Selenium exerts protective effects against heat stress-induced barrier disruption and inflammation response in jejunum of growing pigs.

BACKGROUND: Heat stress (HS) has a negative impact on the intestinal barrier and immune function of pigs. Selenium (Se) may improve intestinal health through affecting selenoproteins. Thus we investigate the protective effect of new organic Se (2-hydroxy-4-methylselenobutanoic acid, HMSeBA) on jejunal damage in growing pigs upon HS and integrate potential roles of corresponding selenoproteins. RESULTS: HS decreased the villus height and increased (P < 0.05) the protein abundance of HSP70, and downregulated (P < 0.05) protein levels of tight junction-related proteins (CLDN-1 and OCLD). HS-induced jejunal damage was associated with the upregulation of four inflammation-related genes and ten selenoprotein-encoding genes, downregulation (P < 0.05) of four selenoprotein-encoding genes and decreased (P < 0.05) the protein abundance of GPX4 and SELENOS. Compared with the HS group, HMSeBA supplementation not only elevated the villus height and the ratio of V/C (P < 0:05), but also reduced (P < 0.05) the protein abundance of HSP70 and MDA content, and increased (P < 0.05) the protein abundance of OCLD. HMSeBA supplementation downregulated the expression of seven inflammation-related genes, changed the expression of 12 selenoprotein-encoding genes in jejunum mucosa affected by HS, and increased the protein abundance of GPX4, TXNRD1 and SELENOS. CONCLUSION: Organic Se supplementation beyond nutritional requirement alleviates the negative effect of HS on the jejunum of growing pigs, and its protective effect is related to the response of corresponding selenoproteins. © 2021 Society of Chemical Industry.

Stress and immunity in poultry: light management and nanotechnology as effective immune enhancers to fight stress.

The poultry industry plays a significant role in boosting the economy of several countries, particularly developing countries, and acts as a good, cheap, and affordable source of animal protein. A stress-free environment is the main target in poultry production. There are several stressors, such as cold stress, heat stress, high stocking density, and diseases that can affect birds and cause several deleterious changes. Stress reduces feed intake and growth, as well as impairs immune response and function, resulting in high disease susceptibility. These effects are correlated with higher corticosteroid levels that modulate several immune pathways such as cytokine-cytokine receptor interaction and Toll-like receptor signaling along with induction of excessive production of reactive oxygen species (ROS) and thus oxidative stress. Several approaches have been considered to boost bird immunity to overcome stress-associated effects. Of these, dietary supplementation of certain nutrients and management modifications, such as light management, are commonly considered. Dietary supplementations improve bird immunity by improving the development of lymphoid tissues and triggering beneficial immune modulators and responses. Since nano-minerals have higher bioavailability compared to inorganic or organic forms, they are highly recommended to be included in the bird's diet during stress. Additionally, light management is considered a cheap and safe approach to control stress. Changing light from continuous to intermittent and using monochromatic light instead of the normal light improve bird performance and health. Such changes in light management are associated with a reduction of ROS production and increased antioxidant production. In this review, we discuss the impact of stress on the immune system of birds and the transcriptome of oxidative stress and immune-related genes, in addition, how nano-minerals supplementations and light system modulate or mitigate stress-associated effects.

Dietary curcumin supplementation effects on blood immunological profile and liver enzymatic activity of laying hens after exposure to high temperature conditions.

Various environmental factors affect livestock production but heat stress is a major challenge in the poultry farming. Poultry exposes to high temperature alters blood immunological parameters and liver enzymatic function which in turn, suppress the immunity and disease resistance of chickens. Thus, the purpose of present study was to explore the effect of dietary curcumin supplementation on blood immunological biomarker and liver enzymatic activity of laying hens under heat stress conditions. Experimental groups contained two control groups (normal temperature control (NC) and heat stress control (HC) and 3 heat stress curcumin treatment groups (HT100, HT200 and HT300). Hens in HC group with basal diet and heat stress curcumin treatment groups were exposed 6 h/day heat stress (32 ± 1 °C) from 10:00 a.m. to 16:00 p.m. for 9 week. The results of present study showed that heat stressed curcumin treatment group had improved liver weight, WBC values and immunoglobulin level as compared to untreated HC and NC groups. The available results also indicated that laying hens supplemented with curcumin under high temperature conditions had reduced H/L ratio, serum corticosterone levels, inflammatory cytokines response and liver enzymatic activity (ALT) which enhanced the immunity of laying hens under hot climatic conditions. Therefore, it is concluded that curcumin has ability to combat harsh environmental conditions which can be used as anti-inflammatory and immune booster feed additive in the poultry nutrition.

