PhD

The study was conducted with the objective of ascertaining the efficacy of certain antistress agents as probiotic with multiple strains of bacteria and yeast (Protexin), antibiotic as virginiamycin (Stafac-20) and vitamin C in ameliorating the overcrowding stress induced during summer and rainy seasons in respect of physiological, biochemical, hormonal, immunological and production parameters of broiler chicken. The experiment was carried out on one-month-old Vencob broiler chicks in two separate phases; phase-I during summer and phase II during rainy season. In each seasonal phase, the birds were divided into five groups with 12 birds in each group. Each group was replicated twice. The birds in different groups were G-I – unstressed control birds (provided with a floor space of 696 cm2/bird), G-II – stressed control (floor space reduced by 50% to have a space allowance of 348 cm2/bird), G-III – overcrowded birds supplemented with Protexin at the rate of 0.025 per cent in the diet, G-IV- overcrowded birds supplemented with virginiamycin at the rate of 0.002 per cent in the diet, and G-V- overcrowded birds supplemented with vitamin C at the rate of 0.03 per cent in the diet.

Blood samples were collected from six birds in each replicate using appropriate anticoagulants. Haematological parameters were estimated using the whole blood. Plasma samples were separated and used for estimating biochemical and hormonal parameters. Quantification of immunoglobulin G (IgG) and electrophoretic separation of plasma proteins were carried out. Heterophil:Lymphocyte (H:L) ratio and lymphoblastogenic response were also recorded. The data were analysed statistically using appropriate tools.

Values of total erythrocyte count (TEC), concentration of haemoglobin (Hb), volume of packed red blood cells (VPRC), mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC), total leukocyte count (TLC) monocyte percentage, concentration of plasma total proteins, plasma alanine amino transferase (ALT) activity, plasma concentration of triiodothyronine (T3) and thyroxine (T4), organ weight of different organs as heart, spleen, liver, gizzard, fat percentage and dressing percentage were not significantly affected by applied stress of overcrowding. The percentage of heterophils, lymphocytes, basophils, H/L ratio, plasma concentration of globulin, total lipids, total cholesterol, and glucose, activities of plasma enzymes such as aspartate amino transferase (AST), lactate dehydrogenase (LDH), body weight, body weight gain, feed intake, and feed efficiency were influenced by overcrowding stress in both summer as well as rainy seasons. Although the concentration of stress hormones (cortisol and corticosterone) increased significantly (P0.05) by overcrowding stress in six week old broilers, continued application of the same stress caused waning off the increase to merely insignificant level. The applied stress and summer heat deteriorated the immune status of the broilers whereas the supplemented feed additives normalised many of the stress-induced changes in the haematological, biochemical and production parameters. Out of the antistress feed supplements used vitamin C was found more efficacious and economical than Protexin and virginiamycin in repealing the stress induced alterations in broilers at six and eight weeks of age both in summer and rainy seasons. Virginiamycin supplementation adversely affected the haematological parameters.

Seasons significantly changed the concentration of Hb, VPRC, heterophil count, lymphocyte count, H/L ratio, plasma LDH activity, plasma concentration of T3, T4, and cortisol as well as body weight of broiler chicken. The values of heterophil count, H/L ratio, plasma concentration of LDH, and cortisol were higher in summer, whereas, lower values were observed for Hb concentration, VPRC, lymphocyte count, plasma concentration of T3 and T4 and body weight. The birds in summer gave a better economical gain than those in rainy season. Haematological parameters such as TEC, TLC, MCH, percentages of monocytes, basophils, biochemical parameters such as plasma concentration of glucose, total proteins, albumin, globulin, A:G ratio, plasma concentration of total lipids, triglycerides, total cholesterol, AST, and ALT, corticosterone and production parameters such as body weight gain, organ weight, body fat percentage and dressing percentage were not significantly affected by seasons. Both overcrowding and summer heat stress reduced the feed intake of broilers.

The plasma concentration of albumin, total lipids, cholesterol, glucose, AST, ALT, and LDH were increased significantly with the increase in age (4-8 weeks period) in both seasons. Significant reductions in the plasma concentration of corticosterone and T3 were noticed with the advancement of age. The values of VPRC, TLC, plasma concentration of globulin, A:G ratio, plasma concentration of triglycerides and cortisol, were not significantly affected by the age of the birds (4 to 8 weeks).

From the results of the study it could be inferred that stress of overcrowding adversely affected many of the physiological, biochemical and production parameters of six and eight week old broiler chicken. Antistress feed supplements such as Protexin, virginiamycin and vitamin C were effective to rectify most of the stress-associated changes, but not all. The vitamin C was found better and more economical than other feed additives as Protexin and virginiamycin. Dietary supplementations of antistress agents were more effective in overcrowded, heat stressed birds of summer season than their counter parts of rainy season.