The effects of a diet supplemented with zinc and vitamin A on production performance, immune response, blood biochemical markers, and carcass characteristics in growing Japanese quails

A study was conducted to assess the efficacy of varying dietary levels of zinc and vitamin-A on performance, immune response, carcass traits, and blood biochemical parameters of growing Japanese quails. The feeding trial lasted six weeks (0–6 wks) and utilized a 2×4 factorial design, incorporating two zinc levels (40 and 80 mg/kg) and four vitamin A levels (1600, 3200, 4800, and 6400 IU/kg). A total of 288-day-old Japanese quail chicks were assigned to eight treatment groups, each with four replicates containing nine chicks. The findings revealed that the group receiving a diet with 1600 IU/kg of vitamin A exhibited significantly (P ≤ 0.01) lower body weight, weight gain, and feed conversion ratios compared to those on higher vitamin A levels during both the 0–5 and 0-6-week periods. However, feed intake did not show significant (P ≥ 0.05) variation across different vitamin A levels during these periods. Additionally, the group on the 1600 IU/kg vitamin A diet had significantly lower live weight (P ≤ 0.01), dressed weight (P ≤ 0.01), and eviscerated weight (P ≤ 0.05) compared to those on higher vitamin A diets. Moreover, feather loss was significantly greater (P ≤ 0.01) at the 4800 and 6400 IU/kg vitamin A levels compared to the lower levels. The diet containing 80 mg Zn/kg resulted in significantly higher feather loss (P ≤ 0.05), dressed weight (P ≤ 0.01), and eviscerated weight (P ≤ 0.01) than the 40 mg Zn/kg diet. Organ weights were not significantly affected by either the main effects or the interaction between zinc and vitamin A levels. Notably, a significantly higher spleen weight relative to body weight was observed at the 80 mg Zn/kg level compared to the 40 mg Zn/kg diet. Significantly (P ≤ 0.01) higher spleen weight in relation to body weight was observed at 80 mg Zn/kg than that recorded at 40mg Zn/kg diet. Significantly lower humoral immunity HA titre to SRBC (P ≤ 0.01), cellular immunity foot pad index to PHAP (P ≤ 0.05) and spleen weight (P ≤ 0.05) in relation to body weight were observed at 1600 IU/kg vitamin A than those recorded at higher levels of vitamin A in the diets. Serum levels of total protein, albumin, globulin, glucose, cholesterol, and phosphorus were significantly higher (P ≤ 0.01) at a zinc intake of 80 mg/kg compared to those at 40 mg/kg. Conversely, at a vitamin A level of 1600 IU/kg, serum total protein, globulin, and phosphorus were significantly lower (P ≤ 0.01) than at higher vitamin A concentrations. Additionally, albumin levels were significantly reduced (P ≤ 0.01) at 4800 IU/kg of vitamin A compared to other vitamin A levels. A significant decrease (P ≤ 0.01) in glucose was noted at 3200 IU/kg of vitamin A compared to 1600 IU/kg, while glucose levels at 4800 and 6400 IU/kg were intermediate. Cholesterol levels were significantly lower (P ≤ 0.05) at 3200 IU/kg of vitamin A compared to 6400 IU/kg, with values at 1600 and 4800 IU/kg being intermediate. The findings suggest that a dietary combination of 80 mg of zinc and 3200 IU/kg of vitamin A is optimal for promoting growth, enhancing carcass yield, improving immune response, and positively influencing serum biochemical parameters in growing quails.