The "White Dragon" horse that jumped into the river to save people died. Why do people always say "an ox is made of iron, but a horse is made of paper"?

Produced by: Science Popularization China

Author: Liu Wenjin

Producer: China Science Expo

At 9 p.m. on February 11, the white horse "Bailong" who had bravely followed his owner into the water to save people seven days ago died.

Let's review the news at that time:

At 1:50 pm on February 4, in the Hanjiang River section of Xiantao City, Hubei Province, the wind was biting cold and the water temperature was only 6 degrees Celsius. A man was struggling in the river, his life in danger. Relatives on the shore shouted anxiously. At the critical moment, Yilibai jumped into the river on his white horse "Bailong" and rushed straight into the icy river to rescue him. In the end, Yilibai, his friends Su Shaogao and Liu Hangzhou worked together with the "Bailong" horse to rescue the man to shore.

"White Dragon" horse rescue scene

(Photo source: Jiupai News)

The average lifespan of a horse is usually between 25 and 35 years old. Bailong was only 7 years old when he died, which was the prime of his life.

According to the consultation, Bai Long died of sudden intestinal strangulation. Intestinal strangulation can be simply understood as the intestine twisting like a towel, blocking blood flow or damaging intestinal tissue. This can occur in multiple parts of the intestine, especially in curved or narrowed areas. The disease develops quickly, lasts for a short period of time, and has a high mortality rate.

Many experts have worked together to treat

(Photo source: CCTV News)

The horse's owner, Yilibai Dosongbieke, said that on February 10, a bystander fed Bailong without permission. Therefore, many netizens suspected that Bailong's death was caused by private feeding.

In fact, there are many causes of intestinal strangulation: parasitic infection, intestinal inflammation, electrolyte (salt) imbalance, diet, daily activities, medication and other environmental changes may all lead to the disease.

Considering that Bai Long had experienced intense exercise, sudden changes in temperature after diving into the water to save people, and had a high fever the next day, it is difficult to determine the cause of his death without further examination.

How terrible is colic for horses?

In addition to intestinal strangulation, other intestinal obstructions, intussusception, gastric dilatation, gastric rupture, inguinal hernia, etc. are also common in equine animals such as horses, mules and donkeys. These types of diseases are collectively called colic. Colic is one of the main causes of death in horses worldwide. In some areas, colic may even cause up to 1/4 of the mortality rate in horses.

Why is the horse's stomach so fragile? This is mainly related to the following factors:

1. Complex gastrointestinal structure: The horse's digestive tract is long and complex, with many twists and turns, which increases the risk of blockage, displacement, and tortuosity.

2. Abdominal movement: Many gastrointestinal structures float freely in the horse's abdominal cavity, making them easily shifted or twisted during normal movement. As we all know, horses are very fast animals. Some thoroughbred racehorses can carry a person and run 1,000 meters in one minute. This speed also accelerates the fragility of the gastrointestinal tract.

Donkeys have a lower incidence of colic than horses, which is also related to the fact that donkeys are slower than horses.

Horse digestive system anatomy

(Image source: Atlas of Horse Anatomy)

3. Hindgut fermentation: Horses are hindgut fermenters, which means they rely on a diverse microbiome in their hindgut to ferment their fiber feeds. This process produces gas, and any disruption (such as a sudden dietary change) can lead to increased gas accumulation, inflammation, or motility problems.

4. Basically unable to vomit: Because of the one-way structure of the esophagus and the small stomach capacity, horses cannot vomit except in extremely rare cases. This means that they cannot relieve the pressure caused by gas or obstruction, and even a small digestive problem may threaten the horse's life.

Horses may vomit water when unwell, but vomiting other contents is extremely rare

(Image source: Internet)

Why is it “an iron ox and a paper horse”?

From the perspective of evolution, the reason why horses' stomachs are fragile is essentially the result of a balance between pros and cons.

The "ancestor of all horses", the Eohippus, was small in size and mainly lived in the forest environment during the Eocene period more than 50 million years ago. It mainly fed on young leaves, fruits and other foods that were nutritious and easy to digest, so the intestines of early horses were shorter and simpler in structure.

Evolutionary tree of horses

(Image source: Ernst Mayr on Evolution)

As the climate became drier and grasslands expanded (about 25 million years ago), the size of horses gradually increased. In order to adapt to the predation pressure in the grassland environment, horses evolved the ability to run at high speeds. Their bodies became more streamlined, their abdominal space was compressed, and their intestines became more tightly arranged.

Beautiful and smooth modern horse shape

(Photo credit: The Incredible Horse)

At the same time, the horse's teeth evolved high-crowned teeth to chew silica-rich herbs, and the digestive system also shifted to a hindgut fermentation mode (extended cecum and colon structures) to efficiently extract energy from fiber.

Such evolution obviously comes at a price. The horse's gastrointestinal structure has a small space and heavy tasks. At the same time, the overall structure still retains some primitive characteristics (such as a relatively short small intestine), resulting in low fiber fermentation efficiency and low stability of the microbial community, and limited response to changes in external pressure.

Compared with horses, cows' gastrointestinal functions are obviously stronger (horses belong to the order Perissodactyla and cows belong to the order Even-toed Undulate, and they are not closely related).

The ancestors of cattle (such as primitive ruminants about 30 million years ago) also lived in open grassland ecosystems. When faced with natural selection pressure, the large size of cattle (adult cattle can weigh up to 500-1000 kg) can provide sufficient evolutionary space for their digestive system:

The aurochs of the Miocene (23 million years ago) could weigh more than 1 ton.

(Photo source: Chengjiang Fossil Site Museum)

They have chosen a strategy of extreme resource utilization, evolving a unique four-chamber stomach and rumination behavior. With this strategy and a stable microbial community (the mass of microorganisms in the cattle's forestomach can account for more than 50% of the total stomach weight), cattle not only have a strong buffering capacity against external disturbances (such as feed changes), but also can efficiently decompose the cellulose in the plants they eat.

Multi-chambered stomach structure of cattle

(Image source: Bing)

These evolutionary traits make cattle one of the most successful cellulose converters on land, with a digestive system that is far more resistant to interference than monogastric and hindgut fermenters, including, yes, horses.

Therefore, for farmers, there is a well-known saying that "cows are made of iron, but horses are made of paper." Although it is a bit exaggerated, it is indeed much more difficult to take care of horses than cows and sheep. Special attention should be paid to temperature control, feeding mode, and external environmental pressure.

After all, the fragile stomach and intestines of horses are a "historical debt" that they have to bear during the evolutionary process.

References:

[1] Huang Ruiyu, (1984), A case of vomiting in a military horse,

[2] Editorial Board of Exploration at Your Fingertips. Incredible Horse, Chemical Industry Press, 2015

[3] ByAllison J. Stewart, (2024), Intestinal Disorders Other than Colic in Horses, https://www.merckvetmanual.com/horse-owners/digestive-disorders-of-horses/intestinal-disorders-other-than-colic-in-horses#Salmonellosis_v3217916

[4] Sara Rice, MSc., (2024), Top 6 Gastrointestinal Conditions in Horses: Colic & Other Digestive Disorders, https://madbarn.com/gastrointestinal-conditions-in-horses/