Effects of Feeding Blends of Grains Naturally Contaminated with ...

Effects of Feeding Blends of Grains Naturally Contaminated with Fusarium Mycotoxins on Performance, Metabolism, Hematology, and Immunocompetence of Ducklings S. R. Chowdhury,* T. K. Smith,*,1 H. J. Boermans,† A. E. Sefton,‡ R. Downey,§ and B. Woodward¶ *Department of Animal and Poultry Science, †Department of Biomedical Sciences, University of Guelph, Guelph, Ontario, Canada N1G 2W1; ‡Alltech Biotechnology Center, Nicholasville, Kentucky 40356; §King Cole Duck Ltd., Aurora, Ontairo, Canada L4G 3H3; and ¶Department of Human Biology and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada N1G 2W1 ABSTRACT Experiments were conducted to determine the effects of feeding grains naturally contaminated with Fusarium mycotoxins on performance, metabolism, hematology, and immune competence of ducklings. Four hundred sixty-four 1-d-old White Pekin male ducklings were fed starter (0 to 2 wk), grower (3 to 4 wk), and finisher (5 to 6 wk) diets formulated with uncontaminated grains, a low level of contaminated grains, a high level of contaminated grains, or the higher level of contaminated grains + 0.2% polymeric glucomannan mycotoxin adsorbent. Body weight gains, feed consumption, and feed efficiency were not affected by diet. However, consumption of contaminated grains decreased plasma calcium concentrations after 2 wk and plasma uric acid concentrations at the 4-wk assessment point. Mean corpuscular hemoglobin concentrations and hematocrit decreased when ducks were fed contaminated grains for 4 or 6 wk, respectively. In contrast, total numbers of white blood cells and lym-

phocytes increased transiently in birds fed contaminated grains for 4 wk. The antibody response to sheep red blood cells (CD4+ T cell dependent) and the cell-mediated response to phytohemagglutinin-P (also CD4+ T cell dependent) were not affected by diet, but consumption of contaminated grains for 6 wk decreased the duration of peak cell-mediated response to dinitrochlorobenzene (CD8+ T cell dependent) assessed in a skin test. Feeding grains naturally contaminated with Fusarium mycotoxins, even at levels widely regarded as high, exerted only minor adverse effects on plasma chemistry and hematology of ducklings, and production parameters were unaffected in this avian species. Mycotoxin-contaminated feeds may, however, render these animals susceptible to infectious agents such as viruses against which the CD8+ T cell provides necessary defence. Glucomannan mycotoxin adsorbent was not effective in preventing alterations caused by Fusarium mycotoxins.

(Key words: Fusarium mycotoxin, duck performance, plasma chemistry, hematology, immune competence) 2005 Poultry Science 84:1179–1185

Mycotoxins are secondary metabolites of filamentous fungi. Mycotoxicoses are a worldwide problem causing significant financial losses to animal industries (Hussein and Brasel, 2001). Fusarium trichothecenes are cytotoxic (Schiefer and Beasley, 1989) and cause oral lesions and pathology to the liver, kidneys, nervous system (Feuerstein et al., 1989), and immune system (Taylor et al., 1989). These pathologies may occur, in part, because trichothecenes inhibit protein synthesis (Feinberg and McLaughlin, 1989) and interfere with nutrient absorption (Hunder et al., 1991).

Consumption of grains naturally contaminated with Fusarium mycotoxins did not alter the antibody-mediated immune response of turkeys to SRBC, but the cell-mediated immune response to dinitrochlorobenzene (DNCB) was depressed (S. R. Chowdhury, T. K. Smith, H. J. Boermans, and W. B. Woodward, 2005, unpublished data). Exposure of mice to 10 mg zearalenone (ZEN)/kg of diet for 2 wk decreased resistance to listeriosis. Resistance to Listeria monocytogene, moreover, was reduced to a greater extent by coadministration of deoxynivalenol (DON) with ZEN even though indices of humoral and cell-mediated immune competence were not affected (Pestka et al., 1987).

2005 Poultry Science Association, Inc. Received for publication January 21, 2005. Accepted for publication May 2, 2005. 1 To whom correspondence should be uoguelph.ca.

