Introduction

Poultry is one of the fastest growing segments of the agricultural sector in India today. The growing chickens are inevitably subjected to various kinds of stress that may lead to down regulation of immunity and resulting into outbreaks of infectious diseases. The genetic resistance in poultry is controlled by immune system that plays a dynamic role in health protection; both genetic and environmental factors decide the execution of this role in the bird¹. The immune system is the natural means by which animals resist infection, and immunological parameters may reflect the immune-competence of the immune system and, in turn, the ability of the animal to resists infection. So far, only a few genes have been identified in influencing disease resistance. Genes from the Major Histocompatibility Complex (MHC), involved in antigen-presentation were among the earliest set of genes to be identified. These encode some of the most polymorphic bio-molecules known in the animal kingdom.

This breed has evolved through natural selection in indigenous agro-ecological conditions and is well adapted to the local environment. The Kadaknath birds reveal appreciable degree of resistance to disease compared with other exotic breeds of fowl in its natural habitat in free range. Kadaknath birds are also resistant to extreme climatic conditions like summer hot and cold winter stress and can survive very well under adverse environments like poor housing, poor management and poor feeding.

The immunocompetence status of any breed speaks about its general response to diseases. Resistance to disease is under the control of certain immune response genes. Nucleotide polymorphism in such genes results in variety of pathogens/antigens. The immuncompetence status can be evaluated by assessing important parameters rated to various facets of immunity such as antibody response to SRBC, serum lysozyme activity and serum lgG level etc. Various genetic groups / varieties/breeds/species have also shown significant differences in antibody titers against SRBC, serum lysozyme level and serum immunoglobulin (IgG) level^2,3.

The genetic resistance in poultry is controlled by immune system that plays an important role in maintaining the normal health⁴ and protect from variety of diseases by detecting and neutralizing disease causing agents; both genetic and environmental factors decide the execution of this role in the bird¹. Breeding chickens for higher immunocompetence (IC) and disease resistance provides a viable approach for commercial poultry production. Improvement in disease resistance in poultry by direct selection or by selecting for immune response is hardly feasible due to quantitative nature of disease resistance and/or immune response traits, their low heritability and the difficulties associated with reliable measurements of innate immune responsiveness and resistance to diseases. The objective could be achieved through selecting birds that are resistant against particular pathogens, and/or those displaying better IC, i.e., the general quality of host’s immune system to launch sufficient defence against infections has-been observed in some previous studies, which linked genetic makeup of poultry to disease resistance and/or susceptibility^5,6.

Genetic differences for immune response in chickens have been observed by several workers^7,3. These are currently the subjects of many international studies for determining if the immune responsiveness could be enhanced in a population by selective breeding.

Cell-mediated immunity of chickens has also been examined and demonstrated to be under the influence of genetic origin^7,8. Multitrait immune response selection in egg-type chickens has also been successful^9,10,11,12. Thus, many studies have demonstrated the feasibility of altering immunophysiology by genetic selection.

The immune response to non-specific, natural, multi-determinant, complex and non-pathogenic antigens like sheep red blood cells (SRBC) may provide good indication of natural immune response characteristics, thus resistance is valid for multiple pathogens. The response to sheep red blood cells is T-cell dependent and has association with B-G region of MHC and with one dominant gene of gene complex. The antibody response against SRBC has been widely used to measure the general immunocompetence^{13,14,15,16,7.}

An important reason for breeding for disease resistance is that the genetic improvement is cumulative and can be viewed as one time investment. A major goal in poultry immunogenetics improving disease resistance in poultry by direct selection or by selecting for immune response is hardly feasible due to quantitative nature of these traits, their low heritability and the difficulties associated with reliable measurements of innate immune responsiveness & resistance to diseases.

Genetic resistance of poultry may be improved by selection for immune response to complex non-infectious antigens such as SRBC. Chickens selected for high antibody responses to SRBC showed higher resistance to some infectious diseases, e.g., Marek’s and Newcastle disease virus¹⁷ and coccidiosis¹⁸. Chicken lines divergently selected for antibody response to SRBC revealed a negative correlation between and antibody titters to SRBC¹⁸. Also, selection lines for antibody response to Newcastle disease virus, phyto hemeagglutinin responses, and phagocytic activity showed negative correlation between antibody titters and BW^19. A negative correlation between BW and immune responses might also be based on allocation of limited resources in either direction. According to the resource allocation theory, an individual has a limited amount of resources, which have to be divided over all biological activities, such as growth, reproduction and immune function²⁰. Resources consumed by one of the functions are not available for others. General immunocompetence which is assessed by humoral and cell mediated immunity phagocytic index is important in poultry because birds with better immunocompetence will have better survivability and more resistant to disease. Humoral response to sheep RBC (SRBC) titre is one facet of judging the general immune competence.

Materials and Methods

Chickens

The lines of chickens used in the present study have been previously described^21. In the present investigation, chicks belonging to the selected lines of Kadaknath chickens were used for the study of immunological traits viz., response to sheep RBCs, IgG concentrations. Briefly, chicken lines were used to establish the base population. At hatching, all the chicks were wing-banded and vaccinated against Marek’s disease. They were also administered fowl pox vaccine at 2 wk of age and Newcastle disease vaccine at 2 and 4 wk of age. Chickens of all the lines were provided access to water and a commercial diet.

