Date of this Version
To examine the effects of cimaterol (CIM) and its withdrawal on meat tenderness and carcass composition, 214-old broiler chickens (n = 288) were randomly assigned to one of nine treatments. For Treatments 1 through 6, bids were fed a control diet or a diet containing 1 ppm CIM until slaughter at 35, 42, or 49 d of age. Treatments 7 and 8 consisted of birds fed the CIM diet for 14 d and then withdrawn from CIM for either 7 or 14 d before slaughter (42 or 49 d of age). In Treatment 9, birds were fed the CIM diet to 42 d of age, then withdrawn from CIM for 7 d. Breast muscle (BM) weight, leg muscle (LM) weight, whole body weight, and BM and LM cathepsin B and L activities were obtained on 12 birds/treatment. Body, LM and BM composition and BM shear values were obtained on 12 additional birds/treatment. Eight birds/treatment were used to balance the number of birds per pen. Leg muscle weight, as a percentage of whole body weight, was elevated in CIM-fed birds at all ages, and BM percentage was greater at 35 d of age (P M .05). Leg muscle fat percentage was reduced at 35 and 42 d of age (P < .05), and LM protein was elevated at 42 and 49 d of age (P < .05) in CIM-fed birds. Percentage of protein in the BM of CIM-fed birds was elevated at 35 and 42 d of age. Protein content of the whole body was also increased at 35 d of age. Shear values were higher in 42- and 494-old CIM-fed birds. Withdrawal from CIM increased LM and BM fatness beyond that of controls (P < .05), removed the differences in protein percentage, and removed the detrimental effects on shear value. No differences were found in total cathepsin B and L activities. Broiler chickens fed CIM have increased muscle protein percentage, decreased fat percentage, heavier muscle weights, and reduced meat tenderness. Withdrawal from CIM removed these differences.