Necrotic enteritis in poultry

Original article available in Nutrinews Magazine

Necrotic enteritis is an enterotoxemia that usually affects chickens between 2 and 5 weeks of age and can cause high mortalities, up to 50%, when it occurs acutely.

However, its subclinical form, which negatively affects nutrient absorption, worsening on average, is common:

12% in weight gain
nearly 11% conversion rate

This leads to necrotic enteritis, mainly the subclinical form, causing severe economic damage inbroiler production, estimated at more than 1770 million euros per year globally (Avian Pathol. 2011; 40: 341-347; World Poult. 2000, 16: 42-43; Avian Dis. 2010: 54, 1237-1240).

The causative agent is the spore-forming Gram-positive anaerobic bacteria Clostridium perfringens, basically types A and C, capable of producing toxins (α and NetB) that induce damage in the epithelium of the small intestine (jejunum and ileum) and liver, mainly (J Appl Poult Res. 2016; 44: 359-369).

It is known that Clostridium perfringens is a ubiquitous microorganism, present even in the intestine of healthy birds. Therefore, a triggering factor is usually necessary for it to induce the lesions characteristic of necrotic enteritis.

These triggers often converge in altered gut microbiota composition or damage to the intestinal mucosa, including:

coccidiosis – especially Eimeria acervulina and Eimeria maxima-.
mycotoxicosis
salmonellosis
ascaridiosis
elevated levels of certain ingredients in the diet, factors that promote slowed intestinal transit or bacterial overgrowth, among others (Anim Nutr. 2015; 1: 1-11).

Prior to its prohibition, the use of antibiotics in feed for prophylactic purposes prevented necrotic enteritis.

In fact, in countries with a ban on the use of growth-promoting antibiotics, the incidence of necrotic enteritis has increased (Anim Nutr. 2015; 1: 1-11).

Therefore, in our post-antibiotic era, other strategies must be resorted to, such as:

improve immune response
reduce pathogen load
and/or use feed additives, such as certain organic acids (OAs) or plant extracts with antimicrobial effect (Anim Nutr. 2015; 1: 1-11).

Effects of the combination of short-chain organic acids and phytogenic substances against necrotic enteritis.

One of the aspects that explain the efficacy against necrotic enteritis of specific combinations of short-chain OCs with phytogenic substances (SF) is the antimicrobial effect they exert on Clostridium perfringens, among other pathogenic bacteria (Table 1).

This is because the bacterial wall composition consists of 90-95% peptidoglycans, which allows the passage into the cellular interior of hydrophobic molecules, such as non-dissociated forms of AO and certain SF (Pathogens. 2015; 4: 137-56).The combination of AO + SF exhibits broad-spectrum antimicrobial efficacy, effective against Gram-positive bacteria such as Clostridium perfringens, the causative agent of necrotic enteritis in chickens.

Method of antimicrobial action of OCs and FSs

Non-dissociated forms of the AO (Advances in Pork Production. 2005; 16: 169). can:

penetrate the bacterial wall
destructuring the cytoplasmic membrane
and dissociate inside it, reducing the pH
and, together with the anion generated, alter metabolic functions, leading to the death of the bacteria.

In the case of phytogenic (SF) molecules, the antimicrobial effects would be caused (Pharm. 2013, 6: 1451-1474) by:

damage to the bacterial membrane,
the inhibition of enzymes of the bacterial energy metabolism
denaturation of certain proteins

Several authors describe an additive or synergistic effect of the AO-SF combination at the level of antimicrobial effect. This could be explained by different mechanisms.
On the one hand, the blocking of certain bacterial enzymes and the change of fatty acid profiles that induce the destabilization of the bacterial membrane, thus favoring the passage of OCs and making them more susceptible to an acidic environment.
Also, low pH could increase the hydrophobicity of SFs, thus favoring their passage through the bacterial wall and membrane (Pathogens. 2015; 4: 137-56).

The antimicrobial effects of OCs begin in the feed itself and then predominate in the animal’s crop, proventriculus and gizzard.

In contrast, in the case of SFs, these persist in later sections of the gastrointestinal tract, which seems to contribute to the benefits of the AO+SF combination (Anim Prod Sci. 2017; 57: 821-827).

Other positive effects of OCs and SF

In addition to this antimicrobial efficacy against Clostridium perfringens, both OCs and SFs can produce positive effects on factors that contribute to the occurrence of necrotic enteritis or its consequences.

Phytogenic substances (SF) … In addition they can:

Preserve and stimulate the absorption function of the gastrointestinal tract.
Improve epithelial morphology, increasing the length of intestinal villi and, therefore, the absorption surface.
Increasing the secretion of endogenous digestive enzymes.
Regulating the intestinal microbiota
Modulate immune responses (by regulating the expression of proinflammatory markers).
Antioxidant effects
and even, as in the case of cinnamaldehyde, act against Eimeria (Anim Prod Sci. 2017; 57: 821-827; Vet. Parasitol. 2011, 181: 97-105).

Organic acids (AO) … In addition, as described in Advances in Pork Production. 2005; 16: 169, they can stimulate:

the development of the gastrointestinal mucosa
epithelial growth, absorptive capacity, epithelial growth, absorptive capacity, and
and electrolyte transport (greater absorption of ions and water), helping to prevent diarrhea, among other effects.

Experimental test of AO-SF combinations

These multi-day effects of specific AO-SF combinations would explain the improvements in productive parameters obtained with AO + SF combination* in the trial carried out at IRTA(Institut de Recerca i Tecnologia Agroalimentàries. Tarragona, Spain).

Test animals: 372 male Ross 308 chickens (12 chickens/pen), fed a diet based on wheat, barley and soybean.
Treatments:

Distributed in the following treatments (10-11 replicates/treatment) depending on whether they were experimentally infected with Eimeria spp. and Clostridium perfringens, as a model of necrotic enteritis:

Inoculated animals were administered live attenuated oocysts of Eimeria acervulina, E. maxima, E. mitis and E. tenella on day 9.

On days 15, 16 and 17, inocula of10⁷ -10⁸ CFU of C. perfringens obtained from farms affected by necrotic enteritis were administered.

Duration: 35 days
Parameters assessed: productive parameters and mortality were evaluated.

Results

The inclusion of the combination* of AO + SF at 2.5 kg/t feed significantly improved live weight, average daily gain, average daily intake and feed conversion (days 0-35) compared to the inoculated control group, restoring the parameters and mortality to normal levels (fig. 1 and 2; table 2).

Conclusions:

Specific combinations of organic acids and phytogenic substances can improve the health status of animals infected with Eimeria spp. and Clostridium perfringens, and are effective in preventing necrotic enteritis in broilers.
In conditions of infection with Eimeria spp. and Clostridium perfringens, specific combinations of organic acids and phytogenic substances are able to improve production parameters, which can be restored to normal levels without infection.
Organic acids and phytogenic substances can act synergistically or additively, increasing their antimicrobial activity and/or beneficial effects on gastrointestinal health and physiology.
Specific combinations of organic acids and phytogenic substances constitute an alternative to antibiotic growth promoters and a useful tool for reducing the use of therapeutic antibiotics.

The combination* of AO + SF tested in this paper was ENASSENCE