Determination of N/Protein in Feed by Kjeldahl Method (CAT#: STEM-EA-0039-ZJF)

Introduction

Protein is a critical nutrient in cattle, pig, poultry, sheep, horse and pet foods. Although protein supplements are high cost they are sometimes necessary in order to meet the animal’s nutritional requirements. An adequate protein content in feed products is important for animal health and productivity, as well as for ranch profitability. The protein requirements of cattle vary with age, size, and expected performance. During lactation, larger cattle typically require more pounds of crude protein per day than smaller animals, but as a lower percentage of their total dry matter intake. In other words, lighter cattle require higher quality feeds and forages at lower quantities compared with heavier cattle. Cattle requirements for crude protein rise with increasing lactation and rate of gain. Protein is required for milk production and reproductive tract reconditioning after calving.
Kjeldahl is nowadays the most used method for determining nitrogen and protein contents in foods and feeds thanks to the high level of precision and reproducibility and to its simple application. The modern Kjeldahl method consists in a procedure of catalytically supported mineralization of organic material in a boiling mixture of sulfuric acid and sulfate salt at digestion temperatures higher than 400 °C. During the process the organically bonded nitrogen is converted into ammonium sulfate. Alkalizing the digested solution liberates ammonia which is quantitatively steam distilled and determined by titration.