Single or Combined effect of zinc and probiotics on gut morphology, muscle and hematological parameters of healthy and heat stressed broiler chicken

Abstract

Heat stress is a major problem of the tropical countries including Pakistan. It has negative impact on poultry production and causes high economic losses. It has negative impact on growth performance, gastrointestinal morphology, meat quality and alters serum biochemistry of broiler chicken. Zinc and probiotics have a role in amelioration of negative effects of stress. The current study aimed to determine the effect of zinc and probiotics either individually or in combination on the growth performance, gut histomorphology, meat quality and serum biochemical parameters in normal and heat-stressed broiler chicken. The study comprised of two trials and the trials were performed at broiler experimental house (Ravi campus), University of Veterinary and Animal Sciences Lahore, Pakistan. Experiment I was performed on day-old 192 broiler chicks for six weeks (42 days) under normal environmental conditions. The chicks were divided into six treatment groups including Control (basal diet), Zn30 (Basal diet+30mg ZnSO4.H2O/kg feed), Zn60 (Basal diet+60mg ZnSO4.H2O/kg diet), Pro (Protexin® 0.1g/kg diet),Com30 (Basal diet+30mg ZnSO4.H2O/kg feed+Protexin® 0.1g/kg diet) and Com60 (Basal diet+60mg ZnSO4.H2O/kg feed+Protexin® 0.1g/kg diet). Each treatment comprised of four replicates (8 birds per replicate).Two types of feed were adopted i.e. starter (0-21 days) and grower (22-42 days). At day 42 two birds from each replicate (8 birds/ group) were slaughtered and the parameters for growth performance (body weight, feed intake, body weight gain, feed conversion ratio), intestine (villus height, Crypt depth, villus height: crypt depth ratio, villus surface area, goblet cell count and intraepithelial count in duodenum, jejunum and ileum), ceacal tonsil (length, width, area of lymphatic nodule), bursa of Fabricius (length, width, area of lymphoid follicle), meat quality (pHi, pHu, drip loss, muscle fiber diameter and cross sectional area, muscle fascicle diameter and its cross sectional area) were measured. The result showed that zinc supplementation improved the performance parameters including body weight and feed intake. It also increased villus height in duodenum, goblet cell count and intraepithelial count in ileum. The drip loss decreased and muscle fiber diameter, muscle fascicle diameter increased in zinc supplemented groups. Zinc supplementation also elevated the serum cholesterol and zinc levels. The probiotic supplementation either individually or in combination with zinc improved weight gain, feed efficiency, increased villus height: crypt depth ratio in duodenum, goblet cell and intraepithelial lymphocyte count in ileum when compared to control group. The probiotics singly or in combination with zinc improved meat quality through increase in ultimate pH, muscle fiber and muscle fascicle diameter and decrease in drip loss. The serum cholesterol decreased with probiotic supplementation. Experiment II was carried on 280 day-old chicks that were randomly divided in seven treatment groups i.e. Control (basal diet), HS (basal diet), HS-Zn30 (Basal diet+30mg ZnSO4.H2O/kg feed), HS-Zn60 (Basal diet+60mg ZnSO4.H2O/kg diet), HS-Pro (Protexin® 0.1g/kg diet), HS-Com30 (Basal diet+30mg ZnSO4.H2O/kg feed+Protexin® 0.1g/kg diet) and HS-Com60 (Basal diet+60mg ZnSO4.H2O/kg feed+Protexin® 0.1g/kg diet). Each group was comprised of five replicates (8 birds/group). The control group was kept under normal environmental temperature. Rest of the groups were exposed to cyclic heat stress from 22nd day onwards. The heat-stressed birds were kept at high ambient temperature (35±1˚C) and relative humidity (75±5%) for 8 hours (9:00am to 5:00 pm) followed by normal environmental temperature (26˚C) and relative humidity (65±5 %). The experiment duration and diet protocol was same as adopted in experiment I. On day 42, two birds from each replicate (10 birds/ group) were slaughtered. The parameters measured were same as in experiment I. The results presented that heat stress adversely influenced the performance parameters (feed intake, weight gain, feed conversion ratio), intestinal parameters (villus height, villus height: crypt depth ratio, villus surface area, goblet cell and intraepithelial count), meat quality (pHi, pHu, muscle fiber diameters and cross sectional area) and serum biochemical parameters (cortisol, cholesterol and zinc). The dietary addition of zinc and probiotic alone or in combination improved the relative weight of spleen, pancreas, and bursa of Fabricius. The area of lymphatic nodule and lymphoid follicles was higher with combined supplementation of zinc and Probiotic. Single or combined supplementation of zinc and probiotic increased villus surface area, total goblet cell count in all segments of intestine and intraepithelial lymphocytes in jejunum and ileum. The results of the present experiment revealed that single or combined dietary supplementation of zinc and probiotic have positive impact on growth performance, intestinal histomorphology, meat quality and serum biochemical parameters in broiler chicken reared under cyclic heat stress.