Abbreviation Key: CHS = contact hypersensitivity; DNCB = dinitrochlorobenzene; DON = deoxynivalenol; GMA = glucomannan mycotoxin adsorbent; MCHC = mean corpuscular hemoglobin concentrations; ZEN = zearalenone.

INTRODUCTION

addressed:

tsmith@

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Aflatoxicosis is well documented in ducks due to the extreme adverse effects of aflatoxin on health and performance of ducks, whereas few reports describe the effect of Fusarium mycotoxins. A diet containing 1.2 mg of DON/kg, 4.5 mg of fumonisin/kg, and 0.01 mg of aflatoxin B1 /kg resulted in 50% mortality to White Pekin ducklings after 7 d of feeding because of total feed refusal (Davis et al., 1994). In apparent contrast, Boston et al. (1996) reported no adverse effects on feed intake, body weight gain, organ weights, or plasma chemistry when adult Mallard ducks were fed naturally contaminated wheat containing 5.8 mg of DON/kg for 2 wk. It has been suggested that consumption of grains containing low concentrations of mycotoxins may not alter production parameters but that such concentrations may impair the resistance of waterfowl to infectious diseases (Smith et al., 1990). No information is available on immunocompetence of ducks fed Fusarium mycotoxins. The current study was conducted, therefore, to determine the effects of feeding grains naturally contaminated with a combination of Fusarium mycotoxins on performance, metabolism, hematology, and immune competence of ducklings. Glucomannan mycotoxin adsorbent (GMA) has proven beneficial in preventing mycotoxicoses arising from a combination of mycotoxins in turkeys (Chowdhury and Smith, 2004, unpublished data), broiler chickens (Swamy et al., 2002), and laying hens (Chowdhury and Smith, 2004). An additional objective of the investigation, therefore, was to investigate whether any adverse effects observed in ducklings could be prevented by dietary supplementation with GMA.

MATERIALS AND METHODS Experimental Design A total of 464, male, 1-d-old White Pekin ducklings were individually weighed, wing-banded, and distributed randomly into groups of 29 birds per floor pen. In turn, 4 pens were randomly assigned to each of 4 diets such that each diet was fed to 116 birds. Ducklings were initially maintained at 31°C, and the temperature was lowered by 2°C per week to reach 21°C by the end of wk 5. This temperature was maintained for the final week of the study. Ducklings were fed corn-, wheat-, and soybean meal-based starter (0 to 2 wk), grower (3 to 4 wk), and finisher (5 to 6 wk) diets formulated with uncontaminated grains, a low level of contaminated grains, a higher level of contaminated grains, or the higher level of contaminated grains + 0.2% GMA. Within each of the 3 periods (starter, grower, and finisher) diets were isoenergetic and isonitrogenous, and nutrient concentrations met or exceeded minimal requirements according to the National

2 Veterinary Diagnostic Laboratory, North Dakota State University, Fargo, ND. 3 Becton Dickinson, Franklin Lakes, NJ. 4 Roche Diagnostics, Division of Hoffman-La Roche Limited, Montreal, QC, Canada.

Research Council (1994). The mycotoxin-contaminated diets were formulated to the nutrient specifications of the uncontaminated diet by replacing 50 or 100% of the uncontaminated corn and wheat with corn and wheat naturally contaminated with Fusarium mycotoxin. Feed and water were provided ad libitum. Representative feed samples were taken at the beginning of each phase of feeding for nutrient and mycotoxin analyses. Dry matter, crude protein, calcium, and phosphorus contents of the diets were analyzed according to the Association of Official Analytical Chemists (1980). The project was approved by the University of Guelph Animal Care Committee and met the guidelines of the Canadian Council on Animal Care.

Analysis of Dietary Mycotoxins Dietary contents of DON, 3-acetyl-DON, 15-acetylDON, nivalenol, T-2 toxin, iso T-2 toxin, acetyl-T-2 toxin, HT-2 toxin, T-2 triol, T-2 tetraol, fusarenone-X, diacetoxyscirpenol, scirpentriol, 15-acetoxyscirpentriol, neosolaniol, ZEN, zearalenol, aflatoxin, and fumonisin were determined by gas chromatography and mass spectrometry2 (Raymond et al., 2003). Fusaric acid was determined by the HPLC method of Matsui and Watanabe (1988) as modified by Smith and Sousadias (1993) and confirmed by Porter et al. (1995).

