This investigation was carried out to study the influence of immunocompetence levels of layers on its economic performance traits after long term selection in Rhode Island Red chicken (selected strain) maintained at experimental layer farm of ICAR-CARI, Izatnagar. Hundred (100) chicks of five weeks age were immunized with 1% (v/v) sterile sheep erythrocytes suspension (SRBC). In vivo antibody response to SRBC, serum lysozyme and serum IgG concentrations were estimated through haemagglutination (HA) test, lysoplate and single radial immunodiffusion assays, respectively and were classified into high, medium and low levels of immunocompetence based on their means and standard deviations. Layer performance data under various immunocompetence levels were analyzed by least squares analysis of variance. The least squares means of HA titre, serum lysozyme and serum IgG concentrations were 9.33±0.34, 4.42±0.18 μg/ml and 8.72±0.41 μg/μl, respectively. Pullets with high serum lysozyme concentration laid highest (P<0.05) number of eggs upto 64 weeks of age followed by those with medium and then low levels of lysozyme concentration. HA titre and serum IgG levels had no significant association with any production traits. The output of this investigation might be useful for the layer breeders when its genetic improvement is concerned for its production and protection status.
Good health and survivability of birds along with optimum productive performance is one of the most important factors for deciding the success and feasibility of poultry production. Development of modern strains of various layers and broilers after long-term genetic selection programs were focused only on high production potentials. Increasing selection pressure on economically important traits in high yielding populations led to severe decline in immune response, which decrease capabilities and increased susceptibility to numerous diseases (Tomar et al., 2012), which in turn impairs genetic improvement in production traits.
Knowledge of disease resistance ability of different breeds or strains of chicken and their association with production performance provides significant information for genetic upgrading of birds with higher production and protection status (Miller et al., 1992). Antibody response to sheep erythrocytes antigen suspension, serum lysozyme and immunoglobulin-G levels are regarded as indicators of birds’ immunocompetence status (Das et al., 2016). Rhode Island Red (RIR) is a dual purpose brown-egger chicken breed, undergone long-term selection for 30 generations on the basis part-period egg production and is being maintained for development of multicolored strains for rural poultry production. The present investigation was undertaken to study influence of immunocompetence levels of layers on its economic performance traits in a selected strain of Rhode island red (RIR) chicken after long term selection (thirty generations) based on part period egg production.
Single hatched out 100 pedigreed RIR chicks of selected strain maintained at experimental layer farm of ICAR-Central Avian Research Institute, Izatnagar were used in this investigation. The birds were maintained under standard managemental and nutritional conditions (Rahim et al., 2016). Five weeks aged chicks were immunized with one ml of 1% (v/v) sterile sheep erythrocytes (SRBC) suspension in PBS (pH 7.4) de novo prepared from Muzaffarnagari sheep breed maintained at experimental Nutrition shed of Indian Veterinary Research Institute, Izatnagar. The hyper immune sera were harvested in 0.5 ml sterile tubes from 1 ml of anticoagulant free blood collected from the immunized chicks on day 5 post-immunization (dpi) and stored at –20°C till further use (Rahim et al., 2015).
The 5 dpi in vivo antibody response against SRBC was assessed by haemagglutination (HA) test (Van der Zijpp and Leenstra, 1980). The maximum dilution (n) of sera that yielded complete agglutination was recorded as titre and expressed as log2n (Siegal and Gross, 1980). The serum lysozyme and serum IgG concentrations were assessed using lysoplate assay (Lie et al., 1986) and single radial immunodiffusion (SRID) assay (Mancini et al., 1965), respectively. The serum lysozyme and IgG concentrations in the unknown sera samples were then estimated using regression equation: where, Y, concentration of serum lysozyme/ IgG in unknown sera sample; b, slope of regression equation; c, intercept of regression equation; and x, diameter of the lysed/ precipitation zone around the unknown samples. Data on various layer economic traits such as age at first egg (AFE), egg weight (EW) at 28, 40and 64 weeks of age and egg production (EP) upto 40 and 64 weeks of age were recorded.
