Na temelju pregleda sadašnjih sustava procjene bjelančevinaste vrijednosti krmiva za preživače predlaže se zamjena dosadašnjeg sustava probavljivih sirovih bjelančevina s metaboličkim bjelančevinama u Hrvatskoj. Način procjene prati metabolički put bjelančevina u preživača koji je u obliku modela opisan u AFCR (1992). Metaboličke bjelančevine (MB) su jedinica bjelančevinaste vrijednosti krmiva koja se sastoji od u tankom crijevu probavljivih nerazgrađenih bjelančevine krme (PNRP) i mikrobnih sirovih bjelančevina (MSB). Sinteza MSB procjenjuje se na dva načina: (1) na temelju efektivno razgradljive bjelančevine (ERB) i (2) količine fermentirajuće metaboličke energije (FME). Kada je količina sintetizirane MSB iz ERB - MSP iz FME tada je ERB = MSB i obrnuto, za krmiva koja su sastojak obroka. Ukoliko se preživači hrane samo jednim krmivom (paša) bez dodataka tada je niža vrijednost MSB. Kao konstanta uzima se brzina oticanja digesta (r = 0.05/h) zato jer se preživači u Hrvatskoj hrane voluminoznim ili polukoncentratnim obrokom, a visina hranidbe nije veća od 2 x uzdržne potrebe. Količina FME (MJ/kg ST) = Me - (0.035 x MEᴍs + 0.015 x NRP ME ferm), a sinteza MSB (g/kg ST) = 10 x FME (MJ/kg ST). Data je tablica potrebnih koeficijenata (%) za izračunavanje MB: topivosti bjelančevina, razgradljivosti netopive bjelančevine i bjelančevina netopiva u kiselom detergentu (neprobavljiva nerazgradljiva bjelančevina za uobičajena krmiva u Hrvatskoj.Based on a review of present system of evaluation of protein value feedstuffs for ruminants, the exchange of the existing digestible crude protein system with metabolizable protein is suggested in Croatia. The method of evaluation follows protein metabolism in ruminants described as a model in AFRC (1992). Metabolizable protein (MP) is the unit of protein value of feedingstuffs consisting of in the small intestine digestible undegraded protein (DUP) and microbial crude protein (MCP). Synthesis of MCP is evaluated in two ways: (1) based on the effective degradable protein (EDP) and (2) the amount of fermentable metabolizable energy (FME) of feedstuffs. When the amount of synthesized MCP from EDP is – MCP from FME, then EDP = MGP and the reverse; that is valid for feedingstuff as a component of a diet. lf the ruminants are fed only single feedingstuffs (pasture) without supplements, then the value is lower. Rumen digest outflow rate (r = 0.R05/h) is constant because ruminants in Croatia are fed only forage of forage (r = 0.045) to concentrate (r = 0,058 ratio) 60:40% in diet DM, and r is 0.6*0.045+0.4*0.058 = 0.05; so the corresponding feeding level is not higher than 2x maintenance. The amount of FME (MJ/kg DM) = ME - (0.035xMEfat + 0.015 x UDP + MEferm) and synthesis of MCP (g/kg DM) = 10xFME (MJ/kg DM).Table of requirement coefficients (%) for calculation of MP is suggested: solubility of protein effective degradability of insoluble protein and acid detergent insoluble protein (indigestible undegradable protein) for common feedingstuffs in Croatia