Experimental Parameters Measured Performance Ducklings were weighed individually once per week, and feed consumption for each pen was also measured weekly during the 6-wk experimental period. Biweekly and cumulative weight gain and feed consumption were determined, and gain-to-feed ratios were calculated using these measured values. Feed consumption and gain-tofeed ratios were adjusted for mortality when required. Among the 116 birds per diet only one bird per treatment died. The day dead bird was removed from the pen was counted. The amount of feed each bird consumed per day in that particular period was calculated. This amount of feed was added to calculate feed consumption for the pen. At the end of d 42, three birds per pen were killed by cervical dislocation, and the livers and spleens were excised and weighed.

Plasma Chemistry At the end of d 14, 28 and 42, blood samples (1 mL/ bird, 3 birds/pen) for plasma chemistry and hematology were collected from the jugular vein using vacutainer tubes containing sodium heparin.3 Plasma concentrations of total protein, albumin, globulins, glucose, uric acid, cholesterol, bilirubin, calcium, and phosphorus and activities of amylase, lipase, lactate dehydrogenase, aspartate aminotransferase, γ-glutamyltransferase, and creatine kinase were determined using a Hitachi 911 autoanalyzer.4

FUSARIUM MYCOTOXINS IN DUCKLINGS

Hematology Hematocrit was determined with a Micro-Capillary Reader5 after a 5-min centrifugation.6 Hemoglobin was measured as cyanomethemoglobin with a Hemoglobinometer7 after the red blood cells were lysed. In addition, mean corpuscular hemoglobin concentrations (MCHC) were calculated as MCHC = hemoglobin/hematocrit. Differential white blood cell counts were performed using blood smears stained with modified Wright’s stain using the Hematek Stain Pak.8 One hundred white blood cells were examined per bird using a Nikon microscope9 set at 400× magnification, and heterophils, lymphocytes, monocytes, eosinophils, and basophils were identified. In addition, total counts of heterophils and eosinophils were made with a Neubauer hemacytometer10 and a Nikon microscope9 set at 100× magnification. For this purpose the cells were stained with phyloxine B in aqueous propylene glycol.11 Numbers of lymphocytes, monocytes, and basophils were determined by calculation.

Antibody Response to SRBC At the end of d 14, immediately following the collection of preimmune sera, 3 birds per pen were injected intravenously with 1 mL of 10% SRBC12 in PBS. Primary immune serum was collected subsequently on d 21 and 28. SRBC were readministered as described above on d 28, and secondary immune serum was collected subsequently on d 35 and 42. Serum IgM and IgG antibody titers specific to SRBC were measured according to Temple et al. (1995) with some modifications. Detection antibodies used in the assay13 were horse radish peroxidase conjugated goat anti-duck IgM (µ-chain specific, 0.1 µg/mL) or goat antiduck IgG (Fc-fragment specific, 0.4 µg/mL). The antibody titer was defined as the highest dilution of the test serum whose absorbance was greater than the average absorbance plus 3 standard deviations of 8 wells without serum.

Contact Hypersensitivity Response to DNCB The method of Prescott et al. (1982) was applied with minor modifications to 3 birds per pen on d 25. Fifty microliters of 90% dimethylsulfoxide in deionized water14

5

Damon Division, IEC, Needham Heights, MA. Hettich Haematokrit, Diamed Lab Supplies Inc. Mississauga, ON, Canada. 7 Coulter Electronics, Mississauga, ON, Canada. 8 Bayer Inc., Toronto, ON, Canada. 9 Nikon Instruments, Tokyo, Japan. 10 Electron Microscopy Sciences, Hatfield, PA. 11 Unopette, Becton Dickinson, Franklin Lakes, NJ. 12 Cleveland Scientific, Bath, OH. 13 Bethyl Laboratories, Montgomery, TX. 14 Fisher Scientific Ltd., Nepean, ON, Canada. 15 Sigma Chemical Co., St. Louis, MO. 16 Mitutoya Corp., Tokyo, Japan. 6

