A combination of zinc and pyridoxine supplementation to the diet of laying hens improves performance and egg quality

Dietary vitamin B6 supplementation alleviates heat stress-induced intestinal barrier impairment by regulating the gut microbiota and metabolites in broilers

Heat stress (HS) brings great challenges to the poultry industry. Vitamin B6 (VB6) is an essential micro-nutrient for animals to maintain normal physiological functions and possesses antioxidant and anti-inflammatory properties. This study aimed to explore the effect of VB6 on alleviating HS-induced intestinal barrier impairment in broilers. A total of 250 broilers (609.76 ± 0.34 g) were randomly allocated to 5 groups with 5 replicate cages of 10 birds each. The broilers in thermoneutral (TN) group were raised in thermoneutral conditions (23 ± 1°C) and fed with a basal diet. The birds in other four groups were housed under cycle high temperature (34 ± 1°C for 8 h/d) from d 21 to 35 and fed with the basal diet (HS group) or basal diet supplemented with 6, 12, or 24 mg/kg VB6 (HB-6, HB-12, HB-24 groups). The results showed that HS reduced the growth performance, increased ileum inflammatory cytokines levels, and impaired the gut barrier function (P < 0.05). Compared to the HS group, final body weight, average daily gain, and average daily feed intake, and the feed conversion ratio were improved by VB6 supplementation. The diamine oxidase, interleukin (IL)-1β, tumor necrosis factor-α, IL-18, IL-10, and interferon-γ levels were reduced by VB6 supplementation (P < 0.05). Moreover, VB6 supplementation linearly or quadratically enhanced villus height and villus height-to-crypt depth ratio of duodenum and jejunum, and decreased crypt depth of duodenum and ileum. The mRNA expression of Occlaudin, ZO1, Mucin2, Mucin4, E-cadhein, and β-catenin were increased by VB6 treatment (P < 0.05). Furthermore, dietary VB6 altered the diversity and community of gut microbiota (P < 0.05). A total of 83 differential metabolites associated with the amelioration of VB6 were identified, which were primarily enriched in glycerophospholipid metabolism, caffeine metabolism, and glutathione metabolism pathway. Collectively, VB6 may improve the growth performance and intestinal barrier function of heat-stressed broilers by regulating the ileal microbiota and metabolic homeostasis.

Mitigation of heat stress effects on laying hens' performances, egg quality, and some blood parameters by adding dietary zinc-enriched yeasts, parsley, and their combination

Objective

Finding natural, handy and efficient nutritional solutions to prevent and mitigate negative effects caused by environmental heat stress and to be applied to large-scale laying hen industry.

Research design

A 3-weeks trial was conducted on 128 laying hens TETRA-SL LL (50 weeks of age) housed in 8 cages/group, 4 laying hens/cage, 32 laying hens/group, under heat stress conditions (34±1°C). The basal diet on corn and soybean meal was formulated to be isocaloric and isonitrogenic. Compared to Control group diet (C), experimental groups E1 included 1% zinc-enriched yeast; E2 included 2% parsley and E3 included 1% zinc-enriched yeast combined with 2% parsley to minimize the heat stress effects.

Methods

The parsley and the zinc-enriched yeast were analysed for their chemical composition, total polyphenols, antioxidant capacity, minerals, vitamin E and incorporated into the ration structure. Production parameters, egg quality, biochemical and haematological profiles of blood samples were analysed during the trial.

Results

A statistically significant (p < 0.05) average egg weight was noticed on E2 and E3 compared to Control group, and also during the 1st week compared to the 2nd and the 3rd experimental weeks. Average daily feed intake values were highly significant (p < 0.001) on E3 group compared to C, E1, E2, and on the 2nd week compared to the 3rd experimental week (p < 0.021). Feed conversion rate was highly significant (p < 0.001) during the 2nd and the 3rd experimental weeks compared to the 1st week. The average daily egg production was highly significant (p < 0.001) within 1st week compared to the 2nd and 3rd weeks. A highly significant (p < 0.001) yolk coloration was noticed on E2 and E3 groups. The malondialdehyde (MDA) concentration decreased significantly (p < 0.05) to all experimental groups compared to Control group during the 14th and 28th days of storage.

