Relative contributions of hyperplasia and hypertrophy to growth in cattle

The relationship between postweaning DNA accumulation and body weight was calculated for a reference growing steer. Accumulation of DNA (hyperplasia) was calculated from patterns of protein accretion derived from literature data and protein-to-DNA ratios (Pro/DNA) measured in samples of muscles from chuck, round and plate, hides, intestines, rumens and livers of steers slaughtered at body weights ranging from 150 to 700 kg. Amounts of protein relative to DNA found in muscles from chuck, round and plate were used to estimate Pro/DNA changes in carcass. Corresponding values from intestines, rumen and liver were used to estimate Pro/DNA patterns for viscera. This ratio increased in carcass until animals reached body weights of approximately 300 kg and leveled off thereafter. No cell enlargement was evident in viscera. Thus, postweaning protein accretion in carcass results from both cell enlargement (hypertrophy) and DNA accumulation (hyperplasia) until body weights of 300 kg are attained, subsequent growth appeared to be hyperplastic in nature. In viscera, hyperplasia was the primary determinant of protein accretion.