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was applied on an area of wing skin previously cleaned with 70% ethyl alcohol in deionized water. Ten minutes later, birds were sensitized with 50 µL of 5% DNCB15 dissolved in acetone. The same procedure was subsequently conducted every 48 h for 6 d. Two weeks after the first sensitization, the right webfoot of each sensitized birds, as well as of 3 unsensitized birds per pen, was challenged by application of 50 µL of 0.4% DNCB dissolved in a 4:1 mixture of acetone and olive oil. In addition, 50 µL of acetone: olive oil was applied to the left webfoot as a control. The thickness of the webfoot was measured before the challenge as well as at 24, 48, and 72 h after challenge using a constant-tension dial micrometer. The average value from 3 measurements was calculated for each webfoot, and the response resulting from the challenge was calculated as the percentage of thickness increase in the right webfoot minus the percentage of thickness increase in the left webfoot. Finally, the lymphocyte-mediated contact hypersensitivity (CHS) response was calculated by subtracting the response to challenge in unsensitized birds (n = 12 per diet) from the response in sensitized birds.

The CHS Response to Phytohemagglutinin-P The CHS response to phytohemagglutinin-P, a lectin from Phaseolus vulgaris,15 was measured using the methodology of Corrier (1990). On d 35, the webfeet of 3 birds from each pen were cleaned of litter and debris using 70% ethyl alcohol. The ducklings were then injected intradermally between the third and fourth digits of the right webfoot with 100 µg of phytohemagglutinin-P dissolved in 100 µL of endotoxin-free sterile physiological saline. The left webfoot of each bird was similarly injected with 100 µL of sterile physiological saline to serve as a control. The thickness of each webfoot was measured 24 h after injection and was calculated as the average of 3 measurements taken with a constant-tension dial micrometer.16 The CHS response was calculated as the percentage of thickness increase in the right webfoot minus the percentage of thickness increase in the left webfoot.

Statistical Analyses The experiment was conducted according to a completely randomized design with subsampling (Kuehl, 1994). Data were tested for homogeneity of variance using the Levene test. Data were then analyzed by analysis of covariance (initial body weights used as the covariate for body weight gains and final body weights used as the covariate for relative organ weights) or by analysis of variance using the general linear model procedure of SAS software (SAS Institute, 2000). Orthogonal polynomial contrasts were used to search for responses to diets (Kuehl, 1994). The efficacy of supplemental GMA was determined by using a contrast between diets containing the same level of contaminated grains with and without GMA. Statements of statistical significance were based

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TABLE 1. Mycotoxin concentrations (µg/g) of experimental diets Dietary group Starter (0–2 wk) Control Low4 High5 High+6 Grower (3–4 wk) Control Low High High+ Finisher (5–6 wk) Control Low High High+

TABLE 2. Effect of feeding grains naturally contaminated with Fusarium mycotoxins on feed consumption, body weight gain, and feed efficiency1

Mycotoxin DON1

15-acetyl-DON

ZEA2

0.6 7.3 14 13.3

ND3 0.4 0.8 0.8

ND 0.6 1.3 1.1

0.7 7.8 16.3 17.5

0.2 0.5 0.8 1.0

ND 0.6 1.3 1.3

0.5 6.3 18.6 17.7

ND 0.4 1.0 0.8

ND 0.5 1.2 0.9

1

Deoxynivalenol. Zearalenone. 3 Below the limit of detection. 4 Fifty percent of the control corn and wheat was replaced by contaminated corn and wheat. 5 One hundred percent of the control corn and wheat was replaced by contaminated corn and wheat. 6 One hundred percent of the control corn and wheat was replaced by contaminated corn and wheat + glucomannan mycotoxin adsorbent. 2

on P < 0.05. For each index assesses, the pen was taken as the statistical unit so that data from individual birds of the same pen were pooled.

RESULTS Dietary Mycotoxin Concentrations Dietary concentrations of DON, 15-acetyl-DON, and ZEN are given in Table 1. Mycotoxins other than these were below the limits of detection which were 0.02 mg of aflatoxin/kg, 2 mg of fumonisin/kg, 0.77 mg of fusaric acid/kg, and 0.2 mg/kg for the remainder of the mycotoxins analyzed.

