS AxJ than in NS BxS samples. The frequency of all types of I-band fractures was greater in all AxJ than in all BxS samples. Twice as many intermediate and wide I-band fractures were present at 3, 7, 14 and 28 days in AxJ as in BxS samples. Z-line degradation occurred but was unaffected by ES or by breed. In conclusion, ES slightly accelerated the degradation of titin, nebulin, desmin and troponin-T in AxJ samples only and accelerated the appearance of wide I-band fractures in AxJ samples. ES caused all three types of I-band fractures to appear sooner in BxS than in NS BxS samples.