Why use lower urea for Breeders?


Why use lower urea for breeders?

Higher levels of urea used in the wrong situation can cost potential production as the animal is having to excrete the excess ammonia which comes at a high energy cost. Therefore, feeding high levels of urea can waste energy that would normally be used for production.

Most common non-protein nitrogen source is urea. It is a normal product of metabolism and is found in the animal’s body. It is produced in the liver from ammonia arising from amino acid metabolism in animals. Urea is secreted from the liver into the blood, filtered out in the kidney, and excreted in the urine. The feed version of urea is chemically made using carbon dioxide and nitrogen.

Urea is utilized by being converted to ammonia in the rumen by the action of microbial urease. Conversion of urea to ammonia is rapid, so there is a rapid increase in the rumen ammonia levels after consumption of urea-containing feed.

A major factor influencing the efficiency of urea utilization is the amount of readily available carbohydrate in the diet. Carbohydrates that are readily fermented are starches and sugars in cereal grains. Because urea is rapidly converted to ammonia it is important that the microbial population be able to utilize it rapidly. Otherwise rumen ammonia levels increase, ammonia is absorbed and may be excreted in the urine. This represents a loss of dietary nitrogen.

A vigorous microbial population will utilize ammonia rapidly and will also produce large quantities of organic acids. Absorption of ammonia is reduced to a low level when the rumen pH is 6 or lower. Ammonia released from urea breakdown increases the pH of the rumen.

Urea is not usually considered a satisfactory nitrogen supplement for low quality roughages. These highly fibrous feedstuffs do not support vigorous microbial growth, so the amount of ammonia utilized for microbial protein synthesis is low. Digestion of poor-quality roughages takes a fairly prolonged period, urea does not provide a continuous level of nitrogen in the rumen to sustain microbial growth. There is a peak of ammonia production after urea is consumed it is either utilized immediately in microbial metabolism or excreted. Hence the requirement for slow breakdown bypass proteins such as protein meals to help feed this population for an extended period for maximum utilization of low quality forages.

The degree of excess is greater in animals consuming low quality pastures because the rate at which microorganisms grow and synthesize protein is limited by the rate energy is obtained by plant-material digestion.

Fiber digestion reaches its peak 5 hours after ingestion of the feed, the urea delivery method must assure supplementary nitrogen during this time.

Fermentable Carbohydrates

  • Sugar, starch, pectin, fiber and a number of derivatives of these items provide a source of fermentable carbohydrate that rumen micro flora can degrade and with the addition of a nitrogen sources such as urea form a high-quality protein that that animal can use. Fermentable carbohydrates are not created equal the fiber portion or neutral detergent fiber (NDF) fraction on a feed analysis ferments slower than the other carbohydrates listed, which would appear as the non-fiber carbohydrate (NFC) this limits the use of urea in the diet because urea is very readily available. Therefore, a good quantity of NFC must be present to utilize the urea properly since the rumen micro flora can rapidly utilize this fraction and capture the nitrogen (ammonia) released from the urea. It is tempting to use urea to add crude protein to poor forage, but do so cautiously since without the readily available carbohydrate the urea may reduce energy availability of the forage. This is due to the excess urea requiring excretion through the manure to prevent toxicity, this process comes at a high energy cost to the body.


Products that contain a lower urea percentage have greater flexibility of providing higher levels of vitamins and minerals required in breeding herds. The main minerals that are viewed as important are below:



  • 80% of phosphorous in the body is found in the bones and teeth, with the remainder distributed among the soft tissues. Phosphorous is critical for optimal performance and is included in growth (appetite and feed conversion), reproduction and lactation. Also involved in energy production and has a role with calcium in bone formation.


  • Muscle contraction, nerve impulse and transmission. Formation of bones and teeth and is store in bones and mobilized when required.


  • Activates metabolic enzymes and is used in muscle contraction. Therefore, it is important during calving and body growth.


  • Present in protein, thiamine, biotin and enzymes. Used by rumen microbes for digestion. Required by rumen microbes when grazing dry feed to synthesis protein.


  • Required for normal cell and nerve function. Deficiencies can cause poor appetite and performance.


  • Formation of red blood cells and bones. Involved in immune response.


  • Involved in hoof production, skin health and enzyme systems. Immune function and sperm development


  • Works in conjunction with Vitamin E in cell metabolism. Involved in muscle function, fertility and immune function


  • Involved in numerous enzyme systems (bone and muscle function and reproduction)


  • Required for synthesis of vitamin B12 by rumen bacteria. B12 is required for energy production


  • Involved in oxygen transport in red blood cells and enzyme systems for energy production


  • Production of thyroxin hormone – controls metabolism, growth and fertility


  • Required for many enzyme systems





Cheeke, PR. (2005). Applied Animal Nutrition – Feeds and feeding Third edition. New Jersey,

USA Pearson Prentice Hall Upper Saddle River.


Dahlke, G. (2012). Protein Supplementation using urea. Retrieved 13/5/2020. From: Drovers

driving the beef market, https://aces.nmsu.edu/pubs/_circulars /CR583/welcome.html


Mathis, CP., Sawyer, JE & Waterman, R. (2003). Urea in Range Cattle Supplements.

Retrieved 13/5/2020. From: https://aces.nmsu.edu/pubs/_circulars/CR583/w elcome.html