Effect of varying protein and energy levels on growth and nutrient utilization in vanaraja backyard poultry

Introduction

Smallholder poultry farmers in Southeast Asia face a persistent dilemma: commercially formulated feeds boost growth rates but consume 60-70 percent of total production costs, while locally mixed rations based on rice bran and kitchen scraps often fall short of the bird's nutritional requirements [1] . The gap is especially wide for dual-purpose breeds like Vanaraja, which were developed for semi-intensive backyard rearing but can respond well to improved nutrition if the diet is correctly balanced [2] . Vanaraja is a multi-coloured, disease-resistant crossbreed produced by the Directorate of Poultry Research and distributed widely across tropical countries for rural livelihood programs [3] . Under scavenging conditions, Vanaraja birds reach 1.0-1.2 kg at 8 weeks, but this figure can rise to 1.4-1.6 kg with supplemental feeding a 30-40 percent gain that translates directly into household income [4] . The question is how much protein and energy must be supplied to capture that gain without over-investing in feed. Protein is the costliest macro-nutrient in tropical feed formulations, typically supplied through soybean meal, fish meal or sesame cake [5] . Raising CP from 16 to 20 percent increases feed cost by roughly 15-20 percent, so the marginal return in body weight must justify the extra expenditure [6] . Energy density, meanwhile, determines voluntary feed intake through the caloric satiation mechanism: birds on high-energy diets eat less but may deposit more Abdominal fat if the protein-to-energy ratio is unbalanced [7] . The interaction between CP and ME is therefore biologically and economically important but has received limited factorial investigation in Vanaraja specifically. Thailand's tropical climate adds another dimension. Ambient temperatures in Bangkok regularly exceed 33 °C during April-June, which suppresses appetite and diverts metabolic energy toward heat dissipation [8] . Backyard birds with access to shade and scavenging May partially compensate, but the net effect is still a 5-10 percent depression in growth relative to thermoneutral conditions [9] . Optimising dietary density for the hot season is therefore a distinct problem from year-round formulation. The present research aimed to (a) quantify the main and interactive effects of three CP levels and two ME levels on growth performance and FCR in Vanaraja chicks raised under semi-intensive conditions during the Thai hot season, (b) assess nutrient digestibility for each treatment combination, and (c) evaluate carcass characteristics to determine whether increased dietary density altered fat deposition.

Material and Methods

Field Experimental Design

The trial was conducted at the National Institute of Poultry Sciences experimental poultry farm, Bangkok (13.75°N, 100.52°E), from April to June 2023, coinciding with the hotdry season (mean ambient temperature 33.4±2.1 °C, relative humidity 71±8%). A 3 × 2 factorial arrangement was used within a randomised complete block design: three CP levels (16, 18 and 20%) crossed with two ME levels (2650 and 2850 kcal/kg), producing six dietary treatments (T1-T6). One hundred and eighty day-old Vanaraja chicks of uniform body weight (38±2 g) were randomly allocated to 18 pens (10 birds per pen, 3 replicates per treatment). Birds were housed in open-sided pens with rice-husk litter and had access to a fenced outdoor run (2 m² per bird) during daylight hours. Ethical approval was granted by the National Institute of Poultry Sciences Animal Ethics Committee (Protocol NIPS-AEC-2023-007, approved March 2023).

Material

Experimental diets were formulated using maize, soybean meal, fish meal, rice bran, vegetable oil, dicalcium phosphate, limestone, salt, vitamin-mineral premix and DL-methionine. Diets were iso-calcic (1.0%) and iso-phosphoric (0.45% available P). CP levels were achieved by adjusting the soybean meal-to-rice bran ratio, while ME was modulated through vegetable oil inclusion (2% at 2650 ME, 5% at 2850 ME). All diets were analysed by proximate composition (AOAC methods) before the trial commenced. Feed and clean water were provided ad libitum. Birds were vaccinated against Newcastle disease (day 7, live) and infectious bursal disease (day 14, live) per the national schedule.

