Metabolism and Energy Requirements | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Metabolism and Nutrient Utilization in Animals

Importance of Nutrients from Plants:

Food derived primarily from plants provides essential nutrients to animals for various purposes:

• Body maintenance for repairing worn-out tissues
• Growth for increasing size and weight
• Production of offspring
• Energy required for milk, meat, eggs, and work

Enhanced Feeding in Pregnant Animals:

• Pregnant animals, particularly in later stages of pregnancy, require increased feeding to support the growing fetus.

Importance of Metabolism: Carbohydrates, proteins, and fats in the diet contain energy that needs to undergo metabolism to be utilized by the animal:

• Nutrients must be broken down through digestion to be absorbed by the intestinal wall
• Metabolism occurs at various sites throughout the animal's body

Metabolizable Energy

The energy released through metabolism is known as metabolizable energy, which is used for:

• Body maintenance
• Production of milk, meat, eggs, and work

Metabolism and Energy Utilization in Animals

• The nutrients such as carbohydrates, proteins, and fats are transformed into a substrate pool through the process of digestion.
• This substrate pool contains the digestible energy of each nutrient, which is then converted into active kinetic energy during metabolism.
• Metabolism uses some of this energy, resulting in what is known as metabolizable energy.

Anabolism and Catabolism:

• Anabolism is a process that builds body proteins and fats, supporting the production of milk, eggs, meat, wool, and work.
• Catabolism, on the other hand, breaks down body proteins and fats back into the nutrient pool.

Energy Utilization in Animals: 

• Net energy is the balance left after energy is used for anabolism and catabolism, which is utilized for maintenance and production processes in animals.

Factors Influencing Energy Requirements

• Energy needs of animals are determined by maintenance and production requirements, which can include growth, milk or egg production, and work.
• Recommended nutrient allowances are set based on minimum requirements for physiological functions, with safety factors considered to accommodate individual differences and feed variations.

Maintenance and Production Requirements:

• Maintenance requirements are established through feeding trials and fasting catabolism studies, considering the energy needed for resting and physical activity.
• Production requirements vary based on the level of feed intake and milk production, with adjustments needed to account for nutrient digestibility changes.

Reproduction and Growth Requirements:

• Energy and protein needs during pregnancy increase as gestation progresses, with additional nutrients required in the last trimester.
• Nutrient requirements for growth depend on the breed and stage of development, with specific recommendations for different lactation stages.

Energy Requirements for Maintenance

The energy needed for maintaining the basic functions of the body in animals is known as maintenance energy requirements. Let's delve into the specifics of energy requirements for maintenance in different scenarios:

Dry Animals:

• Dry animals have relatively low energy requirements for maintenance, typically falling between 61 to 104 kcal/w0.75.
• This range signifies the amount of energy needed for basic bodily functions in animals that are not producing milk.
• For example, a dry cow with no milk production would fall within this lower range of energy requirements.

Lactating Cows:

• In contrast, lactating cows have higher maintenance energy requirements, ranging from 113 to 116 kcal/w0.75.
• Due to the increased basal metabolic rate during lactation, the energy needed to maintain bodily functions is higher in cows that are producing milk.
• For instance, a lactating cow expends more energy for activities like milk production, leading to the higher maintenance requirement.

Understanding these distinctions in energy requirements is crucial for designing appropriate diets and ensuring the well-being of animals in different physiological states.

Energy Requirements for Production

• In practical feeding, various factors such as the intake level, the ratio of concentrate to roughage, and the quality of roughage influence energy requirements.
• The physical form of the ration, such as grinding fineness or pelleting, also affects energy needs.

Milk:

• The gross energy content of milk is commonly used to determine the energy requirement for milk production.
• This energy requirement is typically represented in terms of metabolizable energy needed to produce milk.
• Scientists have established standard tables for energy requirements in milk production, ranging from 1039 to 1230 kcal per kg of 4% fat corrected milk.

Meat:

• For a calf weighing 203 kg, the energy requirement is set at 11.0 Mcal, while 10 Mcal is deemed adequate for a heifer.

Work:

• Research on the energy needs of working animals is limited.
• Existing reports suggest energy requirements ranging from 14.4 Mcal to 20.8 Mcal based on the animal's weight, with heavier animals needing more energy.

Egg:

• Satisfactory egg production is achieved when layers are fed diets containing 18% protein with energy at 2850 kcal ME/kg.