Utilisation of Non Protein Nitrogen [NPN] Compounds in Ruminants  

Pashu Sandesh, 19 May 2025

Dr. Deepika Bhatia, Dr. Monika Karnani, & Dr. Manju

Department of Animal Nutrition  

Post Graduate Institute of Veterinary Education and Research, Jaipur

Abstract

In ruminant livestock system, nonprotein nitrogen molecules are an important nutritional strategy since they provide an affordable alternative to real protein sources. ruminants may transform NPN, mainly urea, ammonia, and biuret, into microbial protein through a symbiotic connection with the rumen microbiota. This microbial protein is then broken down and absorbed in the lower gastro-Intestinal tract. When NPN is properly incorporated into rations, it can improve the efficiency of nitrogen consumption, lower feed costs, and support ecologically friendly production system. The techniques for measuring nitrogen are unable to distinguish between NPN and nitrogen. Excessive intake or improper administration can lead to NPN toxicity, due to rapid hydrolysis of urea to ammonia in the rumen.

Introduction

Non protein nitrogen refers to a group of nitrogen containing compounds that are not protein and cannot be used for protein synthesis. Common compounds are urea, uric acid, creatinine, ammonia, peptides, nucleotides, nucleosides and free amino acids.

NPN in Ruminants 

The main way that ruminants and nonruminants vary from one another is through their digestive processes. Non ruminants can digest only real protein and use only them in their body. While ruminants can utilize all nitrogen compounds. NPN compounds are not protein but can be converted into proteins by microbes in the ruminant stomach.

Most commonly used NPN is urea.  urea is the simple compound that contains 46.7 percent nitrogen. Stomach physiology allows them to use a variety of protein sources. In order to build up their cells, rumen microorganisms manufacture protein from nitrogen-containing molecules. Ruminants employ this feature of the microorganism to partially or completely meet their protein needs from NPN compounds.

Animals with simple stomach are unable to utilize high amounts of NPN molecules. Because they lack the enzymes and bacteria necessary to break down NPN to ammonia and convert it to protein. 

The various NPN sources 

In the rumen, all NPN compounds produce ammonia, which travels to the liver and is ultimately transformed into urea.

The most common NPN -Urea

Urea is the major commercial source of NPN for use in ruminant feed. Using urea as a protein supplement in ruminant rations is cost effective when plant protein sources like soybean meal are expensive. Urea is a white crystalline substance that dissolve in water.

When added as a suspension or solution in molasses, urea can be used in solid feeds as well as when combined with liquid feeds. Urea stops bacterial growth and fermentation in concentrations over 10 percent. It has a bitter taste and limits intake if used at high level. 

When urea containing feed sources enters the rumen, bacterial urease quickly dissolves it and hydrolyses into ammonia. the bacteria can synthesize the amino acids they need to thrive by using the ammonia.

Morris stated that supplements of wheat and urea improved the survival rate and increased the roughage intake.

Rylay (1961) discovered that adding a small amount of sorghum, urea reduced body weight loss, improved birth weight of calves, reduced neonatal mortality and led to higher milk yields and calf growth rate.

Urea should not be included in concentration mixtures for sheep and cattle in excess of 3 % typically, 1 to 1.5 % will be sufficient. in their daily diet, cows can Ingest up to 272 grams of urea without showing any negative side effects.

Methods of urea ammoniation 

4 kg urea dissolved in 40 litre water and spray uniformly over 100 kg straw Preserve the treated material under air tight condition using plastic sheets for 3 weeks in hot season and 4-5 weeks in cold season.

Benefits of urea ammoniation 

• Increase the protein content.
• Improves the digestibility and palatability of straw.
• Better rumen degradability.
• Preservation of high moisture material preventing mould attack.
• Ammoniation facilitated lignin breakdown, enhancing the accessibility of structural carbohydrates and resulting in increased energy release and improved dry matter digestibility.
• The application of ammoniation markedly increased the apparent digestibility of dry matter, crude protein, hemicellulose, and cellulose in mature hay.

 Factors affecting urea utilization 

• The source of easily available carbs,
• Urea feeding frequency,
• Sufficient amount of sulphur & phosphorus and trace minerals, protein solubility.
• Addition of sulphur to urea supplemented diets to make the N: S ratio as 10: 1 improves utilization of urea.
• Addition of methionine also improves the urea utilization.
• Low levels of urea are better.
• It is also important that the other ingredients of the diet are not too high in NPN compounds which otherwise total ammonia release could be excessive for maximum efficiency.
• When the amount of protein in the basal ration is increased, the ability to utilize urea nitrogen decreases. The urea is very poorly utilized when it is added to concentrate mixtures containing greater than 18% CP and complete diets containing greater than 13% CP.
• Age of the ruminant animal.
• The nature of the protein in the ration may affect the utilization of urea nitrogen. The presence of highly soluble and easily hydrolysable protein in the diet depresses urea utilization.

