resistance and their impact on survival rate

Aim: This study was aimed to develop the disease resistance broiler chicken lines over two generations (G , G and G ) of 0 1 2 selection for immunocompetence (IC) index by targeting all the facets of immune response traits viz., humoral response (HR) to Sheep red blood cells (SRBC), cell mediated immune response (CMI) to phytohaeagglutinationP mitogen (PHA-P), levels of serum serum immunoglobinG (IgG) and serum lysozyme (LZM) level. Materials and Methods: The SDL Synthetic Dam Line (SDL) broiler line consisting of 303, 204 and 300 birds in G , G and 0 1 G generations, respectively were screened for immunocompetence traits such as humoral response to SRBCs, cell mediated 2 immune response to PHA-P and levels of serum lysozyme by Lysoplate assay and IgG by SRID method, and ranked based on their IC index values. Results: The percent survival rate up to 6 weeks of age in SDL broiler chicken lines were selected for high immunocompetence index (HIC) and low immunocompetence index values (LIC) over two generations (G , G and G ) of selection 0 1 2 and observed that significant differences (P< 0.05) in percent survival pattern in the base population (n= 303) with the highest survivability of 100.00% was observed in 5-6 weeks of age followed by 99.37% and 97.23% in 4-5 and 0-4 weeks of age respectively. In the G generation, significant differences ( P<0.01) was noticed in the selected high and low index lines up to 6 1 weeks of age with the overall survival rate lower in high index lines (93.10% ) as compared to the low index lines (97.62%). Whereas the reverse trend was observed in the G generation that the high index line had significantly (P<0.05) higher survival 2 percent (98.62%) as compared to the low index lines (97.93%). Moreover, the overall survival rate was better substantially over the two generations of divergent immunocompetent index selection of SDL broiler chicken lines. The present investigation revealed that breeding for better immunocompetence status by selection index could lead to better health status in term of improved survival rate in broiler chicken over the generation of selection and further suggested that index selection for more number of generations coupled with economic traits would seem to be a viable option for development of disease resistant chicken lines. Conclusion: Breeding for overall genetic improvement of immunocompetence status by index selection with all the facets of immune system could lead to better survival rate and development of disease resistant chicken.


Introduction
broiler breeding programme therefore should give due consideration to the general health status of the birds. Mortality has always been a great concern in Conventional vaccination program coupled with the poultry flocks. Re-emergence of the poultry diseases modern managemental practices strive to protect the cause huge losses to the poultry industry. It is desirable birds from many pathogens. However, the lapses at to have disease resistant strains having better genetic various levels and/ or the change in pathogenicity of combination in association with beneficial traits, for causative agents, development of resistant strains of increased fitness to the subsequent generations. In case pathogens, medicinal treatments are often ineffective of natural selection, genetic improvement is slow but causing severe economic losses, which necessitate the constant; whereas in artificial selection, the genetic need for improving the genetic resistance [6]. Genetic improvement for single or more traits will bring about variability exists in chickens for immune response to noticeable improvement in few or more generations specific antigens [7-8], allowing for moderate genetic [1-2]. Immunity for disease resistance is a complex response to selection for both increased and decreased genetic trait that is multifaceted [3]. Selection based on titer [9-10] and considerable evidence of polygenic an index, combining several immunocom-petence inheritance of humoral and cellular immunity in traits seems a viable preposition [4][5]. The modern responses to selection for antibody response to various antigens. Multiple genetic factors have been found to affect the immune response and disease resistance in chicken [11]. Hassan et al [12] compared the effects of selection for immunocompetence (IC) index by targeting all the facets of immune response traits viz., humoral response (HR) to Sheep red blood cells (SRBC), cell mediated immune response (CMI) to phytohaeagglutination-P mitogen (PHA-P), levels of serum serum immunoglobin-G (IgG) and serum lysozyme (LZM) level.

Materials and Methods:
The SDL Synthetic Dam Line (SDL) broiler line consisting of 303, 204 and 300 birds in G , G and 0 1 G generations, respectively were screened for immunocompetence traits such as humoral response to SRBCs, cell mediated 2 immune response to PHA-P and levels of serum lysozyme by Lysoplate assay and IgG by SRID method, and ranked based on their IC index values.

Results:
The percent survival rate up to 6 weeks of age in SDL broiler chicken lines were selected for high immunocompetence index (HIC) and low immunocompetence index values (LIC) over two generations (G , G and G ) of selection 0 1 2 and observed that significant differences (P< 0.05) in percent survival pattern in the base population (n= 303) with the highest survivability of 100.00% was observed in 5-6 weeks of age followed by 99.37% and 97.23% in 4-5 and 0-4 weeks of age respectively. In the G generation, significant differences ( P<0.01) was noticed in the selected high and low index lines up to 6 1 weeks of age with the overall survival rate lower in high index lines (93.10% ) as compared to the low index lines (97.62%). Whereas the reverse trend was observed in the G generation that the high index line had significantly (P<0.05) higher survival 2 percent (98.62%) as compared to the low index lines (97.93%). Moreover, the overall survival rate was better substantially over the two generations of divergent immunocompetent index selection of SDL broiler chicken lines. The present investigation revealed that breeding for better immunocompetence status by selection index could lead to better health status in term of improved survival rate in broiler chicken over the generation of selection and further suggested that index selection for more number of generations coupled with economic traits would seem to be a viable option for development of disease resistant chicken lines.