Production Parameters Consumption of grains naturally contaminated with Fusarium mycotoxins did not alter feed consumption, feed efficiency, or body weight gains in the starter, grower, or finisher phases (Table 2). Relative liver and spleen weights (body weights used as covariate) were also not affected by diet (data not shown).

Plasma Chemistry Consumption of increasing levels of contaminated grains decreased plasma calcium concentrations linearly (P < 0.05) after 2 wk but exerted no effect thereafter (Table 3). Consumption of increasing levels of contaminated grains for 4 wk decreased plasma uric acid concentrations according to a quadratic dose response (P < 0.05). Supplementation of the diet containing a high level of contami-

Diet Feed consumption (g/bird) Control Low2 High3 High+4 Pooled SE Linear Quadratic High vs. high + Body weight gain (g/bird) Control Low High High+ Pooled SE Linear Quadratic High vs. high + Feed efficiency (body weight gain/feed intake) Control Low High High+ Pooled SE Linear Quadratic High vs. high +

0–2 wk

3–4 wk

5–6 wk

867 857 869 876 7 NS5 NS NS

2,693 2,656 2,642 2,698 36 NS NS NS

3,532 3,553 3,419 3,556 60 NS NS NS

590 589 601 610 5 NS NS NS

1,214 1,210 1,215 1,258 13 NS NS NS

1,085 1,015 1,026 1,079 15 NS NS NS

0.68 0.69 0.69 0.70 0.002 NS NS NS

0.45 0.45 0.46 0.47 0.002 NS NS NS

0.31 0.29 0.30 0.30 0.005 NS NS NS

1 Values are least square means; for each diet and phase, n = 4 pens for feed consumption and feed efficiency, whereas n = 4 pens and 29 birds per pen for body weight gain. 2 Fifty percent of the control corn and wheat was replaced by contaminated corn and wheat. 3 One hundred percent of the control corn and wheat was replaced by contaminated corn and wheat. 4 One hundred percent of the control corn and wheat was replaced by contaminated corn and wheat + mycotoxin adsorbent (GMA). 5 P > 0.05.

nated grains with GMA prevented neither the transient early reduction in plasma calcium concentration nor the later (also transient) reduction in uric acid concentrations.

Hematology Consumption of grains naturally contaminated with Fusarium mycotoxins decreased MCHC quadratically, but total numbers of white blood cells and lymphocytes increased linearly (P < 0.05) only after 4 wk (Table 4). No effect of diet was observed on these parameters in the early or in the later period of the study. Hematocrit values decreased linearly (P < 0.05) after 6 wk of consumption of contaminated grains but not before. Supplemental GMA was without impact on the influences of Fusarium mycotoxins on blood cell indices.

Immunology There was no effect of diet on primary or secondary antibody titers of IgM or IgG specific for SRBC (P > 0.05; data not shown). The CHS response to DNCB decreased linearly with dietary mycotoxin level when assessed 48

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FUSARIUM MYCOTOXINS IN DUCKLINGS TABLE 3. Effect of feeding grains naturally contaminated with Fusarium mycotoxins on plasma calcium and uric acid concentrations1

TABLE 4. Effect of feeding grains naturally contaminated with Fusarium mycotoxins on hematology1 Diet

Diet Calcium (mmol/L) Control Low2 High3 High+4 Pooled SE Linear Quadratic High vs. high + Uric acid (µmol/L) Control Low High High+ Pooled SE Linear Quadratic High vs. high +

Wk 2

Wk 4

Wk 6

3.15 3.13 3.09 3.08 0.03 0.05 NS NS

3.08 3.04 3.05 3.06 0.03 NS5 NS NS

3.03 3.01 3.00 2.82 0.08 NS NS NS

582 519 581 473 40 NS NS NS

463 367 410 371 26 NS 0.03 NS

532 456 468 445 33 NS NS NS

1

Values are least square means; for each diet and phase, n = 4 pens and 3 birds per pen. 2 Fifty percent of the control corn and wheat was replaced by contaminated corn and wheat. 3 One hundred percent of the control corn and wheat was replaced by contaminated corn and wheat. 4 One hundred percent of the control corn and wheat was replaced by contaminated corn and wheat + mycotoxin adsorbent (GMA). 5 P > 0.05.

h after challenge, and this phenomenon was not influenced by GMA (Table 5). There was no effect of diet on the CHS response to phytohemagglutinin-P (Table 5).

