Starving for nutrients: anorexia during infection with parasites in broilers is affected by diet composition

James Taylor,Panagiotis Sakkas,Ilias Kyriazakis

doi:10.1016/j.psj.2021.101535

James Taylor, Panagiotis Sakkas + Show 1 more

Open Access

https://doi.org/10.1016/j.psj.2021.101535

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Abstract

In 2 experiments, we investigated whether diet composition plays a role in pathogen-induced anorexia, the voluntary reduction in ADFI during infection in broilers. We hypothesized that either energy or CP dietary content could influence the extent of anorexia in Ross 308 broilers and infection outcomes with Eimeria maxima. From d 13 of age, half of the birds were infected, and half were uninfected. ADFI was measured daily, and BW every 3 d until d 29. Oocyst excretion was measured daily from d 17 to 23. The impact of parasitism on the small intestine was assessed on d 19 and 25. In Experiment 1, 336 birds were offered diets progressively diluted with lignocellulose, starting from a diet with 3,105 (kcal ME/kg) and 20% CP. There was a significant interaction between infection and diet on ADFI during the acute stage of infection (d 17 to 21): for control birds diet dilution decreased ADFI and consequently reduced energy and CP intake. For infected birds, diet dilution increased ADFI, leading to the same energy and CP intake across diets. Oocyst excretion and villi length to crypt depth ratio (VCR) were constant across infected treatments. In Experiment 2, 432 birds were offered diets with constant ME (3,105 kcal/kg), but different CP contents (24, 20, 26, and 12%). Infection significantly reduced ADFI. Although there was no interaction between infection and diet on ADFI, there was an interaction on CP intake during the acute stage of infection. Infected birds on the 20% CP diet achieved the same CP intake as uninfected birds. There were no differences in the VCR and ADG of the infected birds on 24, 20 and 16% CP treatments, but birds on 12% had the lowest ADG and excreted more oocysts. We suggest that during infection, birds target a nutrient resource intake, which appears to be beneficial for infection outcomes, while at the same time they avoid excess protein intake. We conclude that different mechanisms regulate ADFI in infected and uninfected birds.

Highlights

A voluntary reduction in the feed intake of animals and humans is considered an ‘unavoidable’ characteristic of most infections (Adelman et al, 2009; Hite et al, 2019; Laurenson et al, 2011)
The ADFI of the infected birds was significantly reduced during the per-patent and acute stages of infection (P < 0.001), compared to the uninfected birds, and the daily energy and CP intakes of the infected birds were significantly reduced during all stages of infection (Table 3, P < 0.001)
Whilst there were no significant differences in the resource intakes of the infected birds, the resource intakes of the uninfected birds were affected by diet composition; both daily energy and CP intakes decreased as diet was progressively diluted with Arbocel

Summary

Introduction

A voluntary reduction in the feed intake of animals and humans is considered an ‘unavoidable’ characteristic of most infections (Adelman et al, 2009; Hite et al, 2019; Laurenson et al, 2011). We address whether pathogen-induced anorexia is sensitive to either dietary energy or CP supply We test this by progressively diluting the nutrient dense diet with a protein-free ingredient (starch); whilst such a dilution maintains the energy content of the diets, it results in diets of different CP contents. In both experiments we assess the consequences of diet composition on the outcomes of the infection, i.e. the extent of the damage caused by the parasite, the number of parasites excreted by the host, and the rate of recovery. Understanding which nutrient resources are targeted by infected hosts and the consequences of this on the outcomes of the infection, will have implications on how hosts should be fed during the critical stages of an infection

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