ADDITIVE AMELIORATION OF TIBIAL DYSCHONDROPLASIA IN BROILERS BY SUPPLEMENTAL CALCIUM OR FEED DEPRIVATION

Two experiments were conducted to determine the effects of mineral nut rition and early growth rate on tibial dyschondroplasia (TD) in broile r chickens. A com-soybean meal diet with .6% available P (aP) was fed from the day of hatching for 20 days. Experiment 1 had a 2 x 2 x 2 fac torial arrangement of treatments with two dietary levels of Ca (1.1 or 1.8% of the diet), two levels of dietary Cl (.22 or .34%), and two fe eding systems (ad libitum or deprived of feed for 8 h three times per week on Monday, Wednesday, and Friday beginning at 6 days of age). Exp eriment 2 was a 3 x 2 factorial arrangement with three levels of Ca (1 .14, 1.50, or 1.80%) and two feeding systems (ad libitum or deprivatio n as in Experiment 1). Nineteen-day BW gain was not affected by treatm ents in the first experiment. Feed deprivation decreased gain in the s econd experiment, and gain was increased by the highest Ca level witho ut affecting feed efficiency. Feed deprivation did not affect feed eff iciency in either experiment. Dietary Cl level did not affect any vari able studied. Supplemental Ca increased bone ash in the first experime nt, but not in Experiment 2. Feed deprivation and increasing Ca levels decreased the incidence of TD and the amount of severe lesions. Incre asing dietary Ca resulted in a greater accumulation of Ca into the epi physeal growth plate cartilage. The results suggest that the dietary C a:aP ratio required for bone integrity in starter chicks may be greate r than 2.2:1.