Crude Protein and Non-protein Nitrogen Content in Dairy Cow Milk

Abstract

Abstract. Milk composition is of prime economic importance for farmers. Milk total proteins are composed of casein, whey proteins and non-protein nitrogen. The objective of this work was to establish milk crude protein, non-protein nitrogen (NPN) and urea content in dairy cow milk produced in different farms in Latvia. Cow milk samples (n=30) were collected in September 2012 from four different farms breeding diverse cow breeds. Average crude protein, casein and urea content in milk varied significantly among farms. NPN content in cow milk varies among farms -from 0.194% to 0.232%. Average crude protein and casein content was significantly higher (p<0.05) for Latvia Brown breed cows, while NPN content did not differ significantly among breeds. Regression between NPN and urea content in milk was R² = 0.458. Correlation between NPN and urea content was significant (r = 0.677). This study allowed establishing that crude protein and NPN content in milk varied significantly (p<0.05) in farms with differing dairy cow housing and feeding technologies. Key words: crude protein, casein, NPN, urea. IntroductionMilk of dairy cows is biological solution containing approximately 12.8% of dry matter. Milk dry matter consists of proteins, carbohydrates, fats, minerals and vitamins. Depending on animal breed, genotype, phase in lactation, nutritional value of feed, milking technology, animal health status, environmental conditions, animal age, interval between milking, as well as other factors milk composition may change (Coballero et al., 2003;Roginski et al., 2003).Recently increasingly higher interest has been devoted to researches on milk proteins, since they are the main component used to produce curd and cheese. Analysis of milk samples with standard Kjeldahl method helps in finding out volume of total nitrogen (N) in milk, and multiplying the acquired result by 6.38 we may acquire crude protein content in milk (ISO, 2001). Proteins in cow milk comprise 95 -97% of the crude protein content, and non-protein nitrogen (NPN) accounts for 3 -5%. Proteins in milk are represented by casein and whey proteins. Average proportions of proteins in crude protein are the following: 75 -85% casein, 18 -20% whey proteins. Casein content in proteins accounts for 85 -90% (Hui, 1993). Non-protein nitrogen (NPN) gets into milk from animal blood after protein metabolism. One of the largest (~50%) and most stable NPN parts is formed by milk urea. Apart from milk urea, NPN consists also of free amino acids, creatine, uric acid, peptides, organic acids and phospholipids (DePeter and Ferguson, 1992;DePeters and Cant, 1992;Твердохлеб и Раманаускас, 2006). Nutrition experts point out that evaluation of food quality from nutritional point of view requires finding out quality of proteins, as human body, unlike one of ruminants, may use only proteins formed from amino acids. Thus, the content of crude protein in milk should be taken into account when balancing diet; otherwise, expected results may not be achieved (Moughan, 2012).Lately interest tow...

Compositional and functional properties of milk and dairy products derived from cows fed pasture or concentrate‐based diets

“…Creatine, free AAs, uric acid, phospholipids, peptides and organic acids constitute the remaining 50% of NPN. These nitrogenous compounds are transferred from the cow's blood to milk following protein metabolism (Ruska & Jonkus, 2014) and, despite representing a small proportion of the overall nitrogen content of milk, the concentration of milk NPN is an important indicator of milk protein quality.…”

Variación del nitrógeno ureico en leche según la temporada del año y días en leche

“…Algunas investigaciones mencionan que el contenido de NUL en granjas holandesas varía de acuerdo con el tipo de alojamiento en el cual se encuentran los animales, aquellos de granjas más pequeñas y menos organizadas presentan un valor mucho más alto (5,24), y menciona además, que en esas regiones en los meses de verano el contenido de urea es significativamente mayor (24). Debido a las condiciones climatológicas de este país, es importante destacar que el régimen alimenticio durante este período cambia, ofreciendo a los animales alimentos más digeribles y con mejores concentraciones de nutrientes, lo cual afecta el comportamiento del NUL en estos rebaños, debido a la condición tropical de Colombia no existe propiamente la época de verano, sino dos períodos secos, en los cuales, debido a la poca tecnificación de las granjas nacionales no se ofrecen alimentos altamente aprovechables como los ofrecidos en Europa.…”

“…De la granja uno se seleccionaron 50 animales, con un peso promedio de 460.6±55.7 kg y un promedio de producción de 17. 5 la segunda granja, con un peso promedio de 452.5±42.3 kg y un promedio de producción de 18.3 kg leche/día/vaca. Sólo vacas con condiciones óptimas de salud fueron incluidas en el estudio, eso significó, sin cojeras, ni enfermedades respiratorias, reproductivas y de la ubre.…”

“…Debido a su pequeño tamaño, las moléculas de urea son capaces de atravesar las membranas celulares (incluidas las de la glándula mamaria) y llegar hasta la leche, allí toma el nombre del nitrógeno ureico en leche (NUL), que constituye entre el 2.5 a 3% del total del nitrógeno lácteo. Por tanto, NUL es derivado principalmente del NUS y está fuertemente relacionado con éste (4,5,6).…”

Study of the Different Ways of Proteins Extraction From Sheep and Cow Whey for “Urda” Cheese Production

“…The one of most valuable components of milk whey is whey proteins, which contents reaches 1,5 % [2]. Whey proteins contain all irreplaceable amino acids and their ratio corresponds to the full-value protein that fully provides all life needs of human organism [3,4]. Albumin milk, albumin sour-milk cheese, albumin mousse, cheese mass "Kavkaz" and so on are produced from whey proteins [5].…”