Physiological phases in livestock production


The science of livestock production divides itself into several different physiological phases.Every animal should be fed so that the nutritive requirements of each physiological phase of production with which it is involved are met.

The physiological phases  

  • Maintenance
  • Growth
  • Pregnancy
  • Milk Production
  • Work
  • Wool production


  • Maintaining an animal in a state of well-being or good health from day to day,makes no growth, develops no fetus or yields no product. While formulating rations, the maintenance nutrient requirements are satisfied first and the requirements for other purposes are in addition to maintenance. On an average, about one-half of all feed fed to livestock goes for maintenance.
    The requirements for maintenance are as follows:
    • Energy for the vital functions: heart beat, respiration, body temperature and for voluntary activity and other vital functions.
    • Protein for the repair of body tissues.
    • Minerals to replace mineral losses.
    • All of the vitamins are essential for maintenance.
    • Water is required for essentially all body functions.


  • Increase in muscle, bone, organs, and connective tissue. Growth is essential for an animal to produce meat or to attain mature body weight.The daily growth rate of animals increases up to puberty and then gradually declines.The nutritive requirements for growth are in addition to those listed above for maintenance. 
  • The primary nutrients required for growth:
    • Protein: The dry matter of muscle and connective tissue, and to a considerable degree, also that of bone, primarily is protein. Hence, protein is one of the major nutritive requirements of growth. Protein for growth must be of good quality-that is, it must contain the proper proportions and amounts of essential amino acids at the tissue level.
    • Energy in the form of net energy must be provided to meet this need in addition to that in the protein of tissue. Also, a certain amount of additional energy is used by the body for growth.
    • Minerals: Since bone formation is a primary activity of growth and since bone is high in calcium and phosphorus content, these two minerals are very essential for growth. Other minerals are involved in the digestion and utilization of other nutrients needed for growth.
    • Vitamins: Certain vitamins function in various metabolic processes related to nutrient utilization for growth
      Water: Fat-free muscle tissue is about 75% to 80% water. 

Milk Production

  • Milk is produced and secreted by the mammary glands. Nutrients for milk production are carried by the blood to the mammary glands. The nutrients are removed from the blood by the mammary glands, converted into milk, and secreted into the udder more or less throughout the day.
  • Nutrients for milk production must come from the feed, either directly or indirectly via body reserves of nutrients, which come originally from the animal's feed.
  • The peak milk production is reached during 4-8 weeks after lactation starts and the animals also lose body weight during early lactation since their appetite is low and they may not take sufficient feed to meet the nutrient requirements. So during peak lactation, milk yield will be high, the feed intake will not be sufficient and the animals lose body weight.
  • Nutritive requirements for milk production are in proportion to the amount of milk produced and are over and above those for other physiological phases of production such as maintenance, growth, fattening, fetal development, etc.

The major nutritive requirements for lactation are,

  • Protein: Must be of good quality at the glandular level. Animals will not produce milk low in protein. If ration is deficient in protein, tissue reserves of protein may be used for milk production
  • Energy: Energy over and above that for milk protein is required for the formation of milk fat and milk sugar. Must be in the form of net energy. May come from  carbohydrates, fat, or excess protein of the ration.
  • Minerals and vitamins

Wool production

  • Wool is practically pure protein and contains Sulphur containing amino acids.
  • The primary nutritive requirements for wool production are:
  • Protein: Must be sulfur-containing as fed or as synthesized in the rumen. 
  • Energy: This must be in the form of net energy and can come from any feed energy source. 
  • Potassium: This mineral is an essential component of the suint in wool. It is more than adequate in most ordinary rations.
  • Other minerals and vitamins:  


  • Nutritive requirements for development of foetus are energy, protein, calcium, phosphorus, and vitamin D in particular and other minerals and vitamins.
  • More than 2/3rd of the foetus growth occurs during the last trimester of pregnancy. Proper feeding during pregnancy is essential to avoid birth of dead foetus or weak foetus, to build up body reserves lost during early lactation and at the same time the animal should not become obese. 


  • Energy, protein, minerals and vitamins are required. 
Last modified: Friday, 30 March 2012, 9:31 AM