Composition of crude protein content in milk | Kopproteīna sastāvs pienā
2014
Ruska, D., Latvia Univ. of Agriculture, Jelgava (Latvia). Inst. of Agrobiotechnology | Jonkus, D., Latvia Univ. of Agriculture, Jelgava (Latvia). Inst. of Agrobiotechnology
The most important milk components for dairy products are milk proteins. Now in Latvia the milk payment system is based on the content of total protein in milk and the amount of milk. Therefore the objective of the Latvian breeding programmes is high milk yields with high protein content. Normal bovine milk contains 30 to 35 g of protein kg-1. Milk crude proteins are composed of casein, whey proteins, and non-protein nitrogen (NPN) (DePeters and Cant, 1992). The two principal types of milk proteins are caseins and whey proteins (true proteins). Caseins constitute 76% to 86% of the total milk protein. Whey proteins represent 14% to 24% of milk proteins and are in solution in the serum phase of milk. Non-protein nitrogen represents approx. 5% – 6% of the crude protein (Hui, 1993). Urea is therefore a normal constituent of milk and comprises part of the non-protein nitrogen fraction. Urea accounts for roughly 50% of the non-protein nitrogen fraction in herd bulk milk of dairy cows, although this may vary from 35% to 65%. For milk from individual cows, this variation may be even larger (Bijgaart, 2003). NPN part in milk does not have nutritional and economic values. NPN part varies from 5.6% to 6.6% in Latvian farm milk. NPN values can be used to evaluate nitrogen utilization in farms. It is recommended to use casein or true proteins values to evaluate breeding efficiency and payment system.
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