Results and Discussion
infection with Newcastle disease virus and infectious bursal disease virus on four Egyptian chicken breeds The percent survival rates of SDL broiler chicken lines up to the market age (6 weeks) were selected for high and low immunocompetence index by combining HMI, CMI, IgG and LZM traits over two generations Survival rate under (G , G and G ) of selection are presented in table 1. 0 1 2 selection for improvement of an immunocompetence Significant differences at 5% (P<0.05) in percent status in broiler chicken lines are not well studied and survival pattern was observed between the ages at 0-4, very scanty information is available using immuno-4-5 and 5-6 weeks of age with 97.23%, 99.37% and competence index selection.
100% respectively, thus indicating that the survival rate Keeping the above in view, the present investiis influenced by different genetic and environmental gation is aimed to fill this gap in knowledge by factors such as feed, water, vaccination, exposure and studying the overall natural survival patterns of the or outbreak of diseases, stress and genotype x phenodivergently selected broiler chicken lines for improved type interactions etc [13]. Moreover, the higher survival immunocompetence status over two generations. rate was noticed in the market age at 5-6 weeks of age

Materials and Methods
as compared to the initial period, indicating that the immunity development is not fully developed in very Ethical approval: The present study was approved by young chicks [14]. Moreover, the overall increase in the survivability of screened for various immunocompetence traits, using the selected lines over two generations of divergent protocols reported earlier [5]. All the birds were ranked selection at all the weeks of age showed a positive on the basis of IC index constructed by combining correlation with the direction of selection in favor of these traits by giving equal economic weightage to all high IC-index lines as compared to the low lines. As these traits. About 5-6 males and 30-36 females at the per the expectation, the present findings also revealed high and low index values birds were chosen as parents that the higher immunocompetent status chicken lines of G high immunocompetence index (HIC) and low 1 show better survivability as compared to the lower immunocompetence index values (LIC) index lines, lines and had almost more than 99.00% survival rate respectively. The selected high and low lines were bred was observed from 5 weeks of age indicating that the within the lines by artificial insemination and produced possibility of passive development of immunity begins first generation (G ) offspring. In G generation, 92 1 1 after 4 weeks of age coupled with maternal antibodies chicks in high and 112 in low IC index lines were [14]. Similar to the present study, previously studies obtained. Similarly, parents of G generation were 2 have been reported for long-term selection experiments selected in the respective lines and 152 and 148 chicks to single antigen such as Sheep RBC (SRBC) [4], for of high and low IC-index lines, respectively were immune response to IBDV vaccine [15], for immune obtained in G generations for this study. Details on 2 response New Castle Disease vaccine [5] and for incubation and hatching, vaccination, management Marek's Disease Virus [16] and for immune response and feeding etc. are reported previously [5].
E.coli [17], that had resulted in significant differences in immune responses and viability between the infectious bursal disease virus on four Egyptian 6 weeks of age. Post Mortem inspection was conducted chicken breeds, and found that Mandarah chickens (a at Veterinary Pathology Department, Indian Veterinary dual purpose breed developed through cross-breeding) Research Institute, Izatnagar, UP to find the cause of showed less susceptibility than the other breeds to both the death. The survival rate of the healthy population diseases, indicating significantly higher survival rates was also recorded for the developed lines without following artificial infection. killing the birds.
The present investigation showed that the overall Statistical analysis: The survival rate in each line was survival rate was improved after two generation of recorded and presented as percentage. The comparison selection in both the lines ( from 93.1 to 98.71 and from between groups was done by Chi square test. 97.62 to 97.93 in high and low lines, respectively) and found that Mandarah chickens showed less susceptibility than the other breeds to both diseases, indicated by significantly lower mortality rates following artificial infection.
( Figure-1). These results were in agreement with immune system such as HMI, CMI, serum IgG and earlier report [18] that reportedan increase in the lysozyme levels, could lead to better health status in general survivability of the chick's belonging to high term of survivability in SDL broiler chicken lines. humoral response line as compared to low line based on Further, the immunocompetence selection index would antibody response to E.coli response. Also it was found be a viable option for the development of disease resistant that a line of birds selected for low immune response chicken lines, keeping in view of the economic traits. was more susceptible to infections from endemic   Comparisons were made among periods in base population, between lines within each period as well as in overall in each generation. Means bearing common superscript do not differ significantly (P<0.05)