Effects of protein deficiency on the mRNA levels of insulin‐like growth factors and myostatin in skeletal muscle of weaned lambs

Abstract

ABSTRACTWe investigated the effect of protein deficiency on mRNA levels of insulin‐like growth factors (IGF‐I and ‐II) and myostatin in skeletal muscle of weaned lambs. Weaned lambs were given a control diet (crude protein, 18%) or a low protein diet (crude protein, 5.7%) for 20 days. A small piece of the M. longissimus thoracis was collected by surgical biopsy at the end of feeding trial. The mRNAs of IGFs and myostatin were determined using a real‐time reverse transcription polymerase chain reaction. Blood samples were also collected to measure plasma concentrations of IGF‐I and serum urea nitrogen. Control lambs gained normally, whereas the bodyweight of the animals given the low protein diet was maintained and was significantly lower than that of the control from 10 days of the onset of feeding trial. Protein deficiency affected neither IGF mRNAs nor myostatin mRNA in the muscle. The expression of these mRNAs was unlikely to respond sensitively to protein deficiency in the muscle. However, serum IGF‐I concentration was significantly lower in the protein deficient lambs than in the control animals. Therefore, we consider that the retardation of muscular growth does not depend on the local mRNA expression of these factors in protein deficient lambs, but the reduction of serum IGF‐I, at least, partly contributes to the suppression of growth.