Zeranol and Dietary Protein Level Effects on DNA, RNA and Protein Composition of Three Muscles and the Relationship to Serum Insulin and GH Levels of Steers

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Abstract
The effects of zeranol and dietary protein level on DNA, myofibrillar, sarcoplasmic, non-protein, and stroma protein N concentrations in the longissimus, adductor and intercostal muscles of 36 steers were determined. Certain correlations of plasma GH and insulin levels with these characters were also determined. Nuclear Feulgen-DNA and sarcoplasmic Azure B-RNA values were obtained by standard plug microspectrophotometry. Significantly (P<.01) lesser amounts of NPN and sarcoplasmic protein N and greater amounts of stroma protein N were observed in inter-costal vs. longissimus and adductor muscles. Also, inter-costal muscle averaged significantly greater for percent lipid and less for percent water than did either of the other muscles. Mean DNA values were depressed in inter-costal vs. adductor muscles while RNA values were elevated in inter-costal as compared to longissimus and adductor muscles. The only significant treatment effect was an increased percent water and decreased percent lipid in longissimus samples of implanted steers, and a zeranol X; dietary protein level interaction (P<.05) on DNA values. The implanted 11% protein group had depressed DNA values as compared to all other groups except non-implanted 9.5 and 12.5% protein groups. GH levels were significantly (P<.05) correlated at day 84 with RNA for inter-costal muscle (r=−.43), at day 139 with NPN of inter-costal muscle (r=0.37) and at day 169 with stroma protein N of inter-costal muscle (r=0.45). Copyright © 1973. American Society of Animal Science . Copyright 1973 by American Society of Animal Science

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