Iron requirements of broiler chickens as affected by supplemental phytase

Abstract

Iron is routinely supplemented in broiler diets intending to prevent dietary deficiencies. The present research was conducted with the objective of assessing Fe requirements of broilers when fed supplemental phytase. A total of 1,280 one-day-old male Cobb x Cobb 500 were distributed in a 2 X 5 factorial arrangement (phytase supplemented diets x 5 graded increases of supplemental Fe) in 80 battery cages, 8 replications of 8 chicks each. The trial was replicated once. Chicks were fed a Fe-deficient diet without phytase (Fe analyzed at 31.30 ± 3.79 mg/kg) from placement to 7 d and then randomly distributed into battery cages with corresponding dieting treatments with or without phytase and graded increases of supplemental Fe. Diets were formulated with corn and soybean meal (SBM), laboratory grade calcium carbonate and phosphoric acid; therefore, the vast majority of dietary Fe originated from corn and SBM (analyzed diet had 53.3 ± 1.41 mg/kg Fe). Phytase was added in excess to the producer recommendation of 1,000 FYT (4,452 ± 487 FYT/kg analyzed) such that phytate degradation was expected to be maximized. Supplemental Fe was from laboratory grade ferrous sulfate heptahydrate (FeSO47H20) which was increasingly added to the diets (analyzed Fe in the supplemented diets were: 53.3 ± 1.41, 65.5 ± 0.59, 77.2 ± 1.97, 87.6 ± 1.72, 97.7 ± 1.33 mg/kg). There were no interactions between phytase and dietary Fe for any response throughout the study (P > 0.05). Supplementing phytase had not effects on Fe intake or Fe excretion, as well as on hematocrit (Ht), hemoglobin (Hb), ferritin, Fe contents in the liver or thigh muscle color (P > 0.05). However, phytase supplemented diets produced better live performance as well as higher ileal digestible energy and Fe digestibility (P<0.05). No effects were found for dietary Fe in live performance at d 28 (P > 0.05). On the other hand, increasing dietary Fe led to linear increases in Fe retention and excretion, Fe contents in livers, as well as Ht and Hb at 14 d (P < 0.05). Quadratic responses (P < 0.05) were observed for Hb at 21d, serum ferritin on d 14, 21 and 28 (maximum responses were 83.3, 104.0, 91.9 and 88.3 mg/kg Fe, respectively). In conclusion, supplementing Fe adding to a total of 97.7 mg/kg dietary Fe did not affect live performance traits. However, the average of Fe related blood parameters was maximized at 91.9 mg/kg dietary Fe. Supplementing phytase provided a significant increase in Fe digestibility.