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

Energy- Total Digestible Nutrients (TDN) 

• TDN is a common standard for measuring energy in animal feed in the U.S. 
• It includes digestible protein, crude fiber, nitrogen-free extract (NFE), and fat, multiplied by 2.25. 
• Forages typically have a TDN ranging from 45% to 65%, while grains range from 65% to 85%. 
• However, TDN doesn't account for all energy losses during digestion and doesn't accurately reflect energy differences between forages and concentrates.

Digestible Energy 

• Digestible energy is determined by subtracting energy lost in feces from the gross energy intake of a feed. 
• This measure is obtained through digestion trials and provides insights similar to TDN.

Metabolizable Energy 

• Metabolizable energy is calculated by subtracting energy lost in urine and combustible gases from digestible energy. Urine losses are higher with roughages compared to concentrates. 
• The amount of combustible gases is measured using a respiration calorimeter.

Net Energy 

• Net energy is obtained by subtracting the heat increment from metabolizable energy. 
• Heat increment is the increase in heat production during feed consumption and digestion in the gastrointestinal tract. 
• Net energy reflects the true value of feed for productive purposes like growth, reproduction, maintenance, and production of milk or fat. 
• It is expressed in therms or megacalories and provides a more accurate measure of a feed's value for productive purposes.

By using these different measures of energy, animal nutritionists can better understand the energy content of feeds and formulate balanced diets to meet the energy requirements of animals effectively.