Methods

Individual body weights were recorded weekly. Pen-level feed intake was measured by weighing offered and refused feed daily. FCR was calculated as cumulative feed intake divided by cumulative body weight gain per pen. A total collection digestibility trial was conducted during weeks 6 and 7: excreta were collected twice daily, pooled per pen, dried at 65 °C for 48 hours, ground and analysed for dry matter, CP, ether extract, crude fibre, nitrogen-free extract (NFE), calcium and phosphorus using AOAC standard procedures. At week 8, two birds per replicate (36 total) were slaughtered by cervical dislocation, de-feathered, eviscerated and weighed for dressing percentage. Abdominal fat pads were excised and weighed. Blood was collected pre-slaughter for serum total protein, albumin, glucose and cholesterol (Erba Chem-7 semi-auto analyser). Data were analysed by two-way ANOVA (CP × ME) with replicate as a random blocking factor using R v4.3; means were separated by Tukey's HSD at p<0.05.

Climatic Conditions

Daily ambient temperature and relative humidity were recorded at pen level using data loggers (Onset HOBO MX2301). During the trial period, mean daily maximum temperature was 36.2±1.8 °C, mean minimum 26.7±1.3 °C, and mean relative humidity 71±8 percent. Heat-stress hours (temperature > 35 °C) averaged 4.2 per day. No mortality attributable to heat stress was recorded, though feed intake depression during the afternoon was noted across all treatments.

Nutrient Budget

Nitrogen balance was calculated for each treatment as nitrogen intake minus nitrogen excreted, expressed per bird per day (g N/bird/d) and as a percentage of intake retained. This provided an estimate of protein utilisation efficiency beyond apparent digestibility alone.

Results

All 180 birds survived the 8-week trial (zero mortality). Mean final body weight ranged from 1124 g in T1 (16% CP, 2650 ME) to 1431 g in T6 (20% CP, 2850 ME), representing a 27.3 percent difference between the lowest and highest treatments. Both CP (p<0.001) and ME (p = 0.008) had significant main effects on final body weight, FCR and total feed intake, while the CP × ME interaction was significant for protein digestibility (p = 0.034) and abdominal fat percentage (p = 0.021) but not for body weight or FCR.

Comprehensive interpretation

Both protein and energy exerted positive effects on growth, but the interaction pattern reveals an important nuance. At the lower energy level (2650 ME), raising CP from 16 to 20 percent increased final body weight by 232 g (a 20.6% gain).

At the higher energy level (2850 ME), the same CP increase produced a 233 g gain (19.4%). The similar absolute gains suggest that the CP effect is largely independent of energy level for body weight, but the significant CP × ME interaction for abdominal fat and protein digestibility indicates that metabolic partitioning does shift: high-energy diets with low protein promote fat deposition, while high-energy diets with high protein channel nutrients toward lean tissue.

Discussion

The 27 percent spread in final body weight between the lowest and highest dietary treatments confirms that Vanaraja birds respond meaningfully to nutritional intensification, even under hot-season stress. This finding agrees with Padhi et al. [4] , who reported a 34 percent body weight advantage in supplemented versus scavenging-only Vanaraja birds in eastern India. But our FCR values (2.61-3.28) are somewhat higher than the 2.2-2.8 range typical of commercial broilers at similar ages, reflecting the inherent genetic ceiling of this dual-purpose genotype [2] . The mechanism behind the improved protein digestibility at higher CP intakes is likely related to substrate availability: when dietary nitrogen exceeds maintenance requirements by a wider margin, a greater proportion of absorbed amino acids flows toward productive functions (muscle accretion) rather than being cycled through urea and uric acid pathways [5] . The CP × ME interaction for protein digestibility suggests that additional energy allows more efficient capture of dietary amino acids, possibly by sparing protein from gluconeogenic diversion [7] . Abdominal fat deposition followed an expected pattern: T4 (16% CP, 2850 ME) recorded the highest abdominal fat at 2.14 percent of live weight, confirming that excess energy without matching protein promotes lipogenesis [6] . This has practical consequences for smallholders: birds sold in liveweight markets face price discounts for excessive fat cover, so the 18 or 20 percent CP formulations are preferable when high-energy ingredients like vegetable oil are included. That said, the cost of soybean meal in Bangkok markets at the time of this trial (approximately 18.5 THB/kg) meant that the T6 diet cost 14 percent more per kilogram than T1. Whether the extra body weight offsets this depends on local live-bird prices, which vary seasonally.

