Effects of incubation and the trace minerals, zinc and manganese in organic form, on ascites incidence in broiler chickens

Abstract

Recently, intense broiler selection for rate of body weight gain and improved feed conversion has been an area of focus for poultry breeders. Modern broilers achieve slaughtering age at 60% less time than 40 years ago. However, this increased growth rate has resulted in complications that ultimately resulted in metabolic diseases. Pulmonary hypertension syndrome (also known as "ascites") is a very common disease that is caused by an increased metabolic rate due to increased growth rate. Other factors such as incubation conditions, nutrition, lighting programme, altitude and temperature had proven to exacerbate this metabolic disease. Ascites syndrome is characterised by the accumulation of abdominal fluid, liver damage, pericardial effusion and inflammation of the right ventricle of the heart. Zn is responsible for > 300 enzyme processes and is also required for the synthesis of metallothionine that is responsible for antioxidant activity. Mn also operates as a cofactor for superoxide dismutase (SOD) enzymes that provide oxidative stress resistance through formation of non-proteinaceous manganese-based antioxidants. Five thousand eight hundred and eight (5808) eggs from parent stock (Ross 308) were incubated at either normal (37.5-38.0 °C) or high (38.5-39.0 °C) temperatures. Chicks from both these incubation temperatures were randomly allocated to one of four dietary treatments to create a 4x2 factorial design with 8 treatments replicated in 12 pens each. One thousand eight hundred and twenty four (1824) Ross 308 feather sexed males were placed in a 96-pen broiler facility, with each pen (1.5m×1.5m) containing 19 chicks. Four dietary treatments were fed ad libitum from day-old until 42 days of age. Treatment 1 contained 80 mg/kg of ZnSO4 and 80 mg/kg of MnSO4 while Treatment 2 contained 120 mg/kg of each. Treatment 3 contained 80 mg/kg of ZnSO4 and 80 mg/kg MnSO4 and 40 mg/kg Availa Zn/Mn (Zinpro Corporation, Eden Prairie, Minnesota, USA). Finally, Treatment 4 contained 40 mg/kg of ZnSO4 and 40 mg/kg of MnSO4 and 80 mg/kg Availa Zn/Mn. Weekly body weights, feed intake and feed conversion ratio (RCR) were recorded per pen. Daily mortalities were collected, recorded and dissected to determine if the cause of death was attributable to ascites syndrome. At 21 and 42 days of age, two birds per pen were sampled for haematocrit values and necropsied for right ventricle to total ventricle weight (RV/TV) ratios, and ascites syndrome related symptoms. Birds incubated at normal temperature generally performed better than the birds that were incubated at high temperatures. Chicks that were incubated at normal temperatures showed lower mortalities (general and ascites related) and greater carcass weights at the end of the growing period (42 days of age). However, the RV/TV ratios were not significantly different between incubation treatments at all ages. Treatment 1 contained 80 mg/kg inorganic Zn/Mn (sulphates), which represented the lower end inclusion rate of inorganic zinc in poultry diets as an industry standard. Treatment 2 contained 120 mg/kg inorganic Zn/Mn that represented an upper end inclusion rate of inorganic zinc in commercial poultry diets and to observe the level response between Treatment 1 and 2. Treatment 3 contained 80 mg/kg inorganic Zn/Mn and 40 mg/kg organic Zn/Mn, which is the commercial optimum replacement rate of inorganic Zn with organic Zn based on literature to observe performance benefits from organic Zn and Mn. Treatment 4 contained 40 mg/kg Inorganic Zn/Mn and 80 mg/kg organic Zn/Mn, this was to observe any further performance benefits from increasing organic Zn/Mn relative to inorganic Zn/Mn in the diet. Treatment 3 and 4 (Availa Zn and Mn) exhibited improved body weight gain, less mortality (general and ascites related), improved carcass weights, and better flock uniformity at 42 days of age as compared to chicks from Treatment 1 and 2 (ZnSO4 and MnSO4) at the same inclusion levels. The ascites syndrome incidence was also lower in Treatment 3 and 4 as compared to Treatment 3 and 4. These research findings suggest that high incubation temperatures are detrimental to broiler health and welfare and may ultimately increase the incidence of ascites syndrome. However, 40% replacement of inorganic Zn and Mn with their organic sources alleviated ascites incidence and improved overall broiler performance.