Poultry industry has undergone substantial expansion during last few decades. Tremendous development in the fields of genetics, nutrition and management has helped the producer to maximize the feed efficiency, and in turn, the economic gains. Nevertheless, with an increase in performance, sensitivity of the bird also increased tremendously particularly towards the thermal stressors. Therefore, the nutrition and health care of the poultry, particularly broiler, became more demanding. In order to promote the gut or general health of broiler during the heat or cold exposure, antibiotic growth promoters (AGPs) were routinely practiced. Their usefulness in the poultry practice was seldom questioned but the development of antibiotic-resistant superbugs and antibiotic residues in the meat prompted a serious public concern leading to ban on AGPs in animal diet by the European Commission in 2006. Exclusion of AGPs from the diet led to serious health problems in broiler and within two years of this ban the consumption of therapeutic antibiotic reached the same level as that of the AGPs before ban. Therefore, it was realized that simple ban on the AGPs will not resolve this issues unless new feeding and managemental strategies are devised to maintain or raise the performance of broiler. As an alternative to AGPs many agents have been experimentally evaluated in poultry and livestock like prebiotics, probiotics and organic acids. Use of prebiotics in poultry showed variable degree of success with considerable data suggesting their positive influence during stressful situations like crowding, poor management and temperature extremes etc. which are invariably a part and parcel of commercial broiler production. Keeping in view the importance of seeking AGP alternatives, current study was planned to evaluate the effects of novel β- galacto-oligosaccharides (β-GOS) on various histo-physiological parameters of thermally-stressed broiler.
Summary
145
In experiment I, 125 day-old broilers were randomly divided into five treatment groups (N=25) with five replicates (n=5) in each group. Till d-21, all the groups were raised under standard management. From d-22, four groups received cyclic heat stress (35°C for 8hrs/day) and control (TNZ) group received 26.7°C till 35th day. TNZ and heat-stressed (HSCT) group received corn-based basal diet (CBBD) whereas three remaining groups i.e. HS+0.1%β-GOS, HS+0.2%β-GOS and HS+0.5%β-GOS received CBBD supplemented with 0.1%, 0.2% and 0.5% β-GOS respectively for 35 days. All groups received primary and booster vaccines against Newcastle Disease Virus (NDV) and Infectious Bursal Disease Virus (IBDV). The zootechnichal parameters included daily feed consumption (FC), body weight (BW) and feed efficiency (FE). Later two parameters were calculated on weekly basis. At the end of trial, 10 birds per group i.e. 2/replicate were killed to collect blood, viscera, small intestine, bursa and cecal tonsils for determination of serum hormones, relative weights of viscera (RWO) and histomorphometry, respectively. Data were analyzed using one way analysis of variance (ANOVA) and subjected to post hoc Duncan’s multiple range (DMR) test (P < 0.05). Exposure to the HS reduced (P < 0.05) all the zootechnichal parameters, RW of liver, bursa of Fabricius and small intestine, serum triiodothyronine (T3), thyroxine (T4), villus surface area (VSA), height (VH), width (VW), crypt depth (CD) and intraepithelial lymphocyte count (IELs) in small intestine compared to TNZ group. The serum cortisol and count of acidic mucin containing goblet cells (AGCs) increased (P < 0.05) in jejunum while they decreased (P < 0.05) in ileum of HSCT group compared with TNZ. Improvement (P< 0.05) in the FE of the 0.5% β-GOS supplemented heat-stressed birds was comparable to TNZ group. Furthermore, supplementation of 0.5% β-GOS improved (P< 0.05) serum T3 and T4 and 0.2% β-GOS reduced (P< 0.05) serum cortisol without achieving their pre-HS levels. All the dietary inclusions of β-GOS improved (P< 0.05) histomorphometry
Summary
146
of small intestine including VH, CD and VSA compared to HSCT group. The 0.5% β-GOS improved (P< 0.05) these parameters beyond TNZ. Intestinal IEL count improved (P< 0.05) with 0.1% β-GOS supplementation without achieving the pre-HS levels. Count of jejunal and ileal AGCs reduced (P< 0.05) with 0.2 and 0.5% β-GOS supplementation compared with HSCT. Neither HS nor supplementation affected the morphometry of the bursa of Fabricius and cecal tonsils.
In experiment II, 125 day-old broilers were randomly divided into five treatment groups (N=25) with five replicates (n=5) in each group. Till d-21, all the groups were raised under standard management. From d-22, four groups received cyclic cold stress (15°C±2°C for 8hrs/day) and control (TNZ) group received 26.7°C till 35th day. TNZ and cold-stressed (COLD) group received corn-based basal diet (CBBD) whereas three remaining groups CS+0.1%β-GOS, CS+0.2%β-GOS and CS+0.5%β-GOS received CBBD supplemented with 0.1%, 0.2% and 0.5% β-GOS, respectively for 35 days. All groups received primary and booster vaccines against NDV and IBDV. The zootechnichal parameters included daily FC, BW and FE. Later two parameters were calculated on weekly basis. At the end of trial, 10 birds per group (2/replicate) were killed to collect blood, viscera, small intestine, bursa and cecal tonsils for determination of serum hormones, RWO and histomorphometry, respectively. Data were analyzed using ANOVA and subjected to DMR test (P<0.05). Exposure to cold stress increased (P<0.05) the FC, serum T3 and cortisol and reduced (P<0.05) BW and performance compared with TNZ group. Moreover, COLD group was also presented with increased (P<0.05) RW of liver and heart, decreased (P<0.05) RW of ceca compared with TNZ group. The VSA of small intestine and IEL count in duodenum and jejunum reduced (P<0.05), whereas, AGCs count increased (P<0.05) due to the exposure to cold stress. The RWs of immune organs and their histomorphometry was not
Summary
147
affected during cold stress when compared with TNZ group. Dietary inclusion of 0.5% β-GOS achieved the pre-cold stress levels of FCR. Supplementation of 0.2% and 0.5% β-GOS reversed (P< 0.05) the hormonal changes of cortisol and T3, respectively when compared with COLD group. All the dietary inclusions of β-GOS improved (P<0.05) morphometric parameters in duodenum. The 0.5% β-GOS-induced-improvement (P<0.05) in these parameters was beyond the values observed for TNZ group. In ileum, 0.2% β-GOS supplementation resulted in most distinct (P<0.05) increase of VH, VW and VSA which was comparable to that observed for TNZ group. The jejunal morphometric parameters also improved (P<0.05) with the β-GOS supplementation, but the pre-cold stress values were not attained. The IEL count increased (P<0.05) in the duodenum and decreased (P<0.05) in the jejunum and ileum of all the β-GOS supplemented groups. The AGCs count increased (P<0.05) in duodenum and jejunum of 0.1% and 0.2% β-GOS-supplemented groups whereas the count of AGCs in ileum remained unaffected in all the β-GOS supplemented groups compared to the TNZ group. Morphometry of the bursa or cecal tonsils was not influenced by the supplementation of β-GOS.
In conclusion, dietary supplementation of 0.5% β-GOS helped to improve the growth performance in thermally-stressed broilers owing to its positive influence on intestinal morphometry and the dynamics of cortisol and thyroid hormones.