In large-scale laying hen farming, everyone is highly vigilant about highly virulent infectious diseases. But there is a flock-wide subclinical problem that quietly depletes flock productivity, raises the feed-to-egg ratio, and creates respiratory risks. Many farmers have struggled with it for years without recognizing it in time—it is internal heat accumulation syndrome in laying hens.
 
　　Internal heat is not a standalone infectious disease; it is an imbalance in visceral metabolism that develops gradually through long-term accumulation. There is no large-scale acute mortality, and the symptoms are scattered and fluctuate in severity, so it is very easy to mistake the condition for ordinary enteritis or mycoplasmal respiratory disease and treat it superficially. When there is a large day–night temperature difference and ventilation is poorly managed, internal heat combined with cold stress creates the “cold enveloping fire” condition that farmers fear most. This makes management several times more difficult and causes losses to continue mounting. Today, we will explain internal heat syndrome in detail, covering recognition, pattern differentiation, contributing factors, and prevention and control principles, to help everyone inspect their houses and make targeted adjustments.
 
　　I. Quick identification during house inspections: 4 key signs to tell at a glance whether the flock has internal heat
 
　　Internal heat first appears in the external features of the head, then shows up in the droppings, respiratory tract, and egg production. Observing the flock in this order during house inspections is the most efficient approach.
 
　　1, physical signs of the face and body: the first criterion for initially assessing internal heat
 
　　The combs of healthy chickens are normally rosy and glossy. Chickens with internal heat have dry-red or purplish-red combs, with dry, rough tips and little luster. This is a typical sign that internal heat is consuming body fluids and causing stagnation of qi and blood, and is completely different from the pale combs caused by anemia. Eye symptoms: persistent redness and congestion of the conjunctiva, dry eyes, and, in some chickens, foamy discharge at the corners of the eyes. This is not simply bacterial conjunctivitis. When chickens are overheated, they frequently pant with their mouths open, drink noticeably more, and actively seek cool water. This is an instinctive response to dissipate heat and counter internal heat. A somewhat red tongue is also a typical accompanying sign of internal heat.
 
　　2, fecal signs: the key to distinguishing internal heat from ordinary enteritis
 
　　Feces are the most direct indicator of cold and heat in the internal organs. Feces associated with internal heat have two characteristic types:
 
　　Dry green droppings: a classic sign of internal heat. The droppings are formed but somewhat dry, with a layer of green bile coating the outside. The underlying cause is stagnated heat in the liver and gallbladder, with bile overflowing;
 
　　Yellowish-white, sticky droppings: highly sticky and corrosive, leaving obvious burn marks when they fall on cage wire or the ground.
 
　　Many chickens with internal heat also have diarrhea. Here is a key point for distinguishing the two: in chickens with diarrhea caused by internal heat, the area around the vent is warm and hot to the touch; with diarrhea caused by ordinary bacterial or viral enteritis, the chicken’s vent is cool. Using this point can greatly reduce misdiagnosis.
 
　　3, respiratory signs: beware of internal heat meeting cold, forming “cold enveloping fire”
 
　　Internal heat is the root cause; drafts, cooling, and temperature fluctuations are the triggers. When internal heat accumulates in a chicken for a long time, lung qi becomes obstructed. Once cold air gets in, the pores on the body surface tighten, preventing the heat inside from dissipating. When the internal and external pathogenic factors clash, chickens may shake their heads, make rattling sounds, and cough. There is one very typical feature: symptoms are mild during the day and worsen at night. During the day, chickens are more active and the air circulates well, so the rattling and coughing are less easy to hear. At night, chickens huddle together to rest, and stale air and moisture accumulate in the house, causing respiratory symptoms to flare up together. If respiratory medication is used alone without clearing the internal stagnated heat, the condition can easily become a stubborn respiratory problem that keeps recurring and is difficult to resolve.
 
　　4, egg-laying performance: internal heat brings the most direct economic losses
 
　　Internal heat first damages eggshell quality: shells become dull and grayish, without a bright luster; pigment deposition worsens and color fades; thin-shelled, broken, and misshapen eggs continue to increase. The mechanism is that internal heat damages the body's metabolism and impedes the synthesis of the eggshell protective membrane. Persistent internal heat consumes the chickens' reserves over time: egg weight increases more slowly, the laying peak shortens, nutrient absorption becomes disordered, and feed conversion efficiency declines. The flock's immunity continues to weaken, scattered weak chickens persist, and mortality and culling rise slowly and slightly. This is a chronic, ongoing drain; over time, the difference in returns becomes very noticeable.
 
