Introduction:
The animal that is commonly used for carrying loads is the donkey. Donkeys have been used as pack animals for centuries due to their strength, endurance, and ability to navigate difficult terrains. They are known for their sure-footedness and ability to carry heavy loads over long distances.

Reasons why donkeys are used for carrying loads:
1. Strength: Donkeys are strong animals with the ability to carry heavy loads. They have a sturdy build and are capable of carrying up to 20% of their body weight.

2. Endurance: Donkeys have high endurance levels, which allows them to travel long distances without getting tired easily. They are able to walk for several hours at a steady pace, making them ideal for journeys that require carrying loads.

3. Adaptability: Donkeys are adaptable to different types of terrains, including rocky and uneven surfaces. Their hooves are well-suited for such terrains, providing them with stability and preventing injuries.

4. Low maintenance: Donkeys are known for their hardiness and ability to survive in harsh conditions. They require less food and water compared to other pack animals, making them a cost-effective choice for carrying loads.

5. Intelligence: Donkeys are intelligent animals with a strong sense of self-preservation. They are cautious and can navigate difficult paths while carrying loads without endangering themselves or the cargo.

6. Gentle nature: Donkeys are generally gentle and docile animals, making them easier to handle and work with. They are less likely to become aggressive or cause harm to their handlers.

7. Cost-effective: Donkeys are relatively inexpensive to acquire and maintain compared to other pack animals like horses or mules. Their low cost makes them accessible to a wide range of people who require load-carrying animals.

Conclusion:
In conclusion, the donkey is the animal commonly used for carrying loads due to its strength, endurance, adaptability, low maintenance requirements, intelligence, gentle nature, and cost-effectiveness. They have been a reliable means of transportation for humans for centuries and continue to be used in various parts of the world for this purpose.