A comparison of inorganic and organic sources of zinc to improve bone mineralisation and growth in broilers subjected to high ambient temperatures

Abstract

This study investigated the effects of organic and inorganic Zinc (Zn) supplementation on heat stressed, male Ross broilers. Birds were randomly assigned to 12 treatment groups, consisting of 8 replications each. Each dietary treatment was provided to broilers subjected to either thermoneutral conditions or cyclic heat stress. Dietary treatments consisted of inorganic feed grade Zn sulphate, Availa®Zn (Zinpro Performance Minerals, Zinpro Corporation) or IntelliBond®Z (Micronutrients, Selko, Nutreco). Control treatments comprised of inorganic feed grade Zn sulphate, supplemented at 80 mg/kg and 120 mg/kg inclusion level. Treatment diets contained 40 mg/kg Zn sulphate supplemented with either 40 mg/kg or 80 mg/kg Availa®Zn or IntelliBond®Z. High temperature stress started on day 9 and simulated a cyclic heat wave. Subjecting birds to high temperature stress resulted in significantly (P < 0.05) lighter body weight, lower feed intake and higher FCR compared to birds that were exposed to thermoneutral conditions. Birds supplemented with organic Zn presented with significantly (P < 0.05) heavier body weights and higher feed intakes, compared to inorganic Zn supplemented groups. Hepatic tissues were analysed for total malondialdehyde concentration and total antioxidative capacity at 35 days of age. No significant differences (P > 0.05) were found in malondialdehyde concentration or total antioxidative capacity between birds supplemented with different Zn sources and inclusion levels, under both temperature treatments. Blood samples were analysed for cholesterol concentration, but no significant differences (P > 0.05) were observed between birds supplemented with different Zn sources, at both inclusion levels and temperature treatments. Tibial samples were analysed for dry matter percentage, ash percentage, Zn concentration in bone ash (mg/kg tibia ash) and Zn concentration in dry bone (g/kg dry tibia). Dry matter and ash percentage were not significantly affected by Zn source or Zn inclusion level. Birds supplemented with Availa®Zn presented with the highest concentrations of Zn in bone ash. Broilers presented with significantly (P < 0.05) higher tibia ash concentrations when organic, rather than inorganic, Zn were supplemented at 120 mg/kg inclusion level. The same was observed in Zn concentration in dry bone. Zn concentration in dry bone was the highest in birds supplemented with Availa®Zn and the lowest in Zn sulphate supplemented birds. At 120 mg/kg inclusion level, under both temperature treatments birds presented with significantly higher (P < 0.05) Zn concentration in bone. From our results we concluded that broilers supplemented with organic Zn, at 120 mg/kg inclusion level, offered a feasible, inexpensive way to alleviate the effects of hyperthermia and the performance losses associated with heat stress prevalent in sub-Saharan countries.