Effect of curcumin supplementation on TLR4 mediated non-specific immune responses in liver of laying hens under high-temperature conditions.

The liver performs a significant role in innate and adaptive immunity. Heat stress causes oxidative stress in liver tissues and reduces the immune responses of laying hens which can cause several diseases affecting poultry-production performance. Hepatic inflammation is a common trigger of liver disease, which is reflected by hepatic tissue damage leading to fibrogenesis and hepatocellular carcinoma. Dietary manipulation of curcumin has been proposed to ameliorate the immune status of chickens under heat stress. Thus, this study aimed to investigate the effect of curcumin supplementation on TLR4 mediated non-specific immune response in liver of laying hens under high-temperature conditions. Experimental groups contained two controls groups (high temperature and thermo-neutral control (HC and NC) fed basal diet) and three high-temperature curcumin treatments groups (HT100, HT200 and HT300). Laying hens in HC and HT groups exposed 6 h/day heat stress (32 ±â€¯1 °C). The results of present study showed that heat stress curcumin treatment group had reduced inflammatory responses (IL-6, IL-1ß, TNF-α) as compared to HC and NC group. Pathological lesions and DNA damage of immune tissues were decreased in heat stress curcumin supplementation as compared to HC and NC group. Furthermore, PCNA, TLR4 and its downstream gene expression as well as protein expression (TLR4, NF-κB and PCNA) were significantly down regulated in heat stress curcumin supplemented group as compared to HC and NC group. Therefore, it is concluded that heat stressed hens supplemented with dietary curcumin enhance the immunity of laying hens and combat stressful environmental conditions.

Effects of early feeding and dietary interventions on development of lymphoid organs and immune competence in neonatal chickens: A review.

With the ongoing intensification of the poultry industry and the continuous need to control pathogens, there is a critical need to extend our understanding of the avian immune system and the role of nutritional interventions on development of immune competence in neonatal chicks. In this review, we will focus on the ontogeny of the lymphoid organs during embryonic life and the first 2 weeks post-hatch, and how early feeding practices improve heath and modulate the development and function of the immune system in young chicks. The evidence for the positive impact of the nutrition of breeder hens on embryonic development and on the survival and immunity of their chicks will also be outlined. Additionally, we will discuss the vital role of supplemental feeding either in ovo or immediately post-hatch in chick health and immunity and the importance of these approaches in ameliorating immune system functions of heat-stressed chicks. To conclude, we provide some perspectives on a number of key issues, concerning the mechanisms of nutritional modulation of immunity, that need to be addressed. A thorough investigation of these mechanisms may assist in the formulation of diets to improve the immunity and general health status.

Effects of feeding an immunomodulatory supplement to heat-stressed or actively cooled cows during late gestation on postnatal immunity, health, and growth of calves.

Heat stress during late gestation negatively affects the physiology, health, and productivity of dairy cows as well as the calves developing in utero. Providing cows with active cooling devices, such as fans and soakers, and supplementing cows with an immunomodulating feed additive, OmniGen-AF (OG; Phibro Animal Health Corporation), improves immune function and milk yield of cows. It is unknown if maternal supplementation of OG combined with active cooling during late gestation might benefit the developing calf as well. Herein we evaluated markers of innate immune function, including immune cell counts, acute phase proteins, and neutrophil function, of calves born to multiparous dams in a 2 × 2 factorial design. Dams were supplemented with OG or a bentonite control (NO) beginning at 60 d before dry off and exposed to heat stress with cooling (CL) or without active cooling (HT) during the dry period (∼46 d). At birth, calves were separated from their dams and fed 6.6 L of their dams' colostrum in 2 meals. Calf body weight and rectal temperature were recorded, and blood samples were collected at birth (before colostrum feeding) and at 10, 28, and 49 d of age. Calves born to either CL dams or OG dams were heavier at birth than calves born to HT or NO dams, respectively. Concentrations of serum amyloid A were higher in the blood of calves born to OG dams relative to NO and for HT calves relative to CL calves. In addition, calves born to cooled OG dams had greater concentrations of plasma haptoglobin than calves born to cooled control dams. Neutrophil function at 10 d of age was enhanced in calves born to cooled OG dams and lymphocyte counts were higher in calves born to OG dams. Together these results suggest that adding OG to maternal feed in combination with active cooling of cows during late gestation is effective in mitigating the negative effects of in utero heat stress on postnatal calf growth and immune competence.

