Factors influencing a malformation of the leg bones of growing chickens
When varying amounts of phosphorus from inorganic sources were added to a basal ration of ground yellow corn, wheat middlings and dry skimmilk, in which the amount of calcium in the various rations was held practically constant, the incidence of slipped tendon increased as the phosphorus increased. Though the trend was very definite, the relation between the amount of phosphorus in the ration and the percentage of slipped tendon was not exactly linear, indicating that factors other than the amount of phosphorus in the ration may have been operating to influence the incidence of slipped tendon. Two groups of chicks fed on the same ration at different times gave very similar growth responses, and though the incidence of slipped tendon was not of the same magnitude, the relation between the numbers of slipped tendon on the various rations remained the same. The lowest amount of phosphorus in this ration which produced slipped tendon was 0.9 percent.
When the amount of phosphorus in the ration was held practically constant at about 1.4 percent and the calcium was fed at levels of 0.34 percent, 1.40 percent and 2.26 percent there were fewer slipped tendons on the low level of calcium than on the medium and high levels. The percentage of slipped tendon on the medium and high levels of calcium was practically the same.
When a basal ration of ground yellow corn, alfalfa leaf meal, dry skimmilk and ground oyster shell was fed about 24 percent of the chicks developed slipped tendon, though the phosphorus content of the ration was only 0.43 percent. With this base, when the phosphorus content of the ration was increased to 1.33 percent by the addition of inorganic phosphorus, the incidence of slipped tendon increased 78 percent. With nearly the same amount of phosphorus, 1.43 percent, a ration containing 20 percent of wheat middlings in place of the alfalfa leaf meal and part of the corn in the above base produced only about 45 percent of slipped tendon. A ration in which the wheat middlings were replaced by rice bran produced no slipped tendon at all.
The percentage of ash in the dry, fat-free femurs, tibiae and metatarsi of chicks afflicted with slipped tendon did not differ significantly from that of the corresponding bones of chicks of the same age on a control ration. The ash of femurs of chicks 10 weeks of age on a ration containing only 0.36 percent of calcium and 0.59 percent of phosphorus was significantly lower than that of chicks of the same age on a control ration, but was not as low as the figures generally given for the ash content of the bones of rachitic chicks. The percentage of ash in the femurs of chicks which received a ration containing 3 percent of magnesium carbonate was significantly lower than than of chicks on the same ration without the magnesium carbonate.