Conclusion

These findings suggest that the two ingredients minimized the heat stress effects on production performance parameters with a demonstrated antioxidant capacity role by delaying the lipid peroxidation during different storage time periods.

Effect of Dietary Supplemental Zinc on Laying Performance, Egg Quality, and Plasma Hormone Levels of Breeding Pigeons

This study aimed to evaluate the dietary zinc requirement of parental pigeons for better laying and reproductive performance, egg quality, sex hormones, and mineral content in eggs. A total of 160 pairs of healthy American Silver King pigeons were randomly assigned to five treatments of eight replicate cages each with four pairs of birds per cage, and fed a basal diet without zinc supplementation or the basal diet supplemented with 30, 60, 90, and 120 mg of zinc/kg (ZnSO₄·7H₂O). The experiment lasted for 45 days, including two laying cycles. Results indicated the egg production rate (P = 0.081), egg shape index (P = 0.038), egg eggshell percentage (P = 0.070), and zinc and calcium contents (P < 0.01) tended to be affected or significantly affected by zinc addition. They increased quadratically with dietary zinc levels (P < 0.05). Besides, shell thickness (P = 0.069), plasma testosterone (P = 0.008), LH, and carbonic anhydrase contents (P < 0.05) tended to be affected or significantly affected by zinc addition. They increased linearly as dietary zinc level increased (P < 0.05). Compared with the control, 60 mg/kg zinc addition increased egg production rate, egg shape index, zinc and calcium contents in eggshell, and plasma testosterone concentration in pigeons (P < 0.05), and tended to increase the eggshell percentage (P = 0.07). Besides, supplemental 120 mg/kg zinc had higher shell thickness and LH content than control (P < 0.05), but had no difference with 60 mg/kg zinc addition. In conclusion, the supplementation of zinc at the level of 60 mg/kg to basal diet improved laying performance by increasing eggshell quality and sex hormone levels of breeding pigeons.

Comparison of plant extract-derived nano-zinc particles with different zinc sources and effects of different Zn sources on egg yield and quality traits

This study aimed to compare the zinc (Zn) nanoparticles obtained from plant extracts with different zinc sources and to reveal the effects of different Zn sources on growth performance, egg quality traits and blood serum parameters of laying quail. Treatment groups as follows: control and 3 and 6 mg/kg inorganic, organic, and plant extract-derived nano-Zn particles to quail diet supplementation. Animals were fed on experimental diets for 6 weeks. Different Zn sources supplemented into quail diets did not significantly affect live weights (P > 0.05). On the other hand, different Zn sources increased egg yields (P < 0.05). Plant extract-derived nano-Zn supplementations into quail diets increased feed consumption, feed conversion ratio, and egg weights (P < 0.05). However, 6 mg/kg plant extract-derived nano-Zn supplementations reduced egg weights. Different Zn sources did not have any significant effects on egg yolk weight (g) and egg yolk color L*b* values (P > 0.05). For blood serum parameters, 6 mg/kg plant extract-derived nano-Zn supplementations increased blood serum AST, ALT, and Zn values (P < 0.05). No adverse effect was observed on the measured values in laying Japanese quails. The findings suggest that plant extract-derived nano-Zn particles could reliably be used in quail feeding.

