Abstract
Cross-bred chicks of White Cornish male and New Hampshire female were fed one of nine experimental diets. Each experimental diet contained the same amount of nutrients except calcium and phosphorus and contained one of the combinations of 3 levels of calcium, i.e. 1.2, 1.0 and 0.8%, and of 3 levels of phosphorus, i.e. 0.8, 0.6 and 0.4%.
In Expt. 406, growth rate of day-old chicks on the diets of low phosphorus (0.4%) was significantly slower than those on diets of higher phosphorus levels than 0.4%. Two chicks on the diet of 0.4% phosphorus and high calcium of 1.2%, died during the initial 3 weeks. The x-ray examination of the left leg of the chick on this diet revealed that the tibia was bent as shown in left part of Photo. 1 and that the both ends of the femur and the tibia were obscure in contrast with the x-ray photograph of normal bone shown in right part of Photo. 1. Curved ribs were also observed by the post-mortem examination. These symptoms indicated the richet and mal-calcification.
At 3 weeks of age one male and one female chick from each lot were selected at random and sacrificed for tibia ash analysis. Tibia ash content of chicks on the diets of low phosphorus (0.4%) was significantly lower than those of chicks on the diet of higher phosphorus level. The rest of the chicks in each lot were reared until 8 weeks of age. Although body weight of chicks on the diets of 0.4% phosphorus was smaller than those on the other diets, they grow fairly well and no chicks died after 3 weeks of age.
Expt. 411 was designed to confirm the previous findings that chicks older than 3 weeks can grow normally on the diets of 0.4% phosphorus. Four-week-old cross-breds were grouped into 9 lots and fed one of experimental diets as in Expt. 406. Growth rate, feed efficiency, and tibia ash content at 10 weeks of age were almost identical among the chicks on 9 diets.
It was suggested from these experiment that dietary levels of 0.8% for calcium will be satisfactory for growth of broiler chicks and that dietary level of 0.6% for phosphorus will be enough for chicks younger than 4 weeks, although 0.4% may be satistactory for older chicks.
Since the diets of 0.4% phosphors contained only 0.05% of inorganic phosphorus and the rest was plant origin, chicks older than 4 weeks looks like to have ability to utilize plant phosphorus with high efficiency.
