The impact of dietary supplementation with zinc and vitamin A on production performance, immune response, blood biochemical markers and carcass characteristics of Japanese quails in a tropical climate

Technical Summary: Impact of Dietary Zinc and Vitamin A on Japanese Quails in a Tropical Climate

Problem Statement
While Vitamin A and Zinc are recognized as essential nutrients for growth, bone and feather development, enzyme function, and disease resistance in poultry, there is limited specific data regarding their optimal dietary requirements and interactive effects in growing Japanese quails (Coturnix japonica). Existing recommendations vary significantly; for instance, Vitamin A requirements range from 1,650 IU/kg (NRC, 1994) to 4,000 IU/kg (Khan et al., 2023), and Zinc requirements range from 25 mg/kg to 90 mg/kg depending on the age and source (NRC, 1994; ICAR, 2013; Abbasi et al., 2017). Furthermore, the interaction between these two micronutrients in the context of a tropical climate, where environmental stressors like high Temperature-Humidity Index (THI) are prevalent, remains under-explored. This study aimed to evaluate the effects of varying dietary levels of Zinc and Vitamin A on production performance, immune response, blood biochemical markers, and carcass characteristics in growing Japanese quails.

Methodology
The study utilized a 2×4 factorial design involving 288 day-old Japanese quail chicks reared over a six-week period (0–6 weeks) in a tropical environment. The birds were distributed into eight treatment groups with four replicates of nine chicks each.

• Dietary Treatments: The experiment tested two levels of Zinc (40 mg/kg and 80 mg/kg) combined with four levels of Vitamin A (1,600, 3,200, 4,800, and 6,400 IU/kg).
• Environment: The study was conducted in a tropical climate where the average Temperature-Humidity Index (THI) ranged from 82.0 to 84.2, indicating a consistently uncomfortable to hot environment.
• Measurements:
  • Performance: Weekly body weight, weight gain, feed intake, and feed conversion ratio (FCR) were recorded.
  • Immunity: Humoral immunity was assessed via Haemagglutination (HA) titre to Sheep Red Blood Corpuscles (SRBC), and cellular immunity via the foot pad index response to Phytohaemagglutinin (PHAP). Spleen, liver, and bursa weights were recorded relative to body weight.
  • Carcass Traits: Live weight, shrinkage, blood/feather loss, dressed weight, and eviscerated weight were measured.
  • Biochemical Markers: Serum levels of total protein, albumin, globulin, glucose, cholesterol, alkaline phosphatase (ALP), phosphorus, and calcium were analyzed.
• Statistical Analysis: Data were analyzed using Snedecor and Cochran's methods, with significant mean differences tested via Duncan's Multiple Range Test (DMRT).

Key Results
The study found that while the interaction between Zinc and Vitamin A levels was generally non-significant for most parameters, the main effects of both nutrients were distinct:

• Vitamin A Effects:

  • Performance: The group receiving 1,600 IU/kg of Vitamin A exhibited significantly lower body weight, weight gain, and poorer FCR compared to groups receiving higher levels (3,200–6,400 IU/kg). Feed intake was not significantly affected by Vitamin A levels.
  • Carcass: The 1,600 IU/kg group had significantly lower dressed and eviscerated weights. Conversely, feather loss was significantly higher at 4,800 and 6,400 IU/kg compared to lower levels.
  • Immunity: The 1,600 IU/kg group showed significantly lower humoral immunity (HA titre), cellular immunity (foot pad index), and relative spleen weight compared to higher Vitamin A levels.
  • Biochemistry: Serum total protein, globulin, and phosphorus were significantly lower at 1,600 IU/kg. Albumin was lowest at 4,800 IU/kg, while glucose was lowest at 3,200 IU/kg. Cholesterol was lowest at 3,200 IU/kg compared to 6,400 IU/kg.

• Zinc Effects:

  • Carcass & Performance: The 80 mg/kg Zinc diet resulted in significantly higher dressed and eviscerated weights compared to the 40 mg/kg diet. However, feather loss was also significantly higher in the 80 mg/kg group. No significant differences were observed in body weight or FCR between Zinc levels.
  • Immunity: The 80 mg/kg Zinc level resulted in a significantly higher relative spleen weight compared to the 40 mg/kg level.
  • Biochemistry: The 80 mg/kg Zinc diet significantly increased serum levels of total protein, albumin, globulin, glucose, cholesterol, and phosphorus compared to the 40 mg/kg diet.

• Organ Weights: Organ weights (liver, gizzard, heart) were not significantly affected by either main effects or the interaction of Zinc and Vitamin A.

Significance and Conclusions
The paper concludes that dietary supplementation levels significantly influence the physiological and productive traits of Japanese quails in tropical conditions. Specifically, the study identifies that a diet containing 80 mg of Zinc/kg and 3,200 IU of Vitamin A/kg is optimal. This combination was found to promote the best balance of growth performance, carcass yield (dressed and eviscerated weights), immune response (spleen weight and antibody titers), and favorable serum biochemical parameters.

The authors note that while higher Vitamin A levels (above 3,200 IU/kg) did not further improve growth metrics, the lowest level (1,600 IU/kg) was detrimental to performance and immunity. Similarly, while 80 mg/kg Zinc improved carcass yield and certain biochemical markers, it also increased feather loss. The study suggests that these specific levels compensate for environmental stress and meet the metabolic demands of growing quails more effectively than the lower or higher extremes tested. The findings support the notion that Vitamin A and Zinc interact to influence nutrient metabolism, with the optimal combination enhancing overall health and productivity without detrimental effects on organ morphology.