Liyang Zhang

Dietary Manganese Modulates Expression of the Manganese-Containing Superoxide Dismutase Gene in Chickens

To investigate the possible mechanism(s) by which dietary manganese (Mn) levels and sources modulate the expression of the manganese-containing superoxide dismutase (MnSOD) gene at both the transcriptional and translational levels, we used 432 8-d-old male broiler chicks in a 1 plus 4 × 2 design. Chickens were given either a diet without Mn supplementation [control (C)] or diets supplemented with 100 (optimal) or 200 (high) mg Mn/kg diet from inorganic Mn sulfate (I) or 3 organic complexes of Mn and amino acids with weak (W), moderate (M), or strong (S) chelation strength up to 21 d of age. Compared with C chicks, chicks fed Mn-supplemented diets had higher (P < 0.01) Mn concentrations, specificity protein 1 (Sp1) DNA-binding activities, MnSOD mRNA levels, MnSOD mRNA-binding protein (MnSOD-BP) RNA-binding activities, MnSOD protein concentrations, and MnSOD activities within heart tissue, but lower (P < 0.01) heart activating protein-2 (AP-2) DNA-binding activities. Chicks fed M diets had higher (P < 0.05) heart Mn concentrations, MnSOD mRNA levels, and MnSOD-BP RNA-binding activities compared with those fed the I and W diets and lower (P < 0.01) AP-2 DNA-binding activities than those fed other treatment diets. These results suggest that dietary Mn could modulate the expression of the MnSOD gene in broilers by altering Sp1 and AP-2 DNA-binding activities at the transcriptional level and enhancing MnSOD-BP RNA-binding activity at the translational level. Additionally, an organic Mn source with moderate chelation strength could be more effective than other Mn sources in activating MnSOD gene expression at both the transcriptional and translational levels.

Effects of supplemental zinc source and level on growth performance, carcass traits, and meat quality of broilers

The objective of this study was to investigate the effects of dietary supplemental Zn on growth performance, carcass traits, and meat quality of broilers. Dietary treatments included the corn-soybean meal-based diet (control) and the basal diet supplemented with 60, 120, or 180 mg of Zn/kg as ZnSO(4), Zn amino acid A, Zn proteinate B, or Zn proteinate A. The results showed that birds fed diets supplemented with Zn had higher ADFI, ADG, and percentage of eviscerated yield than birds fed the control diet. Supplemental Zn significantly increased the redness value in breast muscle and pH values in thigh muscle, decreased shear force in thigh muscle, and decreased drip loss in breast and thigh muscle. The DM and intramuscular fat contents of the breast muscle in broilers fed diets with supplemental Zn were higher than those of the control. Results from this study indicated that Zn could promote growth and improve production performance of broilers independent of Zn source.

Differential Expression of Heat Shock Transcription Factors and Heat Shock Proteins after Acute and Chronic Heat Stress in Laying Chickens (Gallus gallus)

Heat stress due to high environmental temperature negatively influences animal performances. To better understand the biological impact of heat stress, laying broiler breeder chickens were subjected either to acute (step-wisely increasing temperature from 21 to 35°C within 24 hours) or chronic (32°C for 8 weeks) high temperature exposure. High temperature challenges significantly elevated body temperature of experimental birds (P<0.05). However, oxidation status of lipid and protein and expression of heat shock transcription factors (HSFs) and heat shock proteins (HSPs) 70 and 90 were differently affected by acute and chronic treatment. Tissue-specific responses to thermal challenge were also found among heart, liver and muscle. In the heart, acute heat challenge affected lipid oxidation (P = 0.05) and gene expression of all 4 HSF gene expression was upregulated (P<0.05). During chronic heat treatment, the HSP 70 mRNA level was increased (P<0.05) and HSP 90 mRNA (P<0.05) was decreased. In the liver, oxidation of protein was alleviated during acute heat challenge (P<0.05), however, gene expression HSF2, 3 and 4 and HSP 70 were highly induced (P<0.05). HSP90 expression was increased by chronic thermal treatment (P<0.05). In the muscle, both types of heat stress increased protein oxidation, but HSFs and HSPs gene expression remained unaltered. Only tendencies to increase were observed in HSP 70 (P = 0.052) and 90 (P = 0.054) gene expression after acute heat stress. The differential expressions of HSF and HSP genes in different tissues of laying broiler breeder chickens suggested that anti-heat stress mechanisms might be provoked more profoundly in the heart, by which the muscle was least protected during heat stress. In addition to HSP, HSFs gene expression could be used as a marker during acute heat stress.

