As the growing period in poultry production becomes progressively shorter and feed efficiency improves, health care, nutrition, and sanitation become more demanding every day. Thus, optimal feed conversion based on an adequate absorption and metabolism of nutrients formulated and supplied in the diet is a daily challenge in commercial poultry.  Intestinal health is a term that encompasses a multidisciplinary approach from an adequate nutrient ratio, quality, and safety to a systemic balance between the processes of digestion, absorption, metabolism, and immunity, without leaving aside the interaction with the microbiome, the ability to control pathogens, generate symbiosis, competition and overcome the damage caused by anti-nutritional factors. However, one of the enteric problems with the greatest economic repercussion due to its impact on intestinal integrity and health is the “Rapid Transit Syndrome (RTS)”, a multifactorial pathology with multiple implications in its diagnosis, control, and prevention.

Importance of gastrointestinal tract (git) health

The intestine is a complex organ involved in digestion, absorption, and immune activities in birds. In the post-hatching period, early access to nutrients and water stimulates the activity of the gastrointestinal tract and digestive organs in birds (Choct M., et al.,2009), even the segments of the GIT and digestive organs increase in size and weight faster in relation to body weight than other organs and tissues. In each of the intestinal segments, a high immune activity can be distinguished, showing a greater number of immune cells in the enteric tissue than in other organs, which account for 70% of the systemic immunity (Smith A.L., et al., 2022). It also involves the concept of a whole microbiome present in the intestine that acts under complementary mechanisms to reinforce immune, digestive and absorptive processes.

Thus, understanding the interactions between the microbiome, immune cells, and the processes of absorption and digestion contributes to mitigate the incidence of rapid transit syndrome and other enteric pathologies based on the application of preventive mechanisms in feed and drinking water.

Gastrointestinal motility

The feed passage rate through the GIT is influenced by the consistency and the granulometry of the feed, as well as the water content and the amount of feed consumed. Tests performed to determine the passage rate with the use of contrast media report an estimated time from 2.5 to 5 hours after feed consumption for this contrast media (barium) to be excreted through the feces, simulating the passage time of the ingested feed (Whittow, G.C. 2000).

The contraction of the gizzard is influenced by the physiological status of the animal, the type of feed and the size of the grain; a prolonged fasting state produces irregular activity of the gastrointestinal muscles, however, the peristaltic movements start from the esophagus and extend through the crop, proventriculus and gizzard, with peristaltic waves in intervals of 1/minute. Unlike the muscular stomach or gizzard in which rhythmic and regular contractions are reported every 20 to 30 seconds, the time the feed remains in the proventriculus is shorter and its digestion depends on the secretions of gastric glands and the activation of zymogens.

Finally, at an intestinal level, peristaltic and segmental movements take place every 5.6 to 6.3 seconds, influenced by a combination of mechanical, neural, and humoral factors. However, there are multiple factors that can generate susceptibility to changes in intestinal motility and an alteration of the feed passage rate, for example, the presence of non-amylaceous polysaccharides (NAP) increases the viscosity at intestinal level, modifies the ionic exchange and hydration state affecting the passage rate, as well as the absorption of some organic compounds by adhering to the feed and limiting the digestion process (Alba D.P., 2013). Even oxidative stress due to the presence of peroxides in the feed alters homeostasis states and motility at the intestinal level leading to inflammatory processes in the mucosa, an increase in fermentation with an unregulated immune response associated to excessive production of reactive oxygen species and intestinal dysbiosis.

Rapid transit syndrome: a multifactorial problem

There are numerous exogenous factors that affect intestinal motility and transit, and feed digestion in broilers; the main ones are fasting, some drugs, stress, diet composition, sanitary plans, anti-nutritional factors, or enteric pathogens. Intestinal health should include concepts related to the macro and microstructure of the intestine, since the “rapid transit syndrome” is associated with macroscopic findings such as the presence of undigested feed, feces with detached gut mucosa, the lack of pigmentation, poor uniformity and deterioration of productive performance; or microscopic changes in the intestinal epithelium that cannot be observed macroscopically but have great relevance in the clinical presentation of this syndrome, such as findings compatible with intestinal malabsorption processes due to the destruction of intestinal villi or alteration of their morphometric parameters, inflammatory processes with polymorphonuclear cell infiltration, cellular hyperplasia or diarrhea due to the alteration of the homeostatic balance and hemorrhagic processes in the lamina propria.

The presence of anti-nutritional factors or, simply, the qualitative or quantitative difference in the protein, lipid, and carbohydrate content compared with the animal’s requirements, as well as the influence of additives involved in the composition of the diet, are the main mechanisms that modify feed transit conditions.