 Biuret 

It is the compound derived from the condensation of two urea molecules. it degrades slowly. for microbial activity in the rumen, it is source of ammonium salt that easily releases ammonia. urea is heated to create biuret, which has 41 % nitrogen in it. due to rumen^’s gradual release of ammonia, it is not poisonous and only weakly soluble in water a 2 week to 2 months adaptation period is necessary before feeding a biuret response obtained. When the biuret is not fed, this adaptation quickly disappears. It is nontoxic so large amount of it can be safely consumed by animal without any difficulties. When biuret is given to ruminants eating low quality fodder on a daily or alternate day, it has no negative effects on the animal forage intake, nutritional digestibility, or microbial efficiency.

Limitations 

Suitable only for ruminants, it takes time for the rumen microorganisms to adapt. Requires a diet rich in energy in order to function properly.

A source of NPN for ruminants: poultry litter 

In the form of rumen-degradable uric acid, dried poultry faeces Has a high concentration of NPN and real protein.  Rumen microorganisms can use uric acid to produce proteins.  Poultry litter has a high content of CP (15–38%) and fibre (11–52%).  The amount of bedding materials and their quality determine how effective poultry litter is as a source of NPN.

Degradation of NPN sources by microbes 

The hydrolysis of NPN sources yields ammonia inside the rumen.  While biuret is broken down by the enzyme biuretase to produce urea and ammonia, Ureo lytic rumen bacteria generate ureases that catalyse the breakdown of urea to ammonia and carbon dioxide.  The primary sources of urease activity are rumen fluid and adhesive bacteria on the rumen wall. In low-protein diets, the increased hydrolysis and use of urea from blood is thought to be facilitated by the high urease activity of bacteria that adhere to rumen walls. Nucleic acids, nitrates, choline, and ethanolamine are among the most frequently found substances in ruminant diets.  In the rumen, nitrate reductase converts nitrates to nitrites, which are then transformed into ammonia.  Assimilation and dissimilation are involved in nitrate reduction.

Factors that impact the use of NPN sources 

Nutritional considerations and suitable rumen conditions are necessary for the effective hydrolysis and utilization of NPN molecules.  For ureo lytic bacterial activity, the ideal rumen pH range is 6.8 to 7.6; at higher or lower values, urea utilization falls linearly. Fermentable carbohydrate supply and the equilibrium between their release and ammonia availability are key factors in ammonia use.  Additionally, the amount of CP in the diet affects how well NPN compounds are utilized; a diet containing more than 14% of all digestible nutrients will result in a lower utilization rate.  Feed consumption and passage rate have an impact on NPN compound use.

NPN toxicity 

Ammonia toxicity may come from the rumen's extremely quick hydrolysis of urea to ammonia, which can outweigh the liver's capacity to convert it to non-toxic urea and rumen microorganisms use of it.  Animals who are either not acclimated to urea-containing diets are provided with a diet that contains an excessive amount of urea are most frequently the victims of ammonia poisoning.  A blood ammonia level of more than 20 mg/l and a rumen pH higher than 8.  Animals typically die when their blood ammonia levels rise above 40 mg/l.  Ammonia has harmful effects on the kidneys, heart, and central nervous system.

Signs of toxicity  

Dull depressed behaviour, muscle tremors, frequent urination and defecation, excessive salivation, increased salivation, increased respiration, ataxia, and tetanic convulsion. The electrolyte balance is also altered and acid – base imbalance Result from elevated ammonia concentration.

 Treatment 

adding an acidic solution to the rumen to counteract its high alkalinity.  In severe situations, fluid treatment and a rumenotomy can be necessary.

Nitrate /Nitrite toxicity 

For ruminants, nitrate is not poisonous in and of itself, but nitrites are highly hazardous. When ruminants consume a diet rich in nitrate, nitrite reductase's activity is not equal to that of nitrate reductase.  Consequently, the rumen's nitrite content surpasses the bacteria' capacity to transform it into ammonia, and it is taken up by the rumen wall and enters the bloodstream.

The animal develops anaemic anoxia when nitrite and haemoglobin combine to produce methaemoglobin, which is unable to deliver oxygen to the tissues.

Clinical signs of nitrate poisoning 

Hypoxia, dyspnoea, cyanotic mucous membrane, exercise intolerance, tachycardia, excessive salivation, vomiting, decrease weight gain, low body temperature, decreased milk yield and sudden death. abortion can also occur. It is possible for nitrate toxicity to be passed on to a new born calf if it is alive. It may also have seizures and convulsions.

Treatment 

I/V administration of methylene blue. While nitrate toxicity is decreased by using preventive measures.

Conclusion 

The total replacement of true protein with non-protein nitrogen sources in purified ruminant diets results in approximately a 35% decline in growth performance, feed conversion efficiency, and nitrogen utilization. Efforts to mitigate these adverse effects through supplementation with inpidual or combined amino acids, or alternative nitrogenous compounds, have largely proven ineffective in restoring performance to levels observed with intact protein inclusion.

Numerous studies have shown that poultry manure can save feed costs and maintain higher ruminant livestock output by replacing numerous pricey grain meal-based protein supplements and by serving as  a substitute for legumes during the dry season.  To produce animal protein from ruminants, it makes sense to use NPN for rumen-protein production and supplement with amino acids or protein that avoids the rumen.