DISCUSSION The DON was detected in all control diets, and 15acetyl-DON was detected in the control diet of the grower phase, thereby indicating that diets containing apparently uncontaminated corn and wheat, nevertheless, contained detectable amounts of mycotoxins. DON concentrations were similar in the diets containing contaminated grains with and without GMA. Two other mycotoxins, 15-acetylDON and ZEN, were also detected as minor components in the diets and, therefore, might have contributed to the mycotoxicoses noted in this investigation. It has been reported that adult ducks are resistant to dietary levels of DON below 6 mg/kg arising from naturally contaminated wheat (Boston et al., 1996). In agreement with this previous study, and extending this knowledge to younger birds, the present investigation showed that production parameters of ducklings were resistant to a diet containing 18.6 mg of DON/kg, 1.0 mg of 15-acetyl-DON/kg, and 1.2 mg of ZEN/kg, levels widely regarded as high in practical poultry diets. In contrast, consumption of grains naturally contaminated with comparatively low levels of Fusarium mycotoxins impaired performance of turkey poults (S. R. Chowdhury and T. K. Smith, 2004, unpublished data), broiler chickens (Swamy et al., 2002), and laying hens (Chowdhury and Smith, 2004). It appears that ducks are a particularly resis-

Hematocrit (L/L) Control Low2 High3 High+4 Pooled SE Linear Quadratic High vs. high + MCHC (g/L)6 Control Low High High+ Pooled SE Linear Quadratic High vs. high + Total white blood cells (109/L) Control Low High High+ Pooled SE Linear Quadratic High vs. high + Lymphocytes (109/L) Control Low High High+ Pooled SE Linear Quadratic High vs. high +

Wk 2 0.35 0.35 0.35 0.36 0.005 NS5 NS NS

Wk 4 0.35 0.35 0.34 0.35 0.005 NS NS NS

Wk 6 0.39 0.36 0.33 0.34 0.002 0.05 NS NS

334 329 334 324 2.89 NS NS NS

363 337 346 355 3.75 NS 0.03 NS

335 337 334 337 4.91 NS NS NS

16.38 13.68 14.32 15.32 1.71 NS NS NS

13.1 17.4 17.6 15.6 1.41 0.03 NS NS

15.91 16.40 16.22 17.48 2.15 NS NS NS

5.08 6.56 4.18 4.77 0.64 NS NS NS

3.89 5.52 5.86 4.24 0.84 0.05 NS NS

4.77 5.93 6.37 6.88 1.17 NS NS NS

1 Values are least square means; for each diet and phase, n = 4 pens and 3 birds per pen. 2 Fifty percent of the control corn and wheat was replaced by contaminated corn and wheat. 3 One hundred percent of the control corn and wheat was replaced by contaminated corn and wheat. 4 One hundred percent of the control corn and wheat was replaced by contaminated corn and wheat + mycotoxin adsorbent (GMA). 5 P > 0.05. 6 Mean corpuscular hemoglobin concentration (MCHC) = (hemoglobin/hematocrit).

tant avian species where effects of Fusarium mycotoxins on production parameters are concerned. The transient minor reduction in plasma uric acid concentrations in birds fed low concentrations of Fusarium mycotoxins in the current study does not correlate in an obvious way with the resistance of production parameters. Likewise, we can provide no reason for the transient reduction in plasma calcium concentrations, but this phenomenon has also been observed in turkeys (S. R. Chowdhury and T. K. Smith, 2004, unpublished data) and laying hens (Chowdhury and Smith, 2004) and, therefore, appears to be reproducible in various avian species. Although a mycotoxin-induced reduction in hematocrit was observed, the levels remained within the normal range for ducks (Campbell, 2000). This phenomenon has been reported in several other avian species, namely laying hens (S. R. Chowdhury, T. K. Smith, H. J. Boermans,

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TABLE 5. Effect of feeding grains naturally contaminated with Fusarium mycotoxins on cell mediated immunity1 Increase in webfoot thickness (%) DNCB2