Experimental animals – Sheep and Kadaknath Breed

Reagents

The important regents of used in the study materials like Alsever’s Solution, which is a store at 4oC. And PBS (Phosphate Buffer Solution), also added 1 Liter Distilled water *pH 7.2.

Collection of Blood

After the 5^th day of immunization of Chickens around 2 ml of blood was collected under the preserved condition in presence of anticoagulant by using 2ml of Syringes.

Haemagglutination test (HA test)

The antibody titer was determined by haemagglutination test (HA) by using Micro liter plates (U bottom). Mercapto ethanol resistant antibodies (MER or IgG) against SRBC.

Experimental Animals -Birds and their genetic background

The current study involved approximate 115 chickens of Kadaknath, randomly selected from a flock of 300 birds being maintained at experimental farm of CARI, Izatnagar, India as a closed flock.

Humoral Response to Sheep RBC

Preparation of Sheep RBC antigen

Approximately 10 ml of heparinized (20 IU/ml) blood was collected from jugular vein of healthy sheep.

Administration of antigen

0.1 ml of 1% sheep RBC suspension was injected into the jugular vein of each bird with tuberculin syringe.

Agglutination Assay

Total and mercaptoethanol-resistant (MER) antibody titers for BA were measured as described by^14. Titers were expressed as the log2 of the reciprocal of the highest dilution in which agglutination occurred.

Estimation of humoral response to NDV         

All the birds were vaccinated against Newcastle’s Disease (ND) at 5^th day with Lasota. Antibody titers against ND were determined by HI assay using 4 HA units of NDV. The highest dilution where there was complete inhibition of agglutination was read as titer^22.

Statistical analysis

Statistical analysis of the data was performed by standard statistical procedure using a computer programme (SPSS package)^23.

Results and Discussion

The observations of current study are listed in following tables and graphs and recorded data was subjected to SPSS 10 software for the establishment of various statistical parameters of indigenous breed Kadaknath. Only chicks immunised on day 12 showed strong humoral IgM and IgG responses, while the other groups appeared not to react to the immunisation. The KN population included either sex wise both male and female, were analyzed for immunocompetence traits. Including the both sex, HA results showed that antibodies titter against SRBCs was recorded with overall mean of 7.69 ±0.14 for purebred KN chickens which are listed in Table No.1.

Graph 1: Graph for IgG.   Click here to View figure

Table 1:  For Ha and IgG Mean for Kadaknath Sex wise.

The BSA-specific IgG response of chicks immunised at 1 day of age was lower and occurred later post immunisation (from 28 DPI) than the response of chick’s immunised at 7 and 12 days of age. In these analyses positive and negative controls were high and very low, as expected, proving that the analyses were executed correctly. These results were proceeding further for statistical analysis to establish significance level and correlation with in group and between the group of male and female. In contrast, strong primary IgG-responses were observed one week later in 21-day-old chicks immunised at 7 days of age but not in 21-day-old chicks immunised at 1 day of age.

 The present finding is supported by several reports of improved antibody response in high line birds selected for immunocompetence^24,25,26. Sheep red blood cells (SRBCs) have been chosen in this study as antigen because they are natural multi – determinant, non-pathogenic antigen and chicken phagocytosis of SRBCs opsonised with FC receptor for lyses and stimulate T-cell dependant response^2,16.  Concluded that immunological memory would to be influenced by genetic selection^27. This was because over-production of antibodies had a negative effect on fitness relative to other traits. Took this reasoning further by challenging these lines and the crosses between them with a range of challenging agents²⁸. Unlike in the previous experiment, high BSA-specific IgG-responses at 14 DPI were already detected in chicks immunised at 7 days of age.

As live vaccines can survive, the possibility exists that antigenic challenge occurs later when the immune system is able to respond. Alternatively, these vaccinations with live, attenuated viruses and expression of their antigens (as membrane proteins on the host cell or associated with host MHC antigens) might accelerate the development of lymphoid structures and prime or activate immunocompetent cells, e.g., by the cytokine-induced up regulation of cell surface ligands. Lines of chickens selected for their ability to produce high antibody to SRBC exhibited higher antibody to Newcastle disease virus, were more resist to Mycoplasma gallisepticum²⁹ and lower mortality rate when they were exposed to Marek’s disease virus³⁰ than the chicken lines that produced low antibody. Therefore, disease resistance may be indirectly improved by selection for immune parameters. The line of chicken selected for humoral response to SRBC antigen responded better to vaccination with viral antigens than a line selected in the opposite direction^18. Demonstrated that the high IgG level was associated with high antibody response to SRBC and lipo-polysaccharides. Also, reported that IgG level was higher for high antibody level than low antibody level^32.

The observation of this experiment is showed various kinds of parameters in the both male and female kadaknath chicken and the statistical analysis to establish significance level and correlation with in group and between the group of male and female. In contrast, strong primary IgG-responses were observed one week later in 21-day-old chicks immunized at 7 days of age but not in 21-day-old chicks immunized at 1 day of age. Analyses show that this increase was mainly due to an increased error variance. Ab titers used in the present study are expressed on a log-scale, but apparently, this scale could not remove all the differences in error variances between lines. As live vaccines can survive, the possibility exists that antigenic challenge occurs later when the immune system is able to respond. This explanation might elucidate why strong IgG-responses were observed in chicks immunized at 7 days of age.

Graph for IgG

Acknowledgement

I am highly thanks full to technical staff.

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