Supplementing an immunomodulatory feed ingredient to modulate thermoregulation, physiologic, and production responses in lactating dairy cows under heat stress conditions.

This study compared vaginal temperature, physiologic, and productive parameters in lactating dairy cows supplemented or not with Omnigen-AF (Phibro Animal Health, Teaneck, NJ) during the summer months in a tropical environment. Thirty-two lactating, primiparous (n = 16) and multiparous (n = 16) pregnant Holstein × Gir cows were ranked by parity, days in milk, body weight, and body condition score (BCS), and assigned to receive (SUPP; n = 16) or not (CON; n = 16) Omnigen-AF (Phibro Animal Health, Teaneck, NJ) at 56 g/cow daily (as-fed basis). During the experimental period (d -6 to 56), cows were maintained in a single drylot pen with ad libitum access to water and a total mixed ration, and milked twice daily. Cows received Omnigen-AF mixed with 200 g of corn (as-fed basis) after the daily morning milking through self-locking head gates, whereas CON cows concurrently received 56 g of kaolin mixed with 200 g of corn. For feed intake evaluation, cows from both treatments were randomly divided in 4 groups of 8 cows each, and allocated to 8 individual feeding stations for 3 d. Intake was evaluated 4 times per group from d 1 to 56. From d -6 to 0, d 15 to 28, and d 43 to 56, cow vaginal temperature was recorded hourly. Environmental temperature-humidity index (THI) was also recorded hourly from d 15 to 28 and d 43 to 56. Cows were evaluated for body weight and BCS on d -6 and 56, individual milk production was recorded daily from d -6 to 56, and milk samples were collected on d -6, 0, 7, 14, 21, 28, 35, 42, 49, and 56 for analyses of somatic cell count and milk components. Blood samples were collected on d -6, -3, 0, 9, 15, 18, 21, 24, 27, 36, 45, 48, 51, 54, and 56. Results from samples or observations collected from d -6 to 0 were included as an independent covariate in each respective analysis. Environmental THI was 74.2 ± 0.5 and cows were exposed to THI >68 for 633 h within a total of 672 h of evaluation. Cows assigned to CON had greater vaginal temperature on d 28, 43, 45, and from d 48 to 55 (by 0.38 to 0.52%), as well as greater mean somatic cell count (by 97%) and serum haptoglobin concentrations (by 89%) compared with SUPP cows. Cows assigned to SUPP had greater mean dry matter intake (by 7%), BCS on d 56 (by 11%), and mean serum insulin concentrations (by 35%) compared with CON cows. Hence, SUPP ameliorated hyperthermia, improved nutritional status, and modulated systemic and mammary gland immune parameters in lactating dairy cows exposed to heat stress conditions.

Feeding rumen-protected gamma-aminobutyric acid enhances the immune response and antioxidant status of heat-stressed lactating dairy cows.

This experiment was conducted to investigate the effects of rumen-protected gamma-aminobutyric acid (GABA) on immune function and antioxidant status in heat-stressed dairy cows. Sixty Holstein dairy cows were randomly assigned to 1 of 4 treatments according to a completely randomized block design. The treatments consisted of 0 (control), 40, 80, or 120mg of GABA/kg DM from rumen-protected GABA. The trial lasted 10 weeks. The average temperature-humidity indices at 0700, 1400 and 2200h were 78.4, 80.2 and 78.7, respectively. Rectal temperatures decreased linearly at 0700, 1400, and 2200h with increasing GABA. As the GABA increased, the immunoglobulin (Ig) A and IgG contents and the proportions of CD4(+) and CD8(+) T lymphocytes increased linearly (P<0.05), whereas concentrations of interleukin (IL)-2, IL-4, IL-6 and tumor necrosis factor-α (TNF-α) decreased linearly (P<0.05). The activities of superoxide dismutase (SOD), glutathione-peroxidase (GSH-PX) and total antioxidant capacity (T-AOC) increased linearly (P<0.05), whereas malondialdehyde (MDA) content decreased linearly (P<0.05) with increasing GABA. These results indicate that rumen-protected GABA supplementation to heat-stressed dairy cows can improve their immune function and antioxidant activity.

