Effects Of Exposure To Humidity And Ammonia-induced Chronic Stress On Growth Performance, Meat Quality, Physiological Function In Broilers And Its Regulating Mechanism

The aim of this research was to determine the effect of ammonia concentration andrelative humidity in poultry house on growth performance, meat quality and immunologicalfunction in broilers, as well as primarily probe into the regulating mechanism of whichchanges in performance of birds are resulted by exposure to humidity and ammonia-inducedchronic stress. A total of288twenty one-day-old male broiler chicks were randomly dividedinto6groups, each group had six replicates, and each replicate contained8birds. These birdswere randomly assigned to6climate chambers in a2×3factorial arrangement with twoammonia concentration (30mg/kg or70mg/kg) and three relative humidity levels(35%,60%,85%), respectively, from21to42d of age. The growth performance (feed intake, daily gain,feed/gain), carcass quality(carcass ratio, percentage of pectoralis, percentage of thigh muscle,percentage of abdominal fat), meat quality (meat color, drip loss, shear force and pH),development of major tissue (heart, liver and immune organ), morphology of tissue (trachea,lung, immune organ and small intestine), as well as antioxidant property (SOD, T-AOC,GSH-Px and TBARS), blood biochemical parameter (blood ammonia, blood glucose,corticosterione, xylose, enzyme in blood, and so on), immunoreactions (nonspecific index andspecific index, cytokine,) and gene (NF-κB, IL-1, IL-6, IL-4, IL-10) expression were tested.The main results of this study were showed as follows:1The effect of ammonia and humidity on growth performance, carcass yield, antioxidantproperty and meat qualityThe results showed that comparing with30mg/kg ammonia exposure,70mg/kg ammoniaexposure decreased AFI and G (P<0.05), GSH-Px concentration (P<0.01), a*value45min afterslaughtering (P<0.01) of breast of broiler and increased carcass ratio (P<0.01), TBARS levelfive and seven days after slaughtering (P<0.05), dropping loss (P<0.01), shear force (P<0.05),L*value (P<0.05) and b*value (P<0.01)45min after slaughtering of breast of broiler.The birds exposed to85%RH had lower G (P<0.01), feed ratio (P<0.05), carcass ratio(P<0.05), b*value (P<0.01) of breast45min after slaughtering, and higher L*value of breast(P<0.01)45min after slaughtering than those exposed to60%, respectively. Moreover, thebirds exposed to35%or85%RH had lower GSH-Px concentration in breast (P<0.01), andhigher TBARS level in breast five and seven days after slaughtering (P<0.05) than those exposed to60%, respectively.Birds in70mg/kg ammonia+35%RH and70mg/kg ammonia+85%RH had lower a*value of breast45min after slaughtering than those in30mg/kg ammonia+60%RH(P<0.05).2The effect of ammonia and humidity on the development and morphology of selectedorgans and the intestinal contentsAmmonia exposure had effect on respiratory system and lung of broiler.70mg/kgammonia exposure atrophy and degenerate tracheal epithelial, increased the secretion ofmucus, lead to pulmonary congestion and bleeding point.35%RH treatment aggravate thedamage of respiratory system by70mg/kg ammonia. Ammonia and humidity chronic stressalso atrophy the immunological tissue, in which,70mg/kg ammonia+35%RH was the mostseriously influence factors on the harderian gland. Comparing with30mg/kg ammoniaexposure,70mg/kg ammonia exposure decreased small intestinal villus height (VH) and cryptdepth (CD)(P<0.05), and increased pH of duodenal (P<0.01) and jejuna (P<0.05) contents,total volatile basic nitrogen concentration in ileum (P<0.01) of broiler.Birds exposed to85%RH had lower small intestinal VH and CD (P<0.05), and higherpH of ileunal contents (P<0.05) than those exposed to60%RH. The small intestinal VH andCD of birds