Meta-analysis of Zinc Supplementation on Laying Performance, Egg Quality Characteristics, and Blood Zinc Concentrations in Laying Hens

There are inconsistent results on the influence of zinc (Zn) supplementation levels on productive indices of laying hens. This study, therefore, uses meta-analysis to synthesis evidence on the effect of inclusion of Zn in chicken diets on performance, egg quality, and blood Zn status of laying hens. Eleven studies were identified and used to analyze the effect of diets with or without Zn supplementation on feed intake, feed conversion ratio (FCR), hen day egg production (HDEP), egg weight (EW), egg mass (EM), Haugh unit (HU) scores, eggshell thickness (EST), eggshell weight (ESW), and blood Zn concentrations in laying hens. Data extracted from the 11 studies included in the meta-analysis were pooled using a random-effects model and expressed as standardized mean differences (SMDs) at a 95% confidence interval (CI). Results indicate that dietary Zn supplementation reduced FCR (SMD =  - 0.50 g feed/g egg; 95% CI: - 0.68 to - 0.31) and increased HDEP (SMD = 0.33%; 95% CI: 0.18 to 0.48), EW (SMD = 0.14 g; 95% CI: 0.03 to 0.25) and EM (SMD = 0.58 g/hen/day; 95% CI: 0.22 to 0.95), HU (SMD = 0.64; 95% CI: 0.42 to 0.85), EST (SMD = 0.84 mm; 95% CI: 0.45 to 1.23), and plasma Zn concentration (SMD = 4.20 mg/dl; 95% CI: 2.99 to 5.40) compared with the controls. In contrast, feed intake and ESW were not significantly different from controls. Restricted subgroup analysis indicated that chosen moderators (age of hen, inclusion level, chicken breed/strain, and supplementation duration) influenced the results of this meta-analysis. There was evidence of significant heterogeneity, and meta-regression indicated that moderators explained most of the sources of heterogeneity. We conclude that dietary zinc supplementation had positive effect on feed conversion ratio, laying performance, aspects of egg quality traits, and blood zinc concentrations in laying hens. The findings from this meta-analysis will help in policy advancements and sustainable use of zinc in the egg production industry.

The Effects of Nano and Micro Particle Size of Zinc Oxide on Performance, Fertility, Hatchability, and Egg Quality Characteristics in Laying Japanese Quail

The current trial was conducted by using the 288 Japanese quails to evaluate the effects of a zinc-deficient diet supplemented with nano and micro zinc oxide on performance, fertility, hatchability, and egg quality characteristics. In this experiment, birds were randomly allocated to 9 dietary treatments includes diets supplemented with nano or micro particles of zinc oxide (amount of ZnO supplement for each treatment) to supply 49, 74, 99, and 124 mg zinc per kilogram of diet in a factorial arrangement (2 × 4) and a control non supplemented diet (24 mg/kg) with four replicates of eight birds (six females and two males) in each pen. Birds were fed the experimental diets from 47 to 75 days of age and had free access to water and feed during the experimental period. Results showed that Zn supplementation, regardless of particle size, improved the eggshell thickness (P < 0.01). A significant (P < 0.05) interaction was observed between zinc level and ZnO particle size for Shell breaking strength. Quails fed diets supplement with ZnO showed significantly higher egg weight and eggshell surface (P < 0.05) as compared with birds fed a non-supplemented control diet. Results obtained here showed that supplementation of nano ZnO enhanced fertility considerably. Application of non-linear quadratic models showed that the maximum egg production percentage was achieved when 67 or 72 mg/kg of dietary zinc was supplied from nano and micro ZnO, respectively. This result indicated that nano ZnO could reduce the zinc requirement in laying Japanese quail.

Production performance, egg quality and some blood parameters of heat-stressed laying hens as affected by dietary supplemental Vit B6, Mg and Zn

OBJECTIVES

The effects of dietary supplements, including magnesium sulfate (Mg), zinc oxide (Zn) and vitamin B6 (Vit B6), on the performance of laying hens reared under normal (NC) and heat-stress (HSC) conditions were investigated.

MATERIAL AND METHODS

A total of 288 30-week-old Lohmann LSL-Lite laying hens were randomly divided into 48 cages and assigned to receive one of the eight diets with six replicates and six hens per replicate, based on a 2 × 2 × 2 factorial arrangement of treatments. Dietary supplements, including two levels (0 & 600 mg/kg) of Mg, two levels (0 & 30 mg/kg) of Zn and two levels (0 & 8 mg/kg) of Vit B6, in normal and heat-stress conditions, were tested at 30-40 and 41-45 weeks of age, respectively.