Acute brief heat stress in late gestation alters neonatal calf innate immune functions.

Heat stress, as one of the environmental stressors affecting the dairy industry, compromises the cow milk production, immune function, and reproductive system. However, few studies have looked at how prenatal heat stress (HS) affects the offspring. The objective of this study was to evaluate the effect of HS during late gestation on calf immunity. Calves were born to cows exposed to evaporative cooling (CT) or HS (cyclic 23-35°C) for 1 wk at 3 wk before calving. Both bull and heifer calves (CT, n=10; HS, n=10) were housed in similar environmental temperatures after birth. Both CT and HS calves received 3.78 L of pooled colostrum within 12 h after birth and were fed the same diet throughout the study. In addition to tumor necrosis factor α, IL-1ß, IL-1 receptor antagonist (IL-1RA), and toll-like receptor (TLR)2, and TLR4 mRNA expression, the expression of CD14(+) and CD18(+) cells, and DEC205(+) dendritic cells were determined in whole blood samples at d 0, 3, 7, 14, 21, and 28. The neutrophil to lymphocyte ratio, differential cell counts, and the hematocrit were also determined. During late gestation, the HS cows had greater respiration rates, rectal temperatures, and tended to spend more time standing compared with the CT cows. The HS calves had less expression of tumor necrosis factor-α and TLR2 and greater levels of IL-1ß, IL-1RA, and TLR4 compared with CT calves. The HS calves also had a greater percentage of CD18(+) cells compared with the CT calves. Additionally, a greater percentage of neutrophils and lesser percentage of lymphocytes were in the HS calves compared with the CT calves. The results indicate that biomarkers of calves' immunity are affected in the first several weeks after birth by HS in the dam during late gestation.

Selenium and Polysaccharides of Atractylodes macrocephala Koidz Play Different Roles in Improving the Immune Response Induced by Heat Stress in Chickens.

The aim of the present study was to investigate the effect of acute heat stress (HS) on the chicken immune response and to examine the role of selenium (Se) and the polysaccharides of Atractylodes macrocephala Koidz (PAMK) in immune regulation in the chicken immune system. Two hundred chickens were randomly divided into two groups: the HS group and the control (Con) group. These chickens were treated with Se (0.3 mg/kg), PAMK (200 mg/kg) alone, and a combination of Se (0.3 mg/kg) and PAMK (200 mg/kg). The cytokines; antioxidative enzymes; and HSP60, HSP70, and HSP90 levels were examined in chicken immune organs. The results indicated that HS-induced immune dysfunction included increased levels of TNF-α, IFN-γ, IL-2, IL-4, HSP60, HSP70, HSP90, and malondialdehyde (MDA) as well as decreased levels of glutathione peroxidase (GPx) and superoxide dismutase (SOD) in immune organs (P < 0.05). Among the affected organs, the bursa of Fabricius was one primary target of HS. The immune dysfunction induced by HS was alleviated (P < 0.05 or not) by treatment with Se and PAMK in different immune organs. However, Se only regulated the expression of TNF-α and IFN-γ, and PAMK influenced more cytokines in immune organs. The results showed that Se specifically regulated the TNF-α and IFN-γ pathways. Therefore, Se and PAMK played different roles in improving the immune response in HS chicken.

Effect of heat stress during late gestation on immune function and growth performance of calves: isolation of altered colostral and calf factors.

