Blood is a fluid containing different types of cells circulated by the heart to the entire body via the circulatory system’s network of arteries, capillaries, and veins. It ferries oxygen and nutrients to the cells while also removing waste such as carbon dioxide.

Animals are both warm and cold-blooded, with either an open or closed circulatory system. A closed circulatory system is found only in a few invertebrates and vertebrates. 

• Insects, crustaceans, molluscs, etc., have an open circulatory system.
• Birds, mammals, fish, reptiles, amphibians, and some invertebrates are examples of closed circulatory systems.

Red blood cells, white blood cells, plasma, and platelets are the key blood constituents in animals with a closed circulatory system.

Some facts about animal blood constituents

• The size of red blood cells varies from animal to animal. In mammals, the red blood cells lack nuclei and organelles, but they have four respiratory pigments – Hemerythrin, Haemoglobin, Haemocyanin, and Chlorocruorin. These are present outside animals’ cells with a closed circulatory system. 
• There are numerous different blood groups in animal species. As human blood has a red colour, animals can have red, green, blue, or pink pigment in their blood.

What are blood constituents in animals?

If a sample of blood from an animal is placed in a tube and left to rest for a few hours, it will settle into three different layers:

• The yellow top layer is plasma,
• white blood cells are in the centre, and 
• red blood cells are at the bottom.

The important blood constituents in animals are:

Red blood cells

Also known as Erythrocytes, red blood cell value falls between 30-40% in animals. Animals in high altitudes have higher PCV [ Packed cell volume] or red blood cells than those in low altitudes. 

White blood cells

White blood cells, also known as Leucocytes, are lower than red blood cells. The ratio of red blood cells to white blood cells is 1000:1. White blood cells protect the body of an animal against infections.

Plasma 

Plasma is made up of 91% water with numerous substances dissolved, for example – Electrolytes, Proteins, Nutrients, Gases, and Hormones.

Platelets 

Platelets are an essential component of animal blood, whose function is to clot the blood on getting injured.

Serum

The serum is a straw-coloured fluid left behind when the blood clots.

George Gulliver summarised animal blood constituent research in 1875 by drawing red blood cells from over 80 species of vertebrates, highlighting the similarities and differences in their structures, size, and shape.

As per scientific research, the conclusion was like the following:

• All vertebrates and several invertebrates, except some fish species, have haemoglobin.
• Some marine invertebrates, such as Magelona, have Hemerythrin, a violet-pink colour on being oxygenated.
• Animals with an open circulatory system have hemocyanin, which turns blue when oxygenated.
• Chlorocruorin, found in Annelids and marine Polychaetes, is red when oxygenated and green when deoxygenated.
• In most species, white blood cells and platelets are similar, although the proportion of each cell type may differ.
• Some animals like fish have four different forms of white blood cells.
• Cattle, horses, cats, and dogs have A and B antigens in their blood cells.

Important functions of blood constituents in animals

Following are the critical functions of blood carried out inside animal bodies:

• Blood transports the gases such as oxygen and nutrients to the body’s cells and removes waste products like carbon dioxide.
• The blood maintains normal body temperature.
• Blood helps animals in maintaining acidity levels or pH. Inside the body of an animal, blood balances the acid-base equilibrium.
• Blood provides immunity with the help of white blood cells to fight against infections and diseases.
• Enzymes and hormones are regulated and transported by the blood constituents in animals.

Blood types in animals

Antigens on the surface of erythrocytes are used to define blood types. Humans have A, B, and O group of blood types, but other animal species have numerous blood types; some of these are given below:

Dogs

Eight major blood groups are found in dogs, referred to as DEA [dog erythrocyte antigen] 1 to 8.

Cats

Only one blood group has been identified in cats, AB system: A, B, and AB groups.

Horses

Horses have roughly 30 blood groups, with just eight of them being the main ones.

Only seven of these eight groups are internationally recognised A, C, D, K, P, Q, and U.

Cattle

A, B, C, F, J, L, M, R, S, T, and Z are the major 11 blood groups in cattle, with the B group having more than 60 different antigens.

Sheep

The B system, like cattle, is highly polymorphic. A, B, C, D, M, R, and X are the seven blood groups found in sheep.

Goat

Very similar to sheep, there are five significant systems of blood found in goats, A, B, C, M, and J.

Conclusion

Humans and animals both have blood in their bodies which is necessary for delivering nutrients and oxygen to the body cells and the removal of waste materials. The important blood constituents of animals are red blood cells, white blood cells, plasma, and platelets. 

While humans have haemoglobin in their blood, animals have four different respiratory pigments present in their blood. Furthermore, distinct forms of blood-borne antigens are found in various types of animal blood.

The elements of each type make the main difference between human and animal blood.