The influence of immunocompetence levels of layer on its economic performance traits were assessed by least squares analysis of variance (Harvey, 1990) taking immunocompetence levels as independent variable when HA titre, serum lysozyme and serum IgG concentrations were classified in high, medium and low levels based on their means and standard deviation. Critical difference (CD) test at 5% level of probability of significance was performed for assessing critical differences among the least squares means under individual immunocompetance levels.
Results and Discussion
The estimated least squares means of HA titre, serum lysozyme and serum IgG concentrations in the selected strain of RIR chicken were 9.33±0.34, 4.42±0.18 μg/ml and 8.72±0.41 μg/μl, respectively. Present finding are in accordance compared with the earlier reports of pure lines RIR chicken (Das et al., 2016; Rahim et al., 2015). Saini et al. (2008) estimated 4 dpi HA titre of 5.20 and 4.70 in RIR-C (CARI strain) and RIR-B (Bhubaneswar strain) chicken, respectively. Jaiswal et al. (2014) reported the corresponding estimates as 7.93±0.24, 07±0.29μg/ml and 12.15±0.48 mg/ml in Kadaknath chicken. However, Kokate et al. (2016) reported relatively higher estimates of HA titre (10.84±0.18, 21.28±0.78μg/ml and 24.23±2.05μg/μl), serum lysozyme (11.62±0.21, 16.91±0.93 μg/ml and 15.70±2.44 μg/μl) and serum IgG concentrations (11.94±0.15, 9.42±0.68 μg/ml and 10.27±1.79 μg/μl) in Aseel, Kadaknath and IWH line of White Leghorn chicken. Singh et al. (2010) studied higher serum IgG (10.61± 20.25mg/ml) and lower serum lysozyme (2.13 ± 0.03mg/ml) concentration in Aseel native chicken than the present findings in RIR chicken. The attributed variations might mainly be due to differences in genetic makeup of different stocks, routes of SRBC administration and other factors like differences in management condition and age of the birds at the time of estimation of traits.
Influence of IC Traits Levels on Layer Performance
The least squares means of different layer economic traits under different immunocompetence levels in the selected strain of RIR chicken were presented in Table 1. Analysis revealed that serum lysozyme levels had significant (P≤0.05) influence on egg production upto 64 weeks of age of the chicken. Pullets with high serum lysozyme level laid highest (P≤0.05) number of eggs upto 64 weeks of age followed by the pullets with medium serum lysozyme level and then the pullets with low levels (Table 1). Significant influence of birds’ immunocompetence levels on their layer performances observed in the present study was of interest and reports in this regard were limited. Although, few reports in this regard have recently appeared in literature. CARI Debendra chicken with medium or low serum lysozyme level was reported to have higher (P≤0.05) body weight at 40th week of age than those with high serum lysozyme level (Das et al., 2014a). Again, CARI-Sonali chicken with medium serum lysozyme level had lower (P≤0.05) age at first egg than those with high level of serum lysozyme level (Das et al., 2014b).
HA titre and serum IgG levels had non-significant influence on any of the layer economic traits in the selected strain of RIR chicken in present investigation. Van der Zijpp and Nieuwland (1986) reported higher egg number and egg weight for those birds containing high HA titre than low HA titre in ISA Warren chicken line. However, Das et al. (2014a) reported non-significant effect of HA titre and significant effect of serum IgG levels on few layer traits in CARI-Debendra pullets.
Table 1: Least squares means of different layer economic traits under different immunocompetence levels in the selected strain of RIR chicken
|Factor||Obs.||Least squares Means ± Standard error|
|AFE (nos.)||EW28 (g)||EW40 (g)||EW64 (g)||EP40 (nos.)||EP64 (nos.)|
|HA titre levels|
|Serum lysozyme levels|
|Serum IgG levels|
Means within a column under a factor having different superscripts differ significantly (P≤0.05).
The present investigation concluded that the high serum lysozyme level had significant association for part period egg production upto 64 weeks of age followed by medium and then low lysozyme level in the selected strain of RIR chicken. Present findings suggested that serum lysozyme could be utilized for improvement of both production traits as well as general immune responsiveness of birds after validation on large number of samples to accurately associate immunocompetence levels with layer performance traits.
Authors acknowledge the financial support from UGC, New Delhi in the form of Rajiv Gandhi National Fellowship to the first author and Directors of Central Avian Research Institute, Izatnagar for providing the necessary facilities for this investigation.