Calves born to cows exposed to heat stress during the dry period and fed their dams' colostrum have compromised passive and cell-mediated immunity compared with calves born to cows cooled during heat stress. However, it is unknown if this compromised immune response is caused by calf or colostrum intrinsic factors. Two studies were designed to elucidate the effects of colostrum from those innate to the calf. The objective of the first study was to evaluate the effect of maternal heat stress during the dry period on calf-specific factors related to immune response and growth performance. Cows were dried off 46 d before expected calving and randomly assigned to 1 of 2 treatments: heat stress (HT; n=18) or cooling (CL; n=18). Cows of the CL group were housed with sprinklers, fans and shade, whereas cows of HT group had only shade. After calving, the cows were milked and their colostrum was frozen for the subsequent study. Colostrum from cows exposed to a thermoneutral environment during the dry period was pooled and stored frozen (-20 °C). Within 4h of birth, 3.8L of the pooled colostrum from thermoneutral cows was fed to calves born to both HT and CL cows. Day of birth was considered study d 0. All calves were exposed to the same management and weaned at d 49. Blood samples were collected before colostrum feeding, 24h after birth and twice weekly up to d 28. Total serum IgG concentrations were determined. Body weight was recorded at birth and at d 15, 30, 45, and 60. Relative to CL calves, HT calves were lighter at birth (38.3 vs. 43.1 kg), but no difference in weight gain was observed at d 60. Additionally, HT calves had lower apparent efficiency of IgG absorption (26.0 vs. 30.2%), but no differences were observed for total IgG concentration. The objective of the second study was to evaluate the isolated effect of the colostrum from HT cows on calf immune response and growth performance. The experimental design was identical to the first study, but all calves were born to cows under thermoneutral conditions during the dry period. At birth, calves were blocked by sex and birth weight and then randomly assigned to 1 of 2 treatments, which meant they received pooled colostrum from HT cows or CL cows. No treatment effect was observed on passive immune transfer or on postnatal growth. Thus, heat stress during the last 6 wk of gestation negatively affects the ability of the calf to acquire passive immunity, regardless of colostrum source.

Performance traits and immune response of broiler chicks treated with zinc and ascorbic acid supplementation during cyclic heat stress.

This research was conducted to investigate the effect of supplementation of zinc (Zn) and ascorbic acid (AA) in heat-stressed broilers. A total of 160-day-old broiler chicks of approximately the same weight and appearance were divided into four treatment groups (control, T1, T2, and T3). Control group was fed a standard diet without any supplementation. T1 was supplemented with Zn at the rate of 60 mg/kg of feed, T2 was supplemented with 300 mg/kg of feed AA, and T3 was supplemented with combination of Zn and AA. From week 3 to 5, heat stress environment was provided at the rate of 12 h at 25 °C, 3 h at 25 to 34 °C, 6 h at 34 °C, and 3 h at 34 to 25 °C daily. The results revealed that feed intake, body weight and feed conversion ratio (FCR), and weight of thymus, spleen, and bursa of Fabricius improved significantly (P < 0.05) in T3 compared to the other treatments. Antibody titer against Newcastle disease (ND), infectious bursal disease (IBD), and infectious bronchitis (IB) increased significantly (P < 0.05) in T2 and T3 groups. However, total leucocytes count, lymphocytes, and monocytes increased (P < 0.05) in all treated groups compared to control. The results indicated that the supplementation of Zn or AA alone or in combination improved the performance and immune status of broilers reared under heat stress.

Effects of dietary selenium and vitamin E on immune response and biological blood parameters of broilers reared under thermoneutral or heat stress conditions.

A study was conducted using 360 broiler chickens to evaluate the effects of dietary vitamin E (0, 125 and 250 mg/kg), selenium (Se, 0, 0.5 and 1 mg/kg), or their different combinations on immune response and blood biological parameters of broilers raised under either thermoneutral (TN, 23.9 °C constant) or heat stress (HS, 23.9 to 37 °C cycling) conditions. Humoral immunity was assessed by intravenous injection of 7% sheep red blood cell (SRBC) followed by evaluation of serum for antibody titers in primary and secondary responses. Heterophil to lymphocyte (H/L) ratio also determined as an indicator of stress. Furthermore, at the end of the experiment, birds were bled for determination of some biological parameters. There was a significant reduction in body weight and feed intake, but the feed conversion ratio increased when the birds were exposed to HS (P<0.05). Body weight and feed intake were not influenced significantly by dietary vitamin E and Se (P>0.05), whereas feed conversion was improved significantly by 125 mg/kg vitamin E (P<0.05). The liver and lymphoid organ weights as well as IgM and IgG, antibody titers for primary and secondary antibody responses to SRBC were reduced significantly under HS (P<0.05). Heat stress also resulted in a significant increase in H/L ratio (P<0.05). Dietary vitamin E resulted in improvement of primary and secondary antibody responses both in TN and HS broilers (P<0.05). The HS birds also showed an improved antibody titer in secondary response with high concentration of Se (P<0.05). Vitamin E and Se had interactive effects on anti-SRBC titers; however, no consistent differences were found between dietary levels during the study. The H/L ratio decreased by feeding vitamin E at both levels either under HS or TN conditions (P < 0.05). The serum concentrations of glucose, triglycerides, total cholesterol, and LDL-cholesterol were increased but serum HDL-cholesterol decreased in HS broilers (P<0.05).

