PSA Immunology

Broiler starter diets from three commercial feed mills (same company, different locations) were fed to day-old Hubbard Hi-Y broiler chicks along with a Control diet manufactured at Ohio State University. The analyzed calcium levels were as follows: Source 1, .76% ; Source 2, .97% ; Source 3, .81 % ; Control, .98%. Each of the diets was fed to 5 replicate pens of broiler chicks in Petersime battery brooders in each of two light controlled rooms. In Room A, the chicks were exposed to a 24 hr photoperiod from 0 to 4 d and 22 hr from 5 to 21 d whereas in Room B, the photoperiod was decreased to 16 hr at 5 d of age. At the end of the study, each chick was weighed and the tibia and femur were removed for length, width @ 50% of length, defatted dry weight and bone mineral content. Chicks exposed to 16 hr of light weighed significantly less than those chicks exposed to 22 hr (706 vs 747 g; P < .0001). The 16 hr photoperiod also resulted in a significant decrease ( P < .01) in all bone measurements: tibia wt, 1.58 vs 1.78 g; tibia length, 6.34 vs 6.48 cm; tibia width, 5.8 vs 6.0 mm; femur length, 4.82 vs 4.93 cm; femur width, 6.7 vs 7.1 mm. Tibia and femur bone mineral content and bone mineral density were significantly greater in birds fed the Source 2 and Control diets compared with birds fed the Source 1 and Source 3 diets. These same bone mineral measurements were consistently higher in the 22 h. photoperiod though the differences were not always significant. In conclusion, variability in commercial starter diets combined with early photoperiod restriction may have a negative effect on skeletal development in broilers.