Effects of acute and chronic heat stress on plasma metabolites, hormones and oxidant status in restrictedly fed broiler breeders

Heat tolerance can be improved by feed restriction in broiler chickens. It is unknown whether the same is true for broiler breeders, which are restrictedly fed. Therefore, the current study was conducted to study the effects of heat stress on plasma metabolites, hormones, and oxidative status of restricted fed broiler breeders with special emphases on the temperature and latency of heat exposure. In trial 1, 12 broiler breeders were kept either in a thermoneutral chamber (21°C, control, n = 6) or in a chamber with a step-wise increased environmental temperature from 21 to 33°C (21, 25, 29, 33°C, heat-stressed, n = 6). Changes in plasma total cholesterol, glucose, and triiodothyronine (T3) were closely related to the environmental temperature. When the temperature reached 29°C, plasma T3 (P < 0.05) was significantly decreased in acute heat-stressed birds, whereas plasma glucose (P < 0.001) and cholesterol (P = 0.002) increased only when the temperature reached 33°C. Plasma triglyceride (P = 0.026) and creatine kinase (CK, P = 0.018) were lower in heat-stressed birds than controls regardless of the temperatures applied. In Trial 2, 24 broiler breeders were divided into 2 groups and raised under 21°C and 32°C for 8 weeks, respectively. Total cholesterol was increased in chronic heat-stressed broiler breeders after 4 weeks. Plasma lactate dehydrogenase (LDH, P = 0.047) and glutamic-oxaloacetic transaminase (GOT, P = 0.036) was up-regulated after 6 weeks of thermal treatment, whereas plasma CK (P = 0.009) was increased at the end of thermal treatment. Plasma malonaldehyde, protein carbonyl content, activity of total superoxide dismutase (SOD), and corticosterone content were not altered after acute and prolonged heat challenges. Taken together, acute heat stress primarily resulted in disturbance of plasma metabolites, whereas chronic heat stress caused tissue damage reflected by increased plasma LDA, GOT, and CK. During acute heat stress, plasma metabolites were minimally disturbed in broiler breeders until the environmental temperature reached 33°C.

Manganese source affects manganese transport and gene expression of divalent metal transporter 1 in the small intestine of broilers

In the present study, two experiments were conducted to investigate the effect of Mn source on Mn transport and the expression of a Mn transporter, divalent metal transporter 1 (DMT1), in the small intestine of broilers. In Expt 1, in situ ligated duodenal loops from Mn-deficient chicks (29-d-old) were perfused with solutions containing 0-8.74 mmol Mn/l from either MnSO4, or one of two organic chelates of Mn and amino acids with moderate (OM) or strong (OS) chelation strength (Q(f)) up to 30 min. In Expt 2, Mn-deficient intact broilers (14-d-old) were fed a control diet (12.45 mg Mn/kg) or the control diet supplemented with 100 mg Mn/kg as one of all Mn sources for 14 d. The uptake kinetics of Mn from different Mn sources in the ligated duodenal loops followed a saturable process as determined by regression analysis of concentration-dependent uptake rates. The maximum transport rate (Jmax) and K(m) values, and DMT1 mRNA levels in the ligated duodenal loops were higher (P < 0.01) for OM and OS than for MnSO4. DMT1 mRNA levels were much higher (P < 0.01) in the duodenum than in the jejunum and ileum. Both DMT1 mRNA levels in the duodenum and plasma Mn contents from the hepatic portal vein of intact chicks on day 14 post-feeding increased (P < 0.05) in the following order: control < MnSO4 < OM < OS. These results indicated that organic Mn sources with stronger Q(f) showed higher Mn transport and absorption, and DMT1 might be involved in the regulation of organic Mn transport in the proximal small intestine of broilers.

