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Influence of Type and Level of Grain and Diethylstilbestrol on the Rumen Microbial Populations of Steers Fed All-Concentrate Diets

U. S. Department of Agriculture, Beltsville, Maryland

Abstract

Steers were fed ad libitum all-concentrate diets which contained either 90% corn or 90% wheat in two trials. All concentrate diets which contained 90% milo, barley, corn or wheat were fed at 1.5% of body weight daily in a third trial. Results indicate that regardless of whether steers had been implanted with diethylstilbestrol (DES) or not, the same major groups of ruminal bacteria were present as determined by Gram-smears and by presumptive identification. Increased gains of cattle caused by DES implantation were not associated with ruminal protozoal number increases. In one trial protozoa were not detected in the majority of the steers regardless of whether DES was implanted or not. Some bacterial differences were noted between the three trials. Among the ruminal bacteria which were isolated from steers fed ad libitum, 82 to 95% hydrolyzed starch while none hy-drolyzed cellulose. Restricted feeding increased both the number of protozoa and cellulolytic bacteria over that of steers fed the same diets ad libitum. Steers fed milo contained less ruminal DNA, lactobacilli and viable bacteria than steers fed corn, barley or wheat. Within the limits of changing the grain portion of the diets, there appeared to be more variation in the ruminal microbial population between animals fed the same diet than there did between groups of animals fed different diets.

¹ A.R.S. Animal Science Research Division, Beltsville, Maryland 20705.

² Present address: Pathological Service, U. S. Walson Army Hospital, Fort Dix, New Jersey 08640.

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