From the first week of age, findings compatible with “Rapid transit syndrome”, intestinal dysbiosis, and homeostatic imbalance may be evidenced, favoring the onset of the clinical presentation of multiple enteric pathologies; however, when the feeding stage changes from starter to finisher at approximately day 21 ± 2, the incidence increases. In some cases, it also increases between days 28 and 35 of age due to metabolic, physiological, or environmental stress.

At the necropsy, it is possible to evidence changes compatible with proventriculitis (10%), thickening of the corneal layer of the gizzard (30%), vasculitis (70%), intestinal flaccidity (30%), thickening of the intestinal wall (80%), abnormal intestinal contents (80%), nephritis (60%) or, in some cases where no macroscopic lesions are evidenced, differential diagnoses should be ruled out and microscopic analysis through histopathology should be performed.

Alterations associated with deficient pigmentation, even when increasing the inclusion of natural pigments, and the lack of uniformity are some findings related to chronic RTS in birds over 21 days of age. Morbility is high in contrast to mortality; however, in chronic phases the predisposition to enteritis is generated by invasive infectious agents that are the cause of a greater susceptibility and an increase of mortality rates.

Numerous alternatives have been used for the treatment and control of clinical signs associated with rapid transit such as the use of exogenous enzymes supplied to improve digestibility in response to the presence of non-amylaceous polysaccharides that modify the viscosity of the intestinal content, or even phytates. However, an optimal effect of these enzymes depends on the quality and quantity of the feed, the microbiome, the age of the birds and the supplied antibacterial agents. Likewise, prebiotics as non-digestible feed ingredients that promote the development of saprophytic bacteria are considered an alternative for the control of intestinal dysbiosis whose efficacy depends on their use, type of prebiotic, inclusion level, and sanitary status. Finally, the mechanisms of action of probiotics have been widely evaluated under the principles of maintaining adequate counts of saprophytic bacteria, competitive exclusion, and modulation of the immune system, taking into account that the effectiveness of probiotic supplementation depends on factors such as the bacterial species and strain, as well as the age of the birds and type of inclusion.

The use of Thalassiosira and Actinoptychus diatoms has become relevant for the control of the rapid transit syndrome. These are algae exoskeletons with a unique cell wall made of hydrated silicon dioxide that slows down the intestinal transit speed so that feed remains for a longer time in the intestines, which increases the contact with digestive enzymes and intestinal microvilli, favoring the digestion processes. Even a reduction of water at an intestinal level is reported due to the formation of hydrogen bonds between silicates (SiO₄) and hydroxyl groups (OH^–), the former being a product of the chemical dissociation of water molecules (H₂O), which induces a greater release of hydrogen protons (H⁺) with the consequent acidification of the intestinal environment and favors saprophytic bacteria and the activity of some endogenous enzymes.

In the year 2021, a research study carried out at Universidad Cientifica Del Sur – Peru (UCSUR), conducted by Dr. Connie Gallardo and an entire team of professionals, had the aim to evaluate the inclusion of a product in broilers under experimental conditions based on activated diatomaceous earth developed by Biovet S.A. and marketed as Alquerfeed Diatom.

For the experimental design, 440 broilers were distributed into 4 treatments with 5 replicates each and 22 birds per replicate. There were two groups of males and two groups of females, each sex with a control group (standard diet) and a treated group (with Alquerfeed Diatom).

The results of the trial indicated that the treated groups obtained longer transit times, with a slowdown of 16 minutes, which was associated with an 8% reduction in litter moisture and an improvement in nutrient digestibility parameters with an average increase of 4.25% in protein digestibility and 3.14% in ash digestibility. This was related to a higher carcass yield, associated with a higher percentage of breast yield. Regarding weight and feed conversion rate, the groups that received the activated diatoms weighted an average of 92 more grams per bird and improved the feed conversion by 3.78%. Besides, the same groups showed a significant decrease in mortality (p<0.001) from the second week of life and a better final flock uniformity (p<0.001).  (Figure 5).

Conclusions

Rapid transit syndrome has become very relevant due to the economic impact it has in the industry. Undigested food, wet feces, and mucosal detachment are clinical signs evidenced in this syndrome; however, the pathophysiology is non-specific and can also be related to infectious diseases associated with different diagnoses. Because of its multifactorial etiology, it requires the evaluation of predisposing factors and the implementation of prevention and control measures, as well as the supply of additives intended to regulate the intestinal epithelium, favoring the integrity of the tissues and the regulation of local and systemic immunity. The inclusion of activated diatoms of the genera Thalassiosira and Actinoptychus in the feed as natural and inert additives that are not absorbed by the animal has been widely evaluated by studying digestibility coefficients, transit speed, and productive parameters. Results proved that they decrease the intestinal transit speed in birds so that feed remains for a longer time in the gastrointestinal tract and allows a higher nutrient absorption rate and the activity of endogenous enzymes, which improve performance parameters.

References

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