The Super Chicken

Seventy-five years ago, it took a chicken 84 days to reach a weight of 1.3 kg. Today, a chicken can reach 3 kg in just 42 days—twice the weight in half the time. How were these “super chickens” created? It all began when farmers started crossing different chicken breeds to produce larger, meatier offspring (Figure 1A) [1]. Then they discovered that these birds needed more protein to build muscle, fats, and carbohydrates for energy, and they need more vitamins to grow properly. The chickens’ diets were carefully adjusted to include the exact nutrients they needed. Farmers also discovered that adding antibiotics to the feed helped protect the birds’ health (Figure 1B).

Antibiotics were widely used because they not only reduced gut diseases but also helped chickens grow with less feed. This is why they were called growth-promoting additives. Unlike antibiotics used to treat illness, these growth promoters were given in much smaller doses mixed into the feed every day. Over time, researchers and veterinarians noticed that some antibiotics no longer worked to treat sick chickens. The reason was that some bacteria had become resistant to antibiotics, meaning that the medicine no longer cured infected birds (Figures 1C, D).

How did this happen? Bacteria carry tiny information chips called plasmids, where they store the secrets to surviving antibiotics. The resistance information spread between bacteria and could be passed on through chicken droppings, the farm environment, cages, and even the meat sold at grocery stores. When authorities discovered this risk, many countries banned the use of antibiotics as growth promoters in chickens. It was decided that antibiotics could only be used if prescribed by a veterinarian to treat an illness. This rule is still in place today. However, after growth promoters were banned, chickens started getting more intestinal infections. So, farmers and veterinarians returned to using antibiotics—but only to treat sick birds, not to make them grow faster [2]. But what exactly did antibiotics do that helped chickens stay healthy and grow bigger?

The Magic Formula of Antibiotics

The digestive system of a chicken is made up of the beak, esophagus, crop, proventriculus, gizzard, small intestine, ceca, colon, and cloaca (Figure 2). When a chick hatches from the egg, thousands of bacteria enter its digestive system, coming from the hen, the environment, and the feed. Beneficial bacteria settle in the intestine and help the immune system work properly to defend the body. The immune system is made up of specialized cells and tissues that work together like soldiers and military bases to protect the body from infections and diseases. Beneficial bacteria help maintain order and prevent harmful bacteria from growing. If harmful bacteria do grow, the immune “soldiers” attack and eliminate them.

In broiler chickens, hatching takes place in industrial incubators that mimic a hen’s warmth. Therefore, chicks do not receive bacteria from their mother but instead acquire them from the incubator, transport boxes, and the farm environment. Some of these bacteria can also activate the immune system, but they do not always help control harmful bacteria. If there are too many harmful bacteria, the gut’s immune soldiers cannot fight them all—and this is where growth-promoting antibiotics come into play. These antibiotics were added to the feed to reduce the total number of bacteria in the gut—both beneficial and harmful. With fewer bacteria, the immune system had less work to do. This allowed the chicken to save energy and use it to grow and build muscle, which would eventually become meat [3].

Safe Solutions

Today, we know that the bacteria living in the gut are called the intestinal microbiota, and they are very important for a chicken’s health. Scientists have looked for safer ways to care for the chickens without using antibiotics. The alternative substances used are called probiotics, prebiotics, and synbiotics [4]. These feed additives help beneficial bacteria grow, reproduce, and protect the gut.

What Are Probiotics And Prebiotics?

Probiotics are beneficial bacteria added to chicken feed. Their role is to strengthen the army of bacteria already living in the gut. When probiotic bacteria reach the intestine, they begin to feed and produce an acidic substance called lactic acid. Lactic acid limits the growth of harmful bacteria, which then stop multiplying. For beneficial bacteria, however, this acidic environment is more favorable, so they multiply faster and the intestinal balance improves.

Prebiotics are sugars joined by special locks called β-glucosidic bonds, which the chicken’s digestive enzymes cannot break so they cannot use the sugars for energy. Beneficial bacteria, however, have the key to open these β-glucosidic locks. Once opened, they can obtain energy from the sugars, allowing them to reproduce, grow, and produce acids that stop the development of harmful bacteria.

The combination of prebiotics and probiotics is called synbiotics. Prebiotics serve as nutrients that feed the beneficial bacteria, and probiotics are the beneficial bacteria that use these nutrients to grow and support gut health.

The Challenges of The “Super Chicken”

Although natural feed additives help maintain a healthy digestive system in chickens, they are not the only thing that matters. For a chicken to grow up healthy, its entire environment must be well-managed. When chicks arrive at the farm, strict biosecurity measures must be followed to prevent disease. These include restricting access to only necessary people and vehicles, requiring farmers to shower before entering, and preventing contact with rodents, dogs, cats, or any animal that might bring harmful bacteria.

Inside the farm, the care continues. Warm temperatures (about 32°C) are needed during the first days. Light is adjusted to reduce stress and promote rest. The floor is covered with soft bedding like sawdust, and feed must provide essential nutrients such as proteins, carbohydrates, fats, vitamins, and minerals. High-quality diets are based on ingredients like corn and soybean oil for energy, and soybean meal for protein. If any of these elements are missing, the chicken’s gut may be affected, harmful bacteria may grow, and the bird may become sick.

Unfortunately, not all farmers can meet these requirements due to limited resources. When this happens, antibiotics are still used to treat diseases—even though their risks are known. That is why, although natural additives are a good tool, scientists continue looking for more effective options to support the growth of beneficial bacteria. The main goal of farmers is to protect the chickens’ health and welfare—and that is how they hope to raise the “super chicken” [5].

Glossary

Antibiotics: ↑ Medicines that kill or stop harmful bacteria that cause diseases. They help animals and humans recover when they are sick.

Growth Promoters: ↑ Antibiotics added at lower doses than those used for treating infections, to improve gut health and boost chicken growth.

Immune System: ↑ The body’s natural defense force, made of specialized cells that detect and fight bacteria, viruses, and other threats to keep an animal healthy.

Intestinal Microbiota: ↑ All the tiny living microbes in your intestines, many of which help digest food and keep your body healthy.

Probiotics: ↑ Good bacteria that you eat or drink to help your stomach and intestines stay healthy.

Prebiotics: ↑ Special fibers that feed the good bacteria in your intestines so they can grow.

Synbiotics: ↑ A mix of probiotics and prebiotics that work together to improve gut health.

β-glycosidic Bonds: ↑ Connections or “locks” between sugars in plant fibers. Only certain beneficial bacteria can break them to use the sugars for energy.

Conflict of Interest

The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

AI Tool Statement

The author(s) declared that generative AI was not used in the creation of this manuscript.

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