Conclusion

The main contribution of this research is the demonstration that Vanaraja backyard poultry respond to a 3 × 2 factorial combination of protein and energy levels with

Acknowledgement

Acknowledgements Institutional SupportThe authors acknowledge the National Institute of Poultry Sciences, Bangkok, for providing experimental farm facilities, analytical laboratories and climate-monitoring equipment.

References

1. Aini I, Phuoc TH. Smallholder poultry production in Southeast Asia: challenges and opportunities. Worlds Poult Sci J. 2019;75(4):577-590.
2. Haunshi S, Niranjan M, Shanmugam M, Padhi MK, Reddy MR, Sunitha R, et al. Characterization of two Indian native chicken breeds for production, egg and semen quality, and welfare traits. Poult Sci. 2011;90(2):314-320.
3. Padhi MK. Importance of indigenous breeds of chicken for rural economy and their improvements for higher production performance. Scientifica. 2016;2016:2604685.
4. Padhi MK, Chatterjee RN, Haunshi S, Rajkumar U. Effect of age on production and carcass traits of Vanaraja male chickens. Indian J Poult Sci. 2013;48(3):304-308.
5. National Research Council (NRC). Nutrient requirements of poultry. 9th revised ed. Washington (DC): National Academies Press; 1994.
6. Leeson S, Summers JD. Nutrition of the chicken. 4th ed. Guelph: University Books; 2001.
7. Dozier WA, Kidd MT, Corzo A. Dietary amino acid responses of broiler chickens. J Appl Poult Res. 2008;17(2):157-167.
8. Lara LJ, Rostagno MH. Impact of heat stress on poultry production. Animals. 2013;3(2):356-369.
9. Lin H, Jiao HC, Buyse J, Decuypere E. Strategies for preventing heat stress in poultry. Worlds Poult Sci J. 2006;62(1):71-85.
10. Ravindran V, Abdollahi MR. Nutrition and digestive physiology of the broiler chick: state of the art and outlook. Animals. 2021;11(10):2795.
11. Kumari D, Singh RK, Kumar S, Sinha VK. Growth performance and economics of Vanaraja birds under different feeding regimes. Int J Livest Res. 2020;10(6):47-53.
12. Swennen Q, Janssens GPJ, Collin A, Le Bihan-Duval E, Verbeke K, Decuypere E, et al. Diet-induced thermogenesis and glucose oxidation in broiler chickens. Poult Sci. 2006;85(6):957-962.
13. Kamran Z, Sarwar M, Nisa M, Nadeem MA, Mahmood S, Babar ME, et al. Effect of low-protein diets having constant energy-to-protein ratio on performance and carcass characteristics of broiler chickens from one to thirty-five days of age. Poult Sci. 2008;87(3):468-474.
14. Bregendahl K, Sell JL, Zimmerman DR. Effect of lowprotein diets on growth performance and body composition of broiler chicks. Poult Sci. 2002;81(8):1156-1167.
15. Nguyen TTH, Bouvarel I. Environmental impacts of poultry production in tropical systems: a review. J Clean Prod. 2012;28:53-61.
16. AOAC International. Official methods of analysis. 21st ed. Rockville (MD): AOAC International; 2019.
17. Rajkumar U, Rama Rao SV, Raju MVLN, Chatterjee RN. Backyard poultry farming for sustained production and enhanced nutritional security. Worlds Poult Sci J. 2021;77(2):481-496.