Effects of different soybean meals on the incidence of tibial dyschondroplasia in the chicken.

Interexperimental variation in the incidence of tibial dyschondroplasia of chickens that occurred in studies on the effect of dietary calcium, phosphorus and cholecalciferol metabolites was apparent from previous reports from this laboratory. Since the source of commercial soybean meal used in the diets was known to change, studies were conducted to evaluate different sources of soybean meal on the incidence of tibial dyschondroplasia. A series of experiments demonstrated that the soybean meals from one source consistently produced a high incidence of tibial dyschondroplasia (34-69%); whereas soybean meals from a different source consistently produced low incidences (14-28%). This same relationship was found with soybean meals from these two plants produced a year apart. When the levels of two soybean meals that produced a high incidence of tibial dyschondroplasia were reduced in the diet from 35 to 24 12% the incidence of tibial dyschondroplasia was reduced from 60 and 69% to 25 and 20% to 15 and 10%, respectively. The most striking difference between the meals observed by chemical analysis was in the high antitrypsin and urease values of the meals that induced tibial dyschondroplasia. Chickens fed the soybean meal that reduced tibial dyschondroplasia also had reduced pancreas size in one experiment but not another. The soybean meals that induced tibial dyschondroplasia caused an increase in testes size but had no effect on liver, adrenal and thyroid size or plasma levels of calcium, phosphorus and triiodothyronine (T3). No difference in the utilization of the diets as measured by metabolizable energy values and lipid calcium, phosphorus or phytin phosphorus retention was found between the soybean meals that induced high or low incidence of tibial dyschondroplasia with chickens at 19-21 d of age.