Susceptibility of Broiler Chickens to Coccidiosis When Fed Subclinical Doses of Deoxynivalenol and Fumonisins-Special Emphasis on the Immunological Response and the Mycotoxin Interaction

Abstract

Deoxynivalenol (DON) and fumonisins (FB) are the most frequently encountered mycotoxins produced by Fusarium species in livestock diets. The effect of subclinical doses of mycotoxins in chickens is largely unknown, and in particular the susceptibility of birds to pathogenic challenge when fed these fungal metabolites. Therefore, the present study reports the effects of DON and FB on chickens challenged with Eimeria spp, responsible for coccidiosis. Broilers were fed diets from hatch to day 20, containing no mycotoxins, 1.5 mg DON/kg, 20 mg FB/kg, or both toxins (12 pens/diet; 7 birds/pen). At day 14, six pens of birds per diet (half of the birds) were challenged with a 25×-recommended dose of coccidial vaccine, and all birds (challenged and unchallenged) were sampled 6 days later. As expected, performance of birds was strongly affected by the coccidial challenge. Ingestion of mycotoxins did not further affect the growth but repartitioned the rate of reduction (between the fraction due to the change in maintenance and feed efficiency), and reduced apparent nitrogen digestibility. Intestinal lesions and number of oocysts in the jejunal mucosa and feces of challenged birds were more frequent and intense in the birds fed mycotoxins than in birds fed control feed. The upregulation of cytokines (interleukin (IL) IL-1β, IL-6, IL-8 and IL-10) following coccidial infection was higher in the jejunum of birds fed mycotoxins. Further, the higher intestinal immune response was associated with a higher percentage of T lymphocytes CD4⁺CD25⁺, also called Tregs, observed in the cecal tonsils of challenged birds fed mycotoxins. Interestingly, the increase in FB biomarker of exposure (sphinganine/sphingosine ratio in serum and liver) suggested a higher absorption and bioavailability of FB in challenged birds. The interaction of DON and FB was very dependent on the endpoint assessed, with three endpoints reporting antagonism, nine additivity, and two synergism. In conclusion, subclinical doses of DON and FB showed little effects in unchallenged chickens, but seem to result in metabolic and immunologic disturbances that amplify the severity of coccidiosis.

Keywords: challenge; coccidiosis; interaction; intestinal immune response; mycotoxins.

Figure 1

Relationship between the reductions in feed intake and growth rate (Experiment 1, based on Pastorelli et al. [24]): (a) Relationship between the change in growth (∆BWG, Body Weight Gain day 14–20) and feed intake (∆FI, Feed Intake day 14–20) of chickens challenged with a coccidial vaccine. Responses are expressed as results of the challenged chickens relative to that of unchallenged chickens on control feed (in %, 11 birds/diet). The lines represent the linear model adjustments; (b) Partitioning of the reduction in the average growth rate following the challenge between the fraction due to change in maintenance requirement (i.e., not associated with a reduction in feed intake) or due to the change in feed efficiency (i.e., associated with a reduction in feed intake).

Figure 2

Lesion scoring in the gastrointestinal tract (GIT) of chickens challenged with the coccidical vaccine (Experiment 1). Each plot reports the score of individual data of 12 birds per diet. No significant differences between contaminated diets and control diet were observed in the duodenum. In the mid-jejunum, significant differences were noted in the mean lesion score (±SEM): 1.42 ± 0.40 (p = 0.029), 1.25 ± 0.43 (p = 0.084), and 0.58 ± 0.31 (p = 0.442), respectively, for DON, FB and DON + FB compared to control diet, 0.08 ± 0.08. Similarly, the mean lesion scores significantly differed in the ceca of birds: 1.33 ± 0.28 (p = 0.019), 1.33 ± 0.38 (p = 0.049), and 1.33 ± 0.36 (p = 0.041), respectively, for DON, FB and DON + FB compared to control diet, 0.42 ± 0.23.

Figure 3

Oocyst counting in the jejunal mucosa and excreta of chickens challenged with the coccidial vaccine (Experiment 1). McMaster slide was used to count the floating oocysts under microscope at 10× magnification. Values are mean ± SEM for six birds (mucosa) and six pools (excreta). Means with no common superscript are significantly different (p < 0.05).

Figure 4

Biomarker of exposure to FB, sphinganine/sphingosine ratio in the serum, liver and ileum of unchallenged and challenged chickens (Experiment 1). White and black bars represent unchallenged and challenged birds, respectively. Values are mean ± SEM for six birds. *, p ≤ 0.05; ***, p ≤ 0.001. Means with no common superscript (lower and upper case for unchallenged and challenged birds, respectively) are significantly different (p < 0.05).

Figure 5

Gene expression in the jejunum of chickens challenged with coccidial vaccine (Experiment 1). The white bar (first bar in each plot) represents the mean value of the unchallenged birds on control feed. The darker bars represent the mean value of the challenged birds on experimental diets, and expressed relative to the unchallenged control group. Values are mean ± SEM for six birds. Means with no common superscript are significantly different (p < 0.05). S, Significant and NS, Non-Significant difference between both control groups, unchallenged and challenged.

Figure 6

Experimental design: 336 birds (7 birds/pen, 12 pens/diet) were fed the experimental diets until day 20, half were orally challenged at day 14 with 25× of coccidial vaccine, and all were sampled at day 20. In parallel, 192 birds (4 birds/pen, 12 pens/diet) were fed the same experimental diets until day 20, half were orally challenged at d 14 with 25× of coccidial vaccine, and at day 20 all of the birds were kept on basal feed until day 34.