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Influence of Level and Type of Diet on Ruminal pH and VFA, Respiratory Rate and EKG Patterns of Steers

U. S. Department of Agriculture^,2

Abstract

Steers were fed a hay diet and an all-concentrate diet at daily dry matter intake levels equal to 0.5, 1.0, 1.5 and 2.0% of body weight. Ruminal samples collected at 5 hr. after feeding showed that pH, the molar percent of acetic acid and the C₂/C₃ ratio decreased as intake increased and the reverse relationship was obtained for the concentration of total VFA and the molar % of propionic acid. The molar % of butyric acid was significantly lower when the concentrate diet was fed at the 1.5% level. Changes in the ruminal acids due to level of intake were greater when the concentrate diet was fed. Level of intake did not affect the diurnal patterns of ruminal acids or pH except to raise or lower them corresponding to the changes noted when samples were examined at 5 hr. post-feeding. Respiratory rate increased with level of intake and was greater when the concentrate diet was fed. Concurrently, the Q-T segment of the EKG patterns decreased. These physiological changes corresponded to increases in total ruminal VFA and were in the same direction as noted during metabolic acidosis. Heart rate tended to increase at the 2.0% intake level.

¹ The authors gratefully acknowledge the assistance of Annie Rolle and Sid Trump in collecting and analyzing the ruminal samples and Harold Heatwole and Peter Reid in obtaining the physiological measurements.

² Animal Science Research Division, A.R.S., Beltsville, Maryland 20705.

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