RESULTS

In the Vit B6 group, a decrease in feed intake (FI), egg production (EP), albumin, Zn, Fe and Mg, and an increase in triglyceride and insulin in HSC were observed, in addition to a decrease in cholesterol and an increase in egg weight (EW) in NC. Supplemental Mg decreased EP, blood triglycerides and copper in NC, and Zn, Fe and Mg in HSC as well. Feeding Zn, increased egg shape index, total protein and copper in addition to yolk index in NC and Fe in HSC. EWs were higher in hens supplemented with Vit B6+Mg in HSC. Increased insulin and decreased glutathione peroxidase activity were detected with the Vit B6+Zn compared to feeding either Vit B6 or Zn in HSC.

CONCLUSIONS

The results indicated Vit B6 could improve EWs and suppress blood cholesterol in NC. Zn improved the egg shape index in NC.

Environmental Stress in Chickens and the Potential Effectiveness of Dietary Vitamin Supplementation

Environmental stressors can promote the vulnerability of animals to infections; it is therefore, essential to understand how stressors affect the immune system, the adaptive capacity of animals to respond, and effective techniques in managing stress. This review highlights scientific evidence regarding environmental stress challenge models and the potential effectiveness of vitamin supplementation. The major environmental stressors discussed are heat and cold stress, feed restriction, stocking density, and pollutants. Much work has been done to identify the effects of environmental stress in broilers and layers, while few involved other types of poultry. Studies indicated that chickens' performance, health, and welfare are compromised when challenged with environmental stress. These stressors result in physiological alterations, behavioral changes, decreased egg and meat quality, tissue and intestinal damage, and high mortalities. The application of vitamins with other nutritional approaches can help in combating these environmental stressors in chickens. Poultry birds do not synthesize sufficient vitamins during stressful periods. It is therefore suggested that chicken diets are supplemented with vitamins when subjected to environmental stress. Combination of vitamins are considered more efficient than the use of individual vitamins in alleviating environmental stress in chickens.

Effects of Dietary Zinc on Performance, Zinc Transporters Expression, and Immune Response of Aged Laying Hens

This study was to investigate the effects of dietary zinc (Zn) supplementation on performance, zinc transporter gene expression, and immune function in aged laying hens. In experiment 1, twenty 31-week-old hens (young) and twenty 60-week-old hens (old) with the same genetic background were fed with the same diet for 4 weeks. In experiment 2, a basal diet supplemented with zinc sulfate (ZnS) and zinc glycine chelate (ZnG) at 30, 60, 90, and 120 mg Zn/kg to constitute nine experimental diets. Eight hundred and ten 60-week-old layers were distributed in a completely randomized experimental design with 9 treatments, 6 replicates of 15 birds each, and birds were fed for 10 weeks. In experiment 1, results showed that zinc and metallothionein (MT) concentration in the shell gland of old hens was significantly lower than young layers (P < 0.05). Zinc transporters ZnT1, 4, 5, 6, and 7 messenger RNA (mRNA) abundance in old layers were significantly lower versus the young (P < 0.05). In experiment 2, results indicated that dietary zinc supplementation did not significantly affect the laying rate, average feed intake, egg weight, feed conversion efficiency, broken egg rate, or mortality (P > 0.05). Supplemental ZnG significantly improved eggshell breaking strength than ZnS, with a higher alkaline phosphatase (ALP) activity and more abundant ZnT4 expression in shell gland versus ZnS (P < 0.05). ZnG supplementation at 90 mg Zn/kg affected the duodenal mucus by significantly increasing ZnT1, 6, 7, ZIP13, and MT-4 mRNA level (P < 0.05). Zinc level significantly increased bovine serum albumin (BSA) antibody concentration on 14 day after BSA injection (P < 0.05). Supplementation of ZnG improved eggshell quality of aged layers by upgrading zinc transporter expression in the shell gland and intestine also enhanced humoral immunity.

