By: Dr. drh. Dahliatul Qosimah, drh, Mkes Faculty of Veterinary Medicine, Universitas Brawijaya

Imagine a farmer who has just harvested their flock. However, the harvest weight is below target, the FCR (Feed Conversion Ratio) has ballooned, and sudden mortality appeared in the third week. Upon necropsy, the chicken’s liver and heart are coated in a yellowish membrane with characteristic cheesy (caseous) signs. The diagnosis is clear: Colibacillosis.

This story is nothing new. In fact, because it occurs so frequently, colibacillosis is often regarded as an “ordinary” disease in the Indonesian poultry industry. However, research by Wibisono et al. (2018) shows that economic losses due to colibacillosis reach 13.10% of total national poultry assets—a highly significant figure.

The risk increases sharply during the rainy season. High humidity, difficult-to-dry litter, and compromised ventilation create ideal conditions for E. coli to thrive and attack. It is important to understand that not all E. coli are dangerous. Some live normally in the chicken’s gut without causing issues. However, approximately 10–15% are Avian Pathogenic E. coli (APEC), which possess virulence factors that allow them to penetrate the gut, spread to vital organs, and cause serious damage (Kathayat et al., 2021).

APEC most frequently enters through the respiratory tract. House dust containing fecal particles is inhaled by the bird, the bacteria enter the air sacs, and then spread to the heart, liver, and other organs, causing colisepticemia and rapid death. Another pathway is through contaminated hatching eggs, which produce weak DOCs (Day-Old Chicks) with inflamed navels, stunted growth, and high early mortality.

Why is Colibacillosis Called a Secondary Disease?

Colibacillosis is often called a secondary disease because APEC is rarely the primary invader. Generally, the infection is initiated by other diseases such as Infectious Bronchitis (IB) or Mycoplasma, which damage the chicken’s respiratory defenses first. This damage opens a “point of entry” for E. coli from the farm environment.

As a result, clinical symptoms like rales (snoring) can rapidly progress into severe airsacculitis, caseous lesions on the liver and heart, and mass mortality. Because they appear simultaneously, field cases are often confusing and look like a single disease, when in fact they are multiple infections: the primary disease opens the door, and colibacillosis exacerbates the impact.

DISEASES THAT FREQUENTLY “INVITE” COLIBACILLOSIS:

• Newcastle Disease (ND) — Damages the respiratory mucosa.

• Infectious Bronchitis (IB) — Main targets: upper respiratory tract and oviduct.

• Mycoplasmosis (CRD) — Chronic infection that weakens respiratory defenses.

• Gumboro/IBD — Suppresses the immune system (immunosuppression).

• Coccidiosis — Damages the intestinal mucosa, opening a pathway for E. coli into the bloodstream and deeper into the digestive system.

Rainy Season: When All Risk Factors Collide

The rainy season is the most vulnerable period for colibacillosis. High humidity makes litter difficult to dry, while ventilation often fails to exhaust moisture optimally. Wet litter is the primary trigger. When moisture content reaches 25–35%, the litter clumps and becomes an ideal breeding ground for E. coli. This condition also accelerates the release of ammonia, which damages the chicken’s respiratory tract and increases the incidence of footpad dermatitis.

Ammonia acts as a silent destroyer. Exposure to just 15 ppm triggers respiratory inflammation, while 25 ppm causes stunted growth, worsening FCR, and increased airsacculitis. This damage to the respiratory epithelium clears the way for E. coli to enter the air sacs, bloodstream, and vital organs. Ventilation during the rainy season becomes a dilemma: closed curtains keep out the rain but build up ammonia; open curtains improve circulation but wet the litter. The solution is managed partial openings on the side safe from wind-driven rain, maintaining minimum ventilation, and using exhaust fans where possible.

Figure 2. Colibacillosis Risk Factors in the Rainy Season

Antibiotics are Losing Effectiveness: A Serious Alarm

Many antibiotics historically used for colibacillosis are now losing their efficacy due to Antimicrobial Resistance (AMR). Studies in Indonesia indicate that more than 50% of broiler E. coli isolates are resistant to tetracycline and ciprofloxacin, and approximately 25% are classified as MDR (Multidrug-Resistant)—immune to three or more classes of antibiotics. The main cause is the use of antibiotics without diagnosis, without sensitivity testing, and at irrational doses and frequencies. Routine antibiotics given to healthy chickens “train” bacteria to become resistant, posing a threat not only to bird health but also to human health through the food chain.

What Should Be Done?

Colibacillosis is preventable, and prevention is far cheaper than treatment. Here are the key steps to implement:

1. Keep Litter Dry: Dry litter is the most important factor. Use highly absorbent materials (dry rice husks or wood shavings), maintain a depth of 5–10 cm, turn it routinely, immediately replace wet areas (especially around drinkers), and ensure nipple drinkers do not leak.

2. Manage Ventilation Properly: Avoid stagnant air in the house. In open houses, open curtains asymmetrically on the side safe from rain. In closed houses, ensure exhaust fans and minimum ventilation are functional. Ideal targets: Relative Humidity (RH) <70% and Ammonia <25 ppm.

3. Strengthen Biosecurity: E. coli exists in the environment, but populations can be suppressed. Disinfect and dry the house between production cycles, and control vectors such as rats, flies, cockroaches, and wild birds.

4. Timely Vaccination: Since colibacillosis is often secondary, prevent the primary diseases. Ensure ND, IB, and Mycoplasma vaccinations are on schedule. Avoid vaccinating during poor environmental conditions. APEC vaccines can be considered as a supplement.

5. Use Antibiotics Wisely: Antibiotics are not for routine prevention. If treatment is necessary, perform a sensitivity test. Non-antibiotic alternatives like probiotics, organic acids, and phytobiotics can help suppress E. coli without the risk of resistance.