Effects of supplemental zinc source and level on antioxidant ability and fat metabolism-related enzymes of broilers

The objective of the present study was to investigate the effects of dietary supplemental Zinc (Zn) source and level on antioxidant ability and fat metabolism-related enzymes of broilers. Dietary treatments included the Zn-unsupplemented corn-soybean meal basal diet (control) and basal diets supplemented with 60, 120, or 180 mg Zn/kg as Zn sulfate, Zn amino acid chelate with a weak chelation strength of 6.5 quotient of formation (Qf) (11.93% Zn) (Zn-AA W), Zn proteinate with a moderate chelation strength of 30.7 Qf (13.27% Zn) (Zn-Pro M), or Zn proteinate with an extremely strong chelation strength of 944.0 Qf (18.61% Zn) (Zn-Pro S). The results showed that dietary supplemental Zn increased (P < 0.01) Zn contents in the liver, breast, and thigh muscles of broilers, and up-regulated mRNA expressions of copper and Zn containing superoxide dismutase (CuZnSOD) and metallothioneins (MT) in the liver (P < 0.01) and thigh muscle (P < 0.05), and also enhanced (P < 0.05) CuZnSOD activities in the breast and thigh muscles, which exerted antioxidant ability and a decreased malondialdehyde (MDA) level in the liver (P < 0.01) and breast and thigh muscles (P < 0.05) of broilers. Furthermore, supplemental Zn increased activities of malate dehydrogenase (MDH) and lipoprotein lipase (LPL) in the abdominal fat (P < 0.05), and fatty acid synthetase (FAS) and LPL in the liver (P < 0.01), which were accompanied with up-regulation (P < 0.01) of the mRNA expressions levels of these enzymes in the abdominal fat and liver of broilers. Dietary Zn source, and an interaction between Zn source and level, had no effects on any measurements. It is concluded that dietary Zn supplementation improved Zn status and resulted in promoting antioxidant ability and activities and gene expressions of fat metabolism-related enzymes of broilers regardless of Zn source and level, and the addition of 60 mg Zn/kg to the corn-soybean meal basal diet (a total dietary Zn of approximately 90 mg/kg) was appropriate for improving the above aspects of broilers.

Relative bioavailability of iron proteinate for broilers fed a casein-dextrose diet

An experiment was carried out to determine the bioavailability of organic Fe as Fe proteinate (Alltech, Nicholasville, KY) relative to inorganic Fe source (FeSO4•7H2O) for broiler chicks fed a casein-dextrose diet. A total of 448 1-d-old Arbor Acres commercial male broiler chicks were randomly allotted to 1 of 8 replicate cages (8 chicks per cage) for each of 7 treatments in a completely randomized design involving a 2 × 3 factorial arrangement of treatments with 2 Fe sources (Fe proteinate and Fe sulfate) and 3 levels of added Fe (10, 20, or 40 mg of Fe/kg) plus a Fe-unsupplemented control diet containing 4.56 mg of Fe/kg by analysis. Feed and distilled-deionized water were available ad libitum for an experimental phase of 14 d. At 14 d of age, blood samples were collected for testing hemoglobin (Hb) and hematocrit, and calculating total body Hb Fe, whereas liver and kidney samples were excised for Fe analyses. The results showed that ADG, ADFI, blood Hb, hematocrit, and total body Hb Fe and Fe concentrations in liver and kidney increased linearly (P < 0.0001), whereas mortality decreased linearly (P < 0.0001) as dietary Fe level increased. However, only blood Hb concentration and total body Hb Fe differed (P < 0.004) between the 2 Fe sources. Based on slope ratios from the multiple linear regression of Hb concentration and total body Hb Fe on daily intake of analyzed dietary Fe, the bioavailability of Fe proteinate relative to FeSO4•7H2O (100%) was 117 and 114%, respectively (P < 0.009). The results indicated that blood Hb concentration and total body Hb Fe were sensitive indices in reflecting differences in bioavailability among different Fe sources, and Fe proteinate was significantly more available to broilers than inorganic Fe sulfate in enhancing Hb concentration and total body Hb Fe.

Optimal dietary zinc levels of broiler chicks fed a corn–soybean meal diet from 22 to 42 days of age

An experiment was conducted to investigate the effect of dietary zinc (Zn) level on growth performance, Zn concentration, Zn metalloenzyme activity, Zn transporter 2 (ZnT2) mRNA abundance, metallothionein (MT) mRNA abundance and MT concentration in either serum or tissues, so as to evaluate the optimal dietary Zn level of broiler chicks fed a corn–soybean meal diet from 22 to 42 days of age. At 22 days of age, 288 birds were assigned randomly by bodyweight to one of eight dietary treatments of six replicate cages each with six birds per cage, and fed a Zn-unsupplemented basal corn–soybean meal diet containing 27.66 mg of Zn/kg or the basal diet supplemented with 20, 40, 60, 80, 100, 120 or 140 mg of Zn/kg from reagent-grade ZnSO4·7H2O. Regression analysis was performed to estimate the optimal dietary Zn level in the presence of asymptotic response. The results showed that dietary Zn level had no effect (P > 0.25) on the growth performance, serum alkaline phosphatase and 5′-nucleotidase activities, and liver copper-Zn superoxide dismutase activity, but affected (P < 0.07) tibia Zn concentration, pancreas Zn concentration, ZnT2 mRNA abundance, MT mRNA abundance and MT concentration. The optimal dietary Zn requirements of broilers from 22 to 42 days of age were 62.44 mg/kg for tibia Zn, 64.30 mg/kg for ZnT2 mRNA abundance and 53.50 mg/kg for MT mRNA abundance based on asymptotic models, respectively. Accordingly, the optimal dietary Zn level for broilers from 22 to 42 days of age was 65 mg/kg in this study.

