Introduction

Since decades ago, supplementation of methionine and lysine has been successfully used routinely in poultry diets allowing a reduction in CP levels. With the development of additional feed grade amino acids such as threonine and tryptophan, the potential exists to reduce CP even further. However broilers do not seem to perform as well when the intact protein content in diets is reduced to a greater extent and replaced with several EAAs (Bregandahl et al., 2002; Si et al.,2004). Rising corn and soybean meal prices in recent years have resulted in increased feed costs for poultry feeds which forms a major concern in the industry. To alleviate this, several recent studies have focused on the development of dietary formulations aimed at reducing feed costs while maintaining growth and production performance. One such dietary strategy involves formulating diets on an ideal protein basis to provide ideal levels of essential amino acids (EAA) for optimizing growth performance while minimizing excess AA provided by dietary CP. This is accomplished by reducing CP in diets combined with supplementation of limiting AA to their required levels. With a variety of synthetic AA becoming more available and affordable, this feeding strategy is becoming increasingly important in the poultry industry (Burley et al., 2013). Decreasing CP in poultry diets is a good measure to reduce the nitrogen content in excreta and litter as well as reduce ammonia emission which causes respiratory disorders for birds and workers in poultry houses. The recent environmental constraints have forced to base protein/amino acid feeding not only on terms of N retained in animal products, but also in terms of non-utilized fraction of N ingested to protect life from environmental hazards.

The present study with low CP, analyzed blood biochemical profile along with the production parameters in chicks considering that laboratorial blood proofs can help to monitor the variables associated to animal production and nutrition. Babatunde and Pond (1987) attributed decrease in serum total protein to inhibition of protein utilization. Serum level detection depicts the existence of liver cells damage (Aniket, 2005). If liver fails to deaminate amino acids, nitrogenous wastes may accumulate in the body causing deleterious effects. Various reports have affirmed that serum biochemical analyses are important tools to evaluate health and welfare in poultry. Other important function of blood analysis is that it can offer information about body immune system. Although numerous studies in reduced CP diets in commercial strains are reported in the poultry nutrition research sector there is sparse research regarding the supplementation of amino acids in low CP diets in Indian native and improved chicks. Swarnadhara is a backyard poultry strain developed and released by Veterinary College, KVAFSU, Bengaluru and hence this study was undertaken to assess whether supplementing the deficiency of limiting amino acids in reduced CP diets can perform equally in serum parameters with control diet having no CP reduction in the juvenile phase of 0-6 weeks of age in Swarnadhara chicks.

Materials and Methods

The experiment was conducted at the Department of Poultry Science, Veterinary College, Bengaluru. A total of 400 day old Swarnadhara chicks were weighed and distributed in a completely randomized design into five treatments with four replications of twenty chicks in each and were randomly housed in 20 pens in deep litter system. Standard brooding management and vaccination regime were followed throughout the study.

Diet Formulation

The experimental diet was formulated to meet the nutrient requirement specified by ICAR (2013) recommendations for improved native chicken breeds developed in India. The feed ingredients were tested for the amino acid composition as well as for proximate analysis. The treatments consisted of a control diet (T1) based on corn soybean meal formulated with 21% CP and 2800 kcal ME satisfying the ICAR (2013) requirements of first four limiting amino acids at the following levels- methionine-0.46%, lysine-1.10%, threonine-0.70% and tryptophan-0.20% using synthetic amino acids to meet the deficiency. The other treatment diets T2 to T5 were made isocaloric to the control reducing CP content to 20.5, 20, 19.5 and 19%, respectively meeting the amino acid levels as that of control using synthetic amino acids. Tryptophan requirements according to NRC (1994) as well as ICAR (2013) are so meager that there was no necessity for adding synthetic tryptophan in any of the diet. Ingredient composition and analyzed nutrient composition of chick starter diets are presented in Table 1 and 2 respectively.

Table 1: Ingredient composition of chick starter trial diets

DORB- Deoiled Rice Bran , DCP-Di calcium Phosphate; *Mineral Mixture:Each 100g Contains Calcium–32g, Phosphorus-6g, Copper-100 ppm, Cobalt-60 ppm, Manganese-2700 ppm, Iodine-100 ppm, Zinc-60ppm, Iron-120ppm

**Trace mineral mixture: Fe-90000 ppm, I–2000 ppm, Cu–15000 ppm, Mn–90000 ppm, Zn-80000 ppm, Se–300ppm.

***Additives:Vitamin AB2D3-25g, Vitamin B complex-25g, Herbal Liver stimulant-100g; Semduramicin- 30.0g, Tetracyclin- 30.0g, a commercial Toxin binder-100g