Performance, egg quality, and immune response of laying hens fed diets supplemented with mannan-oligosaccharide or an essential oil mixture under moderate and hot environmental conditions.

In total, 432 thirty-six-week-old laying hens were fed a basal diet supplemented with mannan-oligosaccharide (MOS) or an essential oil mixture (EOM) from 36 to 51 wk of age. Hens were divided into 3 equal groups replicated 6 times with 24 hens per replicate. No significant difference was observed among the dietary treatments in terms of performance indices. Different from the dietary manipulation, high environmental temperatures negatively influenced all of the laying performance traits except the feed conversion ratio in association with the diminished feed consumption. The MOS, and particularly the EOM, tended to alleviate the deleterious effect of heat stress on BW gain. Mortality was higher in MOS-fed hens than with other treatments. A supplementation diet with MOS or EOM provided increments in eggshell weight (P < 0.01). Relative albumen weight was significantly decreased (P < 0.05) in response to EOM or MOS supplementation; however, this was not the case in the yolk weight rate. The MOS decreased albumen height and Haugh unit (P < 0.05). High environmental temperatures hampered entire egg quality characteristics except for the eggshell breaking strength and egg yolk weight. These results indicated that heat stress adversely affected both productive performance and egg quality. As for the results of this study, neither MOS nor EOM was efficacious in improving efficiency of egg production and stimulating humoral immune response in laying hens reared under moderate and hot climatic conditions. However, the ameliorative effect exerted by MOS and EOM on eggshell characteristics is conclusive.

Prolonged exposure to hyperthermic stress augments neutrophil recruitment to lung during the post-exposure recovery period.

The effects of heat, especially long-term heat exposure, are complex and incompletely understood and few studies have analysed the immunological consequences of such exposures. In the present study we analysed how long-term hyperthermia modified the pulmonary immune responses, especially recruitment of neutrophils to sites of inflammation, infection and injury. Using our mouse model of long-term whole body hyperthermia (continuous 5-day passive febrile range hyperthermia (5d-FRH)) we found that bacterial lipopolysaccharide (LPS) challenge greatly increased neutrophil accumulation in bronchoalveolar lavage and lung parenchyma in 5d-FRH exposed mice in comparison to LPS-treated controls. Moreover, the effect was sustained, and persisted during the post-exposure recovery period, and LPS challenge on days 5-7 post-recovery also exhibited similarly augmented neutrophil response. Lung lavage from 5d-FRH mice, either immediately or up to 7 days post-exposure, showed significantly increased levels of ELR + CXC chemokines, KC or LIX in response to LPS challenge, indicating that enhanced chemokines could contribute to the increased recruitment of neutrophils to the lung. However, an in vivo neutrophil migration assay following 5d-FRH and during the post-exposure recovery period also showed persistently enhanced neutrophil influx in response to a fixed chemotactic gradient generated by recombinant human IL-8, suggesting that additional mechanisms besides increased ELR + CXC chemokines contributed to the augmented neutrophil response caused by 5d-FRH exposure. These previously unappreciated profound and lasting effects of long-term hyperthermia may have important consequences and may help explain the increased risk of respiratory illnesses in active duty personnel and returning veterans.

Effects of different levels of selenium on growth performance and immunocompetence of broilers under heat stress.

An experiment was undertaken to evaluate the effect of dietary selenium (Se) levels on growth performance and immune competence of broilers under heat stress. Birds were raised in either a thermoneutral (TN, 23.9 degrees C constant) or heat stress conditions (HS, 23.9 degrees C to 38 degrees C cycling) and were fed a corn-soybean meal basal diet supplemented with Se at 0, 0.2 and 0.4 mg/kg. A total of 240 one-day-old male broiler chicks were randomly assigned to six groups; each group had four replicates of 10 birds. Body weight and feed intake were not influenced by dietary Se, while feed conversion was significantly improved by a Se-supplementation of 0.2 mg/kg. HS significantly reduced body weight, feed intake and feed conversion. Numbers of abdominal exudate cells (AEC), percentage of macrophages in AEC, phagocytic macrophages, internalized opsonised and unopsonised sheep red blood cells (SRBC) were significantly increased by dietary Se. Both primary and secondary antibody responses were characterised by increasing titres of antibody to SRBC by dietary Se when birds were exposed to HS (p < 0.05). Lymphoid organ weights, antibody responses, incidence of macrophages in AEC, and phagocytic ability of macrophages were also significantly reduced under HS. These results indicated that HS severely reduced growth performance and immunocompetence of broilers, whereas the immune response of broilers improved by dietary Se supplementation under HS.