Estimation of standardized phosphorus retention for corn, soybean meal, and corn-soybean meal diet in broilers

Two experiments were conducted to estimate standardized phosphorus (P) retention (SPR) of corn, soybean meal (SBM), and corn-soybean meal (C-SBM) diet in broilers and verify the additivity of SPR for feed formulation of broilers. In total, ninety-six 22-d-old male broilers with similar BW were used in each experiment. After 3 d of acclimation, chicks were fasted for 24 h and then fed P-free, corn, SBM, or C-SBM diets, respectively for 4 h in experiment 1 or 72 h in experiment 2. In experiment 1, the results showed that the excreta collection time of 52 h (48 h after feed withdrawal) was adequate for the estimation of SPR. The basal endogenous P loss (EPL) of chicks fed the P-free diet was estimated to be 123±7 mg/52 h per bird. The values of SPR corrected by basal EPL were 37.6 and 50.5% for corn and SBM, respectively. The determined value of SPR of the C-SBM diet was very close (P>0.79) to the predicted summation of SPR from corn and SBM (44.4 vs. 43.5%). In experiment 2, the results showed that the excreta collection time of 96 h (24 h after feed withdrawal) was sufficient for the estimation of SPR. The basal EPL of chicks fed the P-free diet was estimated to be 85.4±4.0 mg/96 h per bird. The values of SPR corrected by basal EPL were 40.2 and 52.9% for corn and SBM, respectively. The determined value of SPR of the C-SBM diet was lower (P<0.001) than the predicted summation of SPR from corn and SBM (39.7 vs. 46.0%), which might be due to the effect of higher total P intake. The results from the current study demonstrated that the P-free diet could be used for measuring basal EPL in broilers and then estimating the SPR values of feedstuffs for broilers. However, the additivity of SPR in the diet formulation needs to be studied further.

Effects of inorganic and organic manganese supplementation on gonadotropin-releasing hormone-I and follicle-stimulating hormone expression and reproductive performance of broiler breeder hens.

Manganese is an essential microelement. Manganese deficiency affects reproduction performance and reproductive hormones in layers. However, little is known about its effects and the possible mechanism in regulating reproduction in broiler breeder hens. In the current study, broiler breeder hens at peak production were fed with diets supplemented with 0, 120, or 240 mg of Mn/kg as MnSO4 or Mn proteinate for 13 wk. Manganese supplementation did not alter egg laying rate, egg weight, fertility, hatchability, or hatchling weight over a 13-wk trial period. However, 240 mg of Mn/kg supplementation significantly increased serum Mn (P < 0.05). Manganese supplements increased the eggshell breaking strength (P < 0.05) without affecting the eggshell thickness. There was no difference in serum cholesterol and estradiol. Expression of follicle-stimulating hormone) and gonadotropin-releasing hormone-I (GnRH-I) genes was significantly elevated by 240 mg of Mn/kg (P < 0.05). Furthermore, inorganic Mn supplementation doubled GnRH-I expression compared with supplementation with the organic form (P < 0.05), although serum Mn was comparable between these 2 supplements. No obvious difference was shown in gene expression of luteinizing hormone, prolactin, GnRH-I receptor, inducible NO synthase, and dopamine receptor D1 in the pituitary as well as tyrosine hydroxylase and inducible NO synthase in the hypothalamus. This suggests that dietary Mn supplementation could improve eggshell quality in the long term. The central mechanism of nontoxic high doses of Mn suggested the transcriptional activation of GnRH-I and follicle-stimulating hormone genes. The central effect of inorganic Mn activating GnRH-I genes compared with the reduced effect by organic Mn could possibly be due to a decreased capacity of the latter passing through the blood-brain barrier.