Graduate Thesis Or Dissertation
 

Electrocardiograms and related variables of dwarf beef cattle

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  • Electrocardiograms from 12 compressed male (CM), 16 compressed female (CF), ten synthetic compressed female (SCF), nine brachycephalic female (BF), and 15 dolichocephalic female (DF) dwarfs from Davis, California, taken in the scapular lead S-II (prescapular position positive and right forelimb negative) were analyzed, The data on dwarf electrocardiograms were compared with normal Hereford cattle data obtained by Van Arsdel and Manning at Corvallis, Oregon. The average R-R, P-R, Q-T, and T-Q intervals, and the QRS duration did not differ among the dwarf subgroups. The average R-R, P-R, Q-T and T-Q intervals were 0.73, 0.20, 0.35, and 0.39 second, respectively, in dwarfs. These were significantly longer than the average intervals of 0.63, 0.16, 0.32 and 0.30 second, in normal Hereford cattle of Manning. Average QRS duration in dwarfs was 0.07 second and was near 0.08 second in normal Herefords found by Manning. The P, QRS and T wave forms of dwarfs did not differ specifically from those found in normal Hereford calves. The directions and potentials along P, QRS and T axes were determined from analysis of leads S-I (left forelimb position positive and right forelimb position negative), aVF (left hind limb connection positive and pooled right forelimb and left forelimb connection negative), and S-aVF (pre scapular position positive and pooled right forelimb and left forelimb connection negative). The average P-axis potentials of CM, CF, SCF, BF and DF dwarfs were 0.25, 0.29, 0.31, 0.32, and 0.35 millivolts, respectively; the average QRS-axis potentials were 0.91, 0.78, 0.85, 0.89, and 0.96 millivolts; and the average T-axis potentials were 0.34, 0.46, 0.54, 0.54, and 0.59 millivolts. The P-axis potentials of dwarfs were frequently higher than those for normal Hereford cattle reported by Van Arsdel. The average QRS-axis potentials of dwarfs ranged from 0.40 to 1.43 millivolts, while those of normal Hereford cattle of Van Arsdel ranged from 0.58 to 1.48 millivolts. The T-axis potentials of dwarfs ranged from 0.22 to 0.88 millivolts, while those of normal Hereford cattle of Van Arsdel ranged from 0.22 to 0.85 millivolts. The CF dwarfs had significantly lower average P, QRS and T potentials than did DF dwarfs. The P and T axis potentials were significantly lower in CM than in CF, SCF, BF and DF dwarfs. The P axes pointed ventrad, caudad and sinistrad in most dwarfs. The cones of the directions of P axes of CM, CF, SCF, BF, and DF dwarfs overlapped, and differences between cones were not marked. The P axes of the normal Herefords of Van Arsdel also pointed, in general, ventrad, caudad and sinistrad. The QRS axes were oriented cephalad, dorsad and sinistrad in the majority of the CM and CF dwarfs. The QRS axes of SCF, BF and DF dwarfs were oriented cephalad or caudad, dorsad, and dextrad or sinistrad. The T axes pointed ventrad, cephalad and dextrad or ventrad, caudad and sinistrad in most dwarfs. Differences among T axes of the dwarf subgroups were not marked. The T axes were oriented dextrad in 46 percent of the dwarfs and in 92 percent of the normal Hereford cattle of Van Arsdel. The average QRS/P angle was 141, 140, 128, 121, and 112 degrees in CM, CF, SCF, BF, and DF dwarfs, respectively, and was significantly higher in CM and CF dwarfs than in BF and DF dwarfs. The QRS/P angle ranged from 72 to 171 degrees in dwarfs and from 73 to 180 degrees in the normal Herefords. The average QRS/T angle was 130, 133, 145, 146, and 140 degrees in CM, CF, SCF, BF, and DF dwarfs and was not significantly different among dwarf subgroups. The QRS/T angle ranged from 94 to 172 degrees in dwarfs and from 91 to 178 degrees in the normal Hereford cattle of Van Arsdel. The P, QRS and T vector loops were obtained in the S-plane in seven SCF, six BF and eleven DF dwarfs. The differences among the loops were not marked.
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