　　II. Feeding, demeanor, and anatomical references to help confirm internal heat
 
　　Heat-stressed chickens are irritable and restless, startle easily, dislike stuffy conditions, and avoid enclosed, high-temperature areas. Their feed intake fluctuates, gastrointestinal digestion is disrupted, the feed-to-egg ratio gradually rises, and feed costs increase. Typical findings on dissection: the liver is congested, enlarged, and yellow, with pinpoint or patchy hemorrhages, indicating liver stagnation and heat stasis; edema of the glandular stomach papillae is characteristic of dry heat damaging the digestive tract mucosa and impairing organ function.
 
　　Three: Six major causes—understanding how internal heat develops
 
　　Internal heat is rarely caused by a single factor. It usually results from multiple overlapping stresses. The two most common root causes on farms are the accumulation of mycotoxins and stuffy, poorly ventilated poultry houses. Other contributing factors include:
 
　　Feeding large amounts of new-crop corn: resistant starch and a high metabolic burden can easily place stress on liver and bile metabolism;
 
High dietary nutrient levels: Long-term feeding of high-protein, high-energy diets overloads metabolism in the internal organs;
 
Lingering effects of heat stress: Prolonged exposure to high temperatures causes heat to build up in the body and remain unprocessed;
 
Immune stress: Vaccine stimulation causes temporary stagnation of qi and blood heat in the body;
 
Management shortcomings: Imbalanced ventilation practices prevent stale, humid air from being expelled.
 
　　Many poultry farmers focus only on medication-based treatment and fail to address the underlying causes. Internal heat then keeps recurring, naturally making treatment much less effective.
 
　　Four. Distinguish excess heat from deficiency heat; proper treatment based on the pattern avoids taking the wrong approach
 
　　Internal heat is divided into excess heat and deficiency heat, which require completely different treatment approaches. Using the same medication indiscriminately is less effective and can easily harm the chickens’ constitution.
 
　　The excess-heat type (acute internal heat) occurs mostly during the high temperatures of midsummer or in the early stages of an infectious disease, and is an acute outbreak. The comb is bright red and hot to the touch, water consumption surges, droppings are characteristically dry and green, and the flock is overexcited and restless, with strong stress responses. Rapid heat-clearing and pathogen-dispersing treatment is suitable.
 
　　The deficient-heat type (chronic latent heat, more common at peak laying) is a subclinical condition that is most easily overlooked. There is no acute illness or mass mortality; the combs are dry, rough, and dark red, egg shells remain dull for a long time, and minor problems recur repeatedly. The flock is physically weak and has low immunity. The key is not to aggressively use cold-natured remedies to purge fire, but to nourish yin, clear latent heat, and strengthen the foundation, while also attending to the care of the internal organs.
 
　　Five. Prevention and control approach: prevention is better than treatment; identify early and begin care early
 
　　Core principles for internal heat syndrome: first focus on management, then consider care; tailor measures to the pattern.
 
　　Conduct routine daily poultry-house inspections, making the combs, droppings, egg shells, and nighttime respiratory tract the main points of observation. Compare against the indicators to detect problems early.
 
Optimize ventilation management to prevent stuffy housing and drafts from occurring together, reduce temperature-difference stress, and avoid cold wrapped in heat at the source;
 
Control raw material quality and prevent mold. Use new corn in a well-balanced way, and avoid overloading birds with high-nutrition diets over the long term;
 
Adjust treatment according to whether the heat is excess or deficient: for excess heat, focus on clearing heat and dispersing fire; for deficient heat in peak-production flocks, focus on nourishing yin, relieving stagnation, and strengthening the body's foundation. Do not indiscriminately use large amounts of cooling medicines, which can damage the spleen and stomach;
 
Stabilize intestinal and liver function. Keep the liver and gallbladder flowing freely and the intestines healthy so that the pathways for metabolizing internal heat remain unobstructed and accumulation is reduced.
 
Here’s a practical saying from the field to help everyone remember the signs in daily practice:
 
When hens have internal heat, their combs are dry and red; they drink much more and pass dry, green droppings;
 
Eggshells turn dull, breathing becomes labored, and mold in a poorly ventilated coop is the root cause.
 
Internal heat is invisible, but it steadily eats away at our poultry-farming profits. Raising healthy laying hens means not only preventing serious diseases, but also paying attention to this chronic subclinical problem. Understand internal heat, learn to identify its signs, and intervene earlier through management. This helps keep the flock stable, reduce recurring respiratory problems, and maintain a steady peak in egg production—naturally taking farming returns to the next level.