Strategies to Combat Heat Stress in Broiler Chickens: Unveiling the Roles of Selenium, Vitamin E and Vitamin C

Heat stress compromises efficient poultry production by impairing growth performance and increasing mortality. Mechanisms to dissipate excess heat divert energy from efficient production. This includes increased energy expenditure for respiration, oxidative stress and micronutrient absorption. The fortification of diets with particular feed additives has been known as one of the most important approaches to minimize the negative impacts of heat stress on broiler production. In this context, the promising functional feed additives appeared to be selenium and vitamins E and C. The fortification of broiler diets with these feed additives has been proven to enhance the function of vital organs, immune system response and growth performance of broilers under heat stress. The current review highlights recent successful experiences in the alleviation of heat stress symptoms in broilers using the above-mentioned additives. Selenium and vitamins E and C enhanced production performance in broiler chickens challenged with acute heat stress. The combination of these additives, by employing multiple mechanisms and through synergistic effects, improves heat stress symptoms more efficiently than their individual forms. Emerging literature reveals that selenium and vitamins E and C are involved in close interactions to protect proteins and lipids from oxidative damage and boost immune system function.

Zinc requirements of broiler breeder hens

One hundred and twenty Cobb 500 hens, 20 wk of age, were randomly allocated into individual cages with the objective of estimating their Zn requirements. The study was composed of 3 phases: adaptation to cages (basal diet), depletion (deficient diet containing 18.7 ± 0.47 ppm Zn) for 7 wk, and experimental phases. Hens were fed diets with graded increments of Zn sulfate heptahydrate (ZnSO4·7H2O), totaling 18.7 ± 0.47, 50.3 ± 10.6, 77.3.0 ± 11.0, 110.2 ± 12.8, 140 ± 12.2, and 170.6 ± 13.2 ppm analyzed Zn in feeds for 12 wk (experimental phase). Requirements of Zn were done using quadratic polynomial (QP), broken line quadratic (BLQ), and exponential asymptotic (EA) models. In general, the non-linear statistical models were the ones that best fit the results in this study. Requirements obtained for hen day egg production and settable egg production were 83.3, 78.6 ppm and 61.4, 65.4 ppm for period of 33 to 36 wk, and 63.3, 53.1 and 60.4, 46.1 ppm for period of 37 to 40 wk, and 62.8, 52.8, and 67.7, 62.1 ppm for period of 41 to 44 wk, respectively, using BLQ and EA models. Total eggs and total settable eggs produced per hen had Zn requirements estimated as 75.7, 64.7 ppm, and 56.5, 41.5 ppm, respectively, for BLQ and EA models, whereas for alkaline phosphatase and eggshell percentage were 161.8, 124.9 ppm and 126.1, 122.4 ppm, using QP and BLQ models. Maximum responses for Zn in yolk for periods of 37 to 40 and 41 to 44 wk were 71.0, 78.1 and 64.5, 59.6 ppm, respectively, using BLQ and EA models. Breaking strength had Zn requirements estimated at 68.0 and 96.7 ppm, whereas eggshell palisade layer and eggshell thickness were maximized with 67.9, 67.9 ppm, and 67.7, 64.4 ppm, respectively, for BLQ and EA models. The average of all Zn requirement estimates obtained by EA and BLQ models in the present study was 72.28 ppm or 11.1 mg/hen/d.

Optimization of dietary zinc for egg production and antioxidant capacity in Chinese egg-laying ducks fed a diet based on corn-wheat bran and soybean meal