Brown seaweed- (Tasco) treated conserved forage enhances antioxidant status and immune function in heat-stressed wether lambs.

Twenty-seven wether lambs were utilized to evaluate select innate immunity and oxidative stress in response to diet and heat stress. Dietary treatments were: (i) control (tall fescue) hay = no Tasco (tradename for the extract of the brown seaweed, Ascophyllum nodosum, Acadian Sealants Ltd, Nova Scotia, Canada); (ii) pre-harvest Tasco-Forage-treated hay and (iii) control hay + post-harvest Tasco-EX. Tasco-Forage and Tasco-EX are two forms of the Tasco extract that are either applied to foliage or used for direct feeding, respectively. All lambs were supplemented with soyabean meal and trace mineralized salt. Heat stress was applied for 10 days with measurements obtained at days 0, 4 and 10. A heat x treatment interaction indicated hay with Tasco enhanced monocyte oxidative burst through short duration (p < 0.05) and long duration (p < 0.10) heat stress. Phagocytic activity was influenced by days of heat stress (p < 0.001) and treatment (p = 0.02) with post-harvest Tasco lambs exhibiting the greatest immune enhancement (p < 0.05). Red and white blood cell glutathione peroxidase increased by heat stress day 10 in Tasco lambs. Superoxide dismutase activity was increased and lipid hydroperoxide metabolites minimized (p < 0.01) through long duration heat stress in the pre-harvest Tasco group. Tasco treatment of tall fescue hay prior to harvest appears to provide residual effects on animal antioxidant availability in short-duration heat stress. Tasco supplementation to post-harvest fescue hay enhances immune function and protects against prolonged heat-induced oxidative stress.

Effects of different levels of zinc on the performance and immunocompetence of broilers under heat stress.

Male broilers were used to evaluate the effect of zinc on performance and immune competence during heat stress (HS). Broilers raised in either a thermoneutral (TN, 23.9 degrees C constant) or HS (23.9 to 35 degrees C cycling) environment were fed a low zinc diet (LZ; 34 mg/kg), an adequate zinc diet (AZ; 68 mg/kg), or a supplemental zinc diet (HZ; 181 mg/kg). Humoral immunity was assessed by intravenous injection of 7% SRBC followed by evaluation of serum for antibody titers in primary and secondary responses. Cell-mediated immunity was assessed using a Sephadex stimulation method to recruit abdominal exudate cells (AEC) to evaluate macrophage phagocytic ability. The HS birds consumed 12.5% less feed, gained 24.6% less weight, and had lower feed efficiency when compared to TN birds. Dietary zinc levels did not impact growth performance or plasma zinc concentration. Numbers of AEC, macrophages in AEC, phagocytic macrophages, and internalized opsonized and unopsonized SRBC were increased by HZ. Total, IgM, and IgG antibody titers for primary and secondary responses were significantly increased in birds receiving HZ under TN conditions. Tibia zinc concentration increased with increasing zinc levels but did not change with temperature. Lymphoid organ weights, primary and secondary antibody responses, incidences of macrophages in AEC, phagocytic ability of macrophages, and plasma zinc concentration were all significantly reduced by HS. These results indicate that the immune response of broilers can be influenced by the level of zinc in the diet and by environmental conditions.

Effect of dietary supplemental levels of vitamin A on the egg production and immune responses of heat-stressed laying hens.