PHA-P3

Diet

24 h

48 h

72 h

24 h

Control Low4 High5 High+6 Pooled SE Linear Quadratic High vs. high +

14.10 15.49 13.93 12.50 2.71 NS7 NS NS

13.03 7.95 5.25 4.18 2.35 0.01 NS NS

7.26 5.95 5.61 4.33 2.36 NS NS NS

53 58 54 63 6 NS NS NS

1

Values are least square means; for each diet and time point, n = 4 pens and 3 birds per pen. 2 1-Chloro-2, 4-dinitrobenzene. 3 Phytohemagglutinin-P. 4 Fifty percent of the control corn and wheat was replaced by contaminated corn and wheat. 5 One hundred percent of the control corn and wheat was replaced by contaminated corn and wheat. 6 One hundred percent of the control corn and wheat was replaced by contaminated corn and wheat + mycotoxin adsorbent (GMA). 7 P > 0.05.

and B. Woodward, 2004, unpublished data), turkey poults (S. R. Chowdhury, T. K. Smith, H. J. Boermans, and B. Woodward, 2005, unpublished data), and growing chicks (Kubena et al., 1985). It appears that the hematocrit is resistant to Fusarium mycotoxins in birds. The reason for the transient elevation in peripheral white blood cell counts when birds consumed contaminated grains is not clear. In contrast, reduction in blood cell counts was observed in laying hens fed mycotoxin-contaminated grains (S. R. Chowdhury, T. K. Smith, H. J. Boermans, and B. Woodward, 2004, unpublished data). The current study also aimed to investigate mycotoxininduced alteration in assays of antibody-mediated and cell-mediated immune competence. The present study extends previous investigation in which grains naturally contaminated with Fusarium mycotoxins failed to alter the antibody response to SRBC in laying hens (S. R. Chowdhury, T. K. Smith, H. J. Boermans, and B. Woodward, 2004, unpublished data), broilers (Swamy et al., 2004) or turkey poults (S. R. Chowdhury, T. K. Smith, H. J. Boermans, and B. Woodward, 2005, unpublished data). Thus, it appears that antibody mediated immune competence of avian species is resistant to Fusarium mycotoxins. By contrast, mycotoxin-contaminated diets appeared to alter the kinetics of the cell-mediated response to DNCB by inducing an early resolution to the reaction without affecting its peak. In this context it is noteworthy that the anti-SRBC antibody response depends on CD4+T cell help (Goldsby et al., 2000), whereas the anti-DNCB response is mediated by CD8+ T cells (Okazaki et al., 2002) with CD4+ T cells primarily exerting suppression (Gunnes et al., 2004). Further, the cell-mediated response to phytohemagglutinin-P, another reaction requiring CD4+ T-cell help without involvement of CD8+ T cells (Karmanska et al., 1996) was also refractory to Fusarium mycotoxins.

Consumption of mycotoxin-contaminated feeds, therefore, may render ducklings particularly susceptible to infections (e.g., by viruses) against which CD8+ T cells are particularly important. A similar conclusion was reached in a recent study of turkey poults (S. R. Chowdhury, T. K. Smith, H. J. Boermans, and B. Woodward, 2005, unpublished data) and, thus, may apply generally at least to avian species. Other environmental insults along with these mycotoxin-induced effects may further aggravate adverse effects. It was concluded that consumption of grains naturally contaminated with Fusarium mycotoxins, even at levels widely regarded as high, exerts only minor, mostly transient adverse effects on plasma chemistry and hematology of ducklings. Production parameters were essentially unaffected, but the birds in the current study were not raised under commercial conditions. The feeding of mycotoxin-contaminated feeds to ducklings is not, therefore, recommended because resistance to some types of infectious agents, notably viruses, may be compromised. GMA was not effective in preventing the alterations caused by Fusarium mycotoxins under the condition of this investigation.

ACKNOWLEDGMENTS Financial support for this study was provided by the Ontario Ministry of Agriculture and Food and Alltech Inc, Nicholasville, KY. The statistical advice of Margaret Quinton (Department of Animal and Poultry Science, University of Guelph) is gratefully acknowledged.

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