The aim of this study was to evaluate the effect of zinc supplementation on productive performance and antioxidant status in laying ducks. Five-hundred-four laying ducks were divided into 7 treatments, each containing 6 replicates of 12 ducks. The ducks were caged individually and fed a corn-soybean meal and wheat bran basal diet (37 mg Zn/kg) or the basal diet supplemented with 15, 30, 45, 60, 75, or 90 mg Zn/kg (as zinc sulfate). During the early laying period of 10 d (daily egg production <80%), egg production, daily egg mass, and FCR increased quadratically with increasing dietary Zn levels (P < 0.05). The highest egg production and daily egg weight were obtained when 30 or 45 mg Zn/kg diet was supplemented, with lowest FCR. Similarly, the highest egg production and daily egg mass were observed in the group supplemented with 30 or 45 mg Zn/kg during the peak laying period of the subsequent 120 d (daily egg production >80%). Average egg weight and feed intake did not differ among the groups of graded Zn supplementation.The egg quality was not affected by dietary Zn, including the egg shape index, Haugh unit, yolk color score, egg composition, and shell thickness. The activities of plasma activities of total superoxide dismutase (T-SOD) and glutathione peroxidase (GSH-PX) increased in a quadratic manner (P < 0.001) with increasing supplemental Zn. Plasma concentration of Zn increased quadratically (P < 0.05) as dietary Zn increased. The hepatic activity of Cu/Zn-SOD and GSH-PX increased quadratically (P < 0.05) with increasing dietary Zn. Plasma Zn concentrations were positively correlated with activities of T-SOD (P < 0.05), and positively with plasma Cu. Plasma concentration of reduced glutathione was correlated with plasma Cu. In conclusion, supplementation of Zn at 30 or 45 mg/kg to a corn-wheat bran and soybean basal diet may improve the productive performance and enhance the antioxidant capacity.

Nutritional requirements of meat-type and egg-type ducks: what do we know?

The demand for duck meat, duck eggs, and associated products is increasing each year. Classic and modern selection programs have been applied to enhance the economic traits of ducks to satisfy the requirements of consumers and enhance the incomes of producers. The nutritional requirements of unselected ducks may not be adequate, however, to fulfill the potential productivity performance of modern birds, including both meat-type and egg-type ducks. In particular, an imbalanced diet is associated with low productive performance and signs of nutritional deficiency (if insufficient nutrients are supplied), as well as with high feed costs and manure problems that reflect flock health and welfare (if excessive nutrients are supplied). Thus, the main aim of this review is to summarize the results of previous studies that estimated the nutrient requirements of meat-type and egg-type ducks in order to evaluate current knowledge and to identify further issues that need to be addressed. In addition, the results obtained in previous studies are compared in order to understand how to lower commercial feed costs, fulfill the genetic potential of selected ducks, protect the environment from pollution, and satisfy the welfare and health needs of ducks.

Single and combined effects of zinc and cinnamon essential oil in diet on productive performance, egg quality traits, and blood parameters of laying hens reared under cold stress condition

This study was conducted to evaluate the effects of adding zinc (Zn), cinnamon essential oil (Ci), or their combination in diet on productive performance, egg quality, and blood parameters of laying hens reared under cold stress condition (8.8 ± 3 °C). Feed intake (FI), feed conversion ratio (FCR), egg weight (EW), egg production (EP), and egg mass (EM) were evaluated during the 56-day trial period using 120 Lohmann LSL-Lite laying hens. Significant interactions between Ci and Zn on FCR, EW, EP, or EM were observed (P < 0.05). The EP, EM, and EW increased, whereas FCR decreased (P < 0.05) in the hens fed the diets including Ci and Zn (as single or combined form) compared to those fed the basal diet. There were significant interactions between Ci and Zn on the serum level of glucose and triglycerides as well as plasma concentration of zinc (P < 0.05), so that serum content of glucose and triglyceride decreased and the plasma content of zinc increased in the hens fed the diets including Ci and Zn (together) compared to those fed the basal diet. From the results of the present experiment, it can be concluded that diet supplementation by the combined form of Ci and Zn could have beneficial effects on performance and blood parameters of hens reared under cold stress condition.