Two experiments were conducted to evaluate the effect of vitamin A supplementation of a commercial layer diet on the laying performance and immune function of heat-stressed hens. In Experiment 1, two different levels of vitamin A supplementation (3,000 and 9,000 IU/kg) were used to investigate the laying performance and antibody titer against Newcastle disease virus (NDV) of heat-stressed hens. Results showed that the high level of vitamin A supplementation (9,000 IU/kg) had a beneficial effect on the feed intake and laying rate of heat-stressed hens (P < 0.05), compared with the control group (3,000 IU/kg). The antibody titers were not influenced by the level of vitamin A (P > 0.05). In Experiment 2, the effect of four levels of vitamin A (3,000, 6,000, 9,000, and 12,000 IU/kg) on the antibody titer to NDV and T lymphocyte proportion was studied. The experimental birds were exposed to a high temperature (31.5 C) 15 d after NDV vaccination (Treatment 1) or immediately (Treatment 2). The results showed that the egg weight was increased (P < 0.01) by the high levels of vitamin A supplementation (6,000 and 9,000 IU/kg), but feed intake, laying rate, and body weight loss were not (P > 0.05). In Treatment 1, vitamin A had no significant effect on antibody titers against NDV in normal or hot environments but increased (P < 0.01) the proportion of alpha-naphthyl acetate esterase (ANAE)-positive cells. Vitamin A supplementation had a significant effect on NDV antibody titer and ANAE-positive cell proportion in Treatment 2 (P < 0.01). The results of the present study suggested that vitamin A supplementation in commercial layer diets to layer chickens under heat stress was beneficial to laying performance and immune function.

Effects of vitamin E and C supplementation on performance, in vitro lymphocyte proliferation, and antioxidant status of laying hens during heat stress.

Vitamin E (dl-alpha-tocopheryl acetate) was evaluated for its effects on performance, lymphocyte proliferation, and antioxidation in layers during heat stress. In Trial 1, 25, 45, or 65 IU of vitamin E/kg were fed to four replicated pens (five hens/cage) of DeKalb Delta or Hy-Line W-36 per treatment starting at 20 wk of age. At 34 wk of age, hens were heat-stressed at diurnal temperature ranging from 21 C to 35 C for 3 wk. The performances of hens not exposed to heat stress were not influenced by supplemental vitamin E. Supplemental vitamin E did not affect egg production; however, egg mass was greater (P < 0.05) with supplementation of 65 IU of vitamin E/ kg during heat stress. Egg yolk was significantly increased (P < 0.04) when hens were fed 45 and 65 lU/kg compared with the control vitamin E level (25 lU/kg). Haugh units were higher (P < 0.01) for hens fed 65 IU of vitamin E/kg compared to 25 and 45 lU/kg. Lymphocyte proliferative responses to concanavalin A (Con A) and Salmonella typhimurium lipopolysaccharide (LPS) were greater (P < 0.0001) in hens fed 45 and 65 IU of vitamin E/kg during heat stress. Strain had no effect on any of the parameters measured. In Trial 2, a 2 x 2 factorial was designed to test effects of vitamin C in drinking water (0 and 1,000 ppm) and dietary vitamin E (25 and 65 IU/kg). Eight replications per treatment with four hens per replication cage were heat-stressed at constant temperature of 35 C for 3 wk. Egg production and egg mass were higher when hens were fed 65 IU of vitamin E/kg than when hens were fed 25 lU/kg (81.5 vs. 75.9%, P < 0.03 and 48.2 vs. 44.6 g, P < 0.03, respectively). Yolk solids weight for the 65 IU vitamin E/kg group was higher (P < 0.01) compared to the 25 IU/kg group. ConA and LPS mitogenic responses were greater in hens fed 65 IU of vitamin E (P < 0.001 or P < 0.003, respectively) or 1,000 ppm of vitamin C (P < 0.001 or P < 0.002, respectively). The combination of 65 IU vitamin E/kg and 1,000 ppm vitamin C showed the highest ConA and LPS mitogenic responses among the treatments. No interaction effects of the two vitamins on production measurements or lymphocyte proliferative responses were observed. TBA values in egg yolk and plasma of hens fed 65 IU of vitamin E/kg were lower (P < 0.0001) than those of hens that received 25 IU of vitamin E/kg. These results suggest that vitamin E supplementation at 65 IU/kg diet may enhance production, induction of in vitro lymphocyte proliferation by ConA and LPS, and antioxidant properties of egg yolks and plasma of White Leghorn hens during heat stress and that supplementation of 1,000 ppm vitamin C may further enhance in vitro lymphocyte proliferative responses of hens during heat stress.