exposed to35%RH also had a declined trend, especially duodenal CD andjejunal VH and CD，which decreased significantly than those exposed to60%RH (P<0.05),respectively.3The effect of ammonia and humidity on selected blood physiological and biochemicalparametersComparing with30mg/kg ammonia exposure,70mg/kg ammonia exposure increasedblood ammonia level (P<0.01), red blood cell, hemoglobin, packed-cell volume (PCV), meancorpuscular volume (MCV)(P<0.05), uric acid, blood urea nitrogen (BUN)(P<0.01), theactivity of lactate dehydrogenase, alkaline phosphatase (ALP), aspartate aminotransferase(AST)(P<0.01) in blood; but declined the activity of superoxide dismutase(SOD), totalantioxidant capacity (T-AOC), glutathione peroxidase (GSH-Px)(P<0.01) and xylose in blood(P<0.05). Birds exposed to70mg/kg ammonia had higher blood glucose in the first andsecond week (P<0.05) and had lower blood glucose in the third week (P=0.072) than thoseexposed to30mg/kg ammonia.70mg/kg ammonia exposure also increased bloodcorticosterone of broiler in the first week (P=0.051).The birds exposed to85%RH had higher red blood cell, hemoglobin, PCV, MCV(P<0.05), blood urea nitrogen (P<0.01), the activity of lactate dehydrogenase, ALP, AST(P<0.01) in blood and had lower activity of T-AOC, GSH-Px (P<0.05) than those exposed to60%RH. The birds exposed to35%RH also had higher red blood cell, PCV, MCV (P<0.05)a n d a c t i v i t y o f A S T (P <0.01) t h a n t h o s e e x p o s e d t o60%R H.Bird in70mg/kg ammonia+85%RH had higher blood ammonia level (P<0.01), BUN (P<0.01) and AST activity (P<0.05) in blood in the third week than those in30mg/kgammonia+60%RH.4The effect of ammonia and humidity on immune function and related gene expressionof broilersThe results showed that ammonia concentration in poultry house affected the immunefunction of broiler. Comparing with30mg/kg ammonia exposure,70mg/kg ammoniaexposure decreased globulin concentration in the third week (P<0.01), lysozymeconcentration in the second week (P<0.01), Newcastle disease virus antibody titers(P<0.05),lymphocyte stimulus index (P<0.05) in blood and SIgA content in duodenum andtrachea(P<0.05), but increased the concentration of IL-1β, IL-4, IL-10(P<0.05) in blood andthe expression of NF-B1，IL-1β，IL-6，IL-4, IL-10mRNA (P<0.01) in speen of broiler,respectively.Relative humidity also affected the immune function of broiler. Comparing with60%RH,85%RH declined thymus index (P<0.05), lysozyme concentration in blood (P<0.01) andSIgA content in duodenum and trachea (P<0.05), but increased the concentration of IL-1β，IL-10(P<0.01) in blood and the expression of NF-B1, IL-1β, IL-6, IL-4, IL-10mRNA(P<0.05) in speen of broiler, respectively. Comparing with60%RH,35%RH also increasedthe expression of IL-1β，IL-6mRNA (P<0.05). There was insignificant difference of thymusindex, lysozyme concentration in blood, SIgA content in duodenum and trachea and theexpression of NF-B1, IL-4, IL-10mRNA between60%RH and35%RH(P>0.05).Birds exposed to70mg/kg ammonia+85%RH had higher NF-B, IL-1β, IL-6mRNAexpression in speen, blood IL-1β concentration in the third week, IL-6concentration in thesecond week and lower immune organ index in the third week, total serum protein andgglobulin, ConA stimulating index, SIgA concent in trachea and small intestine than those in30mg/kg ammonia+60%RH (P<0.05), respectively.These results of present research revealed that humidity and ammonia-induced chronicstress could cause oxidative stress, immunological stress, and damage some importantfunctional organs or tissues etc., as well as cause a series of the defensive physiologicalresponses of broilers, such consequences could lead to comprehensive decline inphysiological function, finally resulting in significantly reduce in growth performance andmeat quality of broilers.