Effect of sex and dietary organic zinc on growth performance, carcass traits, tissue mineral content, and blood parameters of broiler chickens

Zinc (Zn) is an essential mineral for animal development and function. A study was carried out to evaluate the effect of sex and dietary organic zinc (OZ) on growth performance, carcass traits, tissue mineral content, and blood parameters of broiler chickens. A total of 240 1-day-old male and 240 female broiler chicks (Cobb × Cobb) were assigned to two dietary levels of OZ (2 × 2 factorial) with six replicates per treatment (20 birds/replicate pen). The OZ supplementation levels were 0 and 25 ppm. Results showed that OZ supplementation did not affect the growth performance of male and female broilers, but the males showed significantly better (P < 0.05) growth performance than females did. Similarly, OZ supplementation did not affect the thickness of both the back and thigh skin of male and female broilers; however, males had thicker skin than females. Dietary OZ supplementation did not affect collagen contents in the skin and meat samples. Male broilers had higher skin collagen contents than females, but no sex difference was found in meat collagen contents. OZ supplementation did not affect the shear force values of skin and meat samples. Male broilers had higher shear force values of back skin than females, but not in the meat samples. Dietary OZ supplementation increased (P < 0.05) the thigh meat Zn content in both sexes. The plasma Ca content was significantly (P < 0.05) increased by dietary OZ supplementation; however, other blood parameters were not affected by dietary OZ supplementation. Males had higher plasma glucose and cholesterol content than females. It is concluded that dietary OZ supplementation at the level of 25 ppm does not affect the growth performance and skin quality of broiler chickens but increases the Zn content in thigh meat and Ca content in plasma of broiler chickens. Male broilers had better growth performance and skin quality than females.

Zinc as a feed supplement and its impact on plasma cholesterol concentrations in breeding cocks

The aim of this work was to verify the impact of feed supplemented with selected inorganic and organic zinc compounds on the total cholesterol concentrations and other blood plasma indices in breeding cocks. A total of 250 RIR 05 breeding cocks, 9 weeks old, were used. The cocks were divided into 5 groups of 50 animals each (four experimental groups and one control group). Cocks were fed a commercial feed mixture specifically for breeding cocks, containing 30.4 mg·kg-1 of zinc. The feed for experimental groups of cocks was fortified to 100 mg Zn·kg-1: zinc sulphate in first group, zinc oxide in second group, fodder yeast (Minvital Zn) in third group and Bioplex Zn in fourth group. Blood samples for biochemical examination were taken from the basilic vein. The contents of total cholesterol (Chol), total proteins (TP), glucose (Glu), aspartate aminotransferase (AST), alanine aminotransferase (ALT), calcium (Ca), phosphorus (P) and magnesium (Mg) in blood plasma were spectrophotometrically measured using a biochemical analyser, Cobas EMira, and commercial kits (Biovendor a.s., Czech Republic). In the 15th week of age, third and fourth groups showed a significant (P ≤ 0.05) and highly significant (P ≤ 0.01) decrease of total cholesterol in blood plasma compared to the control. In the 20th and 25th week of age, all of the experimental groups showed a significantand highly significant (P ≤ 0.01) decrease of total cholesterol in blood plasma compared to the control. Other monitored indices (total proteins, glucoses, aspartate aminotransferase, alanine aminotransferase, calcium, phosphorus and magnesium) did not reveal any significant changes between the experimental and the control groups. The presented work provides the first available experimental evidence regarding the impact of zinc supplementation on the cholesterol levels in blood plasma of breeding cocks.

Role of dietary zinc in heat-stressed poultry: a review

High ambient temperatures compromise performance and productivity through reducing feed intake and decreasing nutrient utilization, growth rate, egg production, egg quality, and feed efficiency, which lead to economic losses in poultry. Environmental stress also leads to oxidative stress associated with a reduced antioxidant status in the bird in vivo, as reflected by increased oxidative damage and lowered plasma concentrations of antioxidant vitamins (e.g., vitamins E, A, and C) and minerals (e.g., Zn). Zinc has an important role in numerous biological processes in avian and mammalian species. For instance, Zn is an essential component of many enzymes, and it has both structural and catalytic functions in metalloenzymes. Furthermore, dietary Zn is required for normal immune function as well as proper skeletal development and maintenance. One of the most important functions of Zn is related to its antioxidant role and its participation in the antioxidant defense system. This work compiles past and present information about the role of Zn in heat-stressed poultry health.