The histological characteristics of meat from 24 bulls of Chianina breed allotted one of two levels of energy (0.94 (A) and 0.76 (B) Meat Feed Units/kg dry matter (MFU) and slaughtered at three ages (8, 12, and 14 month-old) were compared. Muscle samples were collected from the longissimus thoracis (LT) at the 10th rib and from the semitendinosus (ST) at the insertion end and evaluated histochemically for fibre type. Intramuscular fat cells were stained and their diameter determined by image analysis. Muscle fibre types were classified as red (betaR), intermediate (alphaR) and white (alphaW). Intramuscular collagen (IMC) was isolated from LT and ST muscles. Moisture was determined in the same muscles. The fibre size increased from 8 to 14 months, while the percentage of alphaR decreased and alphaW increased with same trend for LT and ST muscles. Level of energy in diet did not significantly affect the fibre size of the two muscles. The percent of alphaW fibres in ST muscle was higher in bulls fed with diet A while the alphaR percentage was higher with diet B in LT muscle. The size of fat cells increased with the age of the animal in both muscles, while IMC and moisture decreased. Diet appeared to have little effect on histological traits and quality of meat, in relation to the amount of collagen and moisture.
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