Table 2: Analyzed nutrient composition of chick starter trial diets

Table 3: Calculated amino acid composition of chick starter trial diets

Chicks were fed ad libitum with one of the treatment diets from 0-6 weeks. Mortality in respective of experimental group was recorded as and when the birds died. Survivability percentage in each treatment during the course of the experiment was recorded. The dead birds were subjected to detailed post-mortem examination to ascertain the cause of death. On 42^nd day of the trial, blood was collected from the brachial vein into sterile tubes for serum collection and serum collected by centrifugation and was stored at -20 ⁰C for biochemical studies. Serum total protein, albumin, globulin, calcium and phosphorous levels were measured using a biochemical analyzer (Erba chem.-5-plus). The serum antibodies against IBDV were tittered by using indirect ELISA Kit. Each of the steps was followed as per the manufacturer’s instructions. The antibody titer against Newcastle Disease Virus was carried out by using HA followed by HI test.

Statistical Analysis

Data were analyzed using the general linear model ANOVA in a completely randomized design according to procedures described by Snedecor and Cochran (1989). In all cases, significance was set at P< 0.05.

Results and Discussion

Results on immunity and survivability on 42 day cumulative basis are shown in the Table 4. It is evident that CP reduction has no way influenced immunity against ND.

Table 4: Results on immunity and survivability on 42 day cumulative basis

NS-Non Significant, a,b: means along the same column with any identical superscripts are not significant ( p ≥ 0.05)

All the birds exhibited statistically similar values as that of control even with CP reduction because of the balancing of LAA. T2 with 2% CP reduction showed significantly higher titer against IBD but the lowest CP reduced group T5 were showing a similar result as that of control indicating the higher immunity is not really due to a dietetic factor but may be of bird variation because the intact protein content of T2 lies almost close to that of control. These results are in agreement with Saeed (2006) who reported that antibody titres against Newcastle disease virus were not significantly different with respect to different levels of protein. Similar findings were obtained by Santhosh et al., 2012 in Aseel chicken during juvenile phase (0 to 8 weeks) with different protein levels. Thanuja (2013) reported similar findings in IBD titers in the juvenile phase of Giriraja chicks. Hence, this proves that immunity is not dependent on intact protein content or amino acid supply to a greater extent.

Survivability rate remained same throughout the experiment with different diets and proved that CP reduction balancing with amino acids will not affect the health status and welfare of birds during 0-6 weeks of age. The level of incorporation of amino acid found to be adequate to provide optimum disease resistance. The results are in accordance with the findings of Khan et al., 2011 and also Ahmed, 2014, who recorded hundred per cent survivability percentage in a similar study. These results are in par with findings of Manegar (2015) where low CP supplemented with either threonine or tryptophan did not make any difference in survivability rate. The data on serum protein profile of Swarnadhara chicks during juvenile phase is presented in Table 5 which clearly indicates that there is no significant difference among any of the parameters like serum total protein, serum albumin, globulin and albumin globulin ratio. The mean values proved that optimum levels of amino acids are sufficient to maintain normal protein profile in the serum. In a study by Hernandez et al., 2012, reducing the level of protein in the diet of male chicks decreased the plasma albumin levels in the pre starter, starter, and finisher phases. In females, the same effect on plasma albumin levels was observed (P < 0.05) only in the starter phase. The observed decrease in levels of albumin and total protein in plasma in the above study could be related with a deficit of amino acids ingested by the animals justified by Corzo et al., in 2009. But in the present study chicks are straight run and hence this effect is expected to get nullified. These readings are in comparison with findings of Manegar (2015) in low CP amino acid supplemented diets.

Table 5: Results on serum total protein, serum albumin and globulin

NS-Non Significant

From the mean values presented in Table 6, it is evident that the low CP diets with balancing of amino acids did not affect the calcium and phosphorous levels in the serum agreeing with results of Suma (2008). Irrespective of variation in the intact protein profile in the diets, the levels of calcium and phosphorus remained same, might be because of their dietary levels which were uniform among all the five diets.

Table 6: Results on serum mineral profile

NS –Non Significant

This study clearly supports the fact that low CP diets with balanced AA will not impair the immunity and the blood biochemical profile indicating more comfort and reduced heat stress in birds due to reduced protein load and better digestibility of amino acids.

Acknowledgement

This study was supported by the Department of poultry Science, Veterinary College, KVAFSU, Hebbal, Bengaluru, India, with supply of experimental birds and other necessary infrastructure, which is gratefully acknowledged. Author is also thankful to Kerala Veterinary and Animal Sciences University for the deputation granted for Ph.D program.

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