EFFECTS OF DIFFERENT TOTALS AND RATIOS OF DIETARY CALCIUM AND PHOSPHORUS ON THE PERFORMANCE AND INCIDENCE OF LEG ABNORMALITIES IN MALE BROILER CHICKENS DERIVED FROM NORMAL AND DWARF MATERNAL GENOTYPES

A factorial experiment, with day-old Hubbard male broiler chicks (702 each from Normal and Dwarf maternal genotypes), assessed the effects of three levels of total calcium (Ca) and available phosphorus (aP) at three different ratios (Ca:aP) during the starter (0–21 d) and finisher (22–40 d) periods. General performance was assessed as well as tibia characteristics (strength, ash, Ca, P), serum parameters (akaline phosphatase, Ca, P, Na, K, Cl) and leg abnormalities (tibial dyschondroplasia (TD), twisted legs (TL) and erosion of femoral head (EFH)). Nine starter and nine finisher diets were matched with percentages of Ca and aP ranging from 0.95 to 1.45 and from 0.41 to 0.73 for the starters and from 1.00 to 1.43 and from 0.31 to 0.51 for finishers, respectively. Increasing the total Ca + aP to 2.00 and 1.81 and the Ca:aP ratio to 2.65 and 3.55 for starter and finisher, respectively, reduced (P < 0.05) TD and other leg abnormalities but resulted in the poorest biological response. Ca levels between 1.02% and 1.11% and between 1.05% and 1.14% and aP levels between 0.47% and 0.63% and between 0.35% and 0.46% for starters and finishers, respectively, supported the best biological performance. Higher levels of Ca (1.27%–1.37%) during both the starter and finisher periods resulted in a lower (P < 0.05) incidence of TD and other leg abnormalities but poorer biological performance, particularly for the heavier Normal genotype. Significant genotype × dietary regimen interactions occurred for virtually every measured trait, indicating that these two genotypes (Normal and Dwarf) are metabolically different. Key words: Diet, calcium, phosphorus, ratios, broilers, dwarf, leg abnormalities