摘要：Determining urea concentration in milk is a useful indicator for controlling supply of proteins to organisms, as well as the relationship of energy and protein in the food, thus it is finding more and more ways of practical use. The concentration of urea in milk, along with the feeding process, is influenced by a number of other factors such as: breed, stage and sequence of lactation, body mass, daily production and chemical structure of milk, number of somatic cells, season, milking.The goal of the research was to establish the influence of the breed (Island of Krk, East Frisian), lactation stage (beginning, middle and the end) and the herd (3) to the concentration of urea in milk during lactation.For each breed there has been established daily quantity of milk, protein share and the concentration of urea in milk.Statistical analysis of data was conducted by using General Linear Models procedure, SAS program system (1999).The breed of sheep considerably (P<0.001) influenced daily quantity of milk, protein share and the concentration of urea in the milk.East Frisian sheep produced on average almost double the daily quantities of milk (1070 mL) compared to the Krk sheep (588 mL).Protein share and the urea concentration in Krk sheep milk were higher (5.99 % and 35.97 mg/100 mL) then in the milk of East Frisian sheep (5.12 % and 33.31 mg/100 mL).For both breeds the significant influence of lactation stage to the daily milk quantity has been established (P<0.001), that is also for the urea concentration in the milk of Krk sheep (P<0.001), as well as protein share in the milk of East Frisian sheep (P<0.001).Herd influence significantly affected daily milk quantities (P<0.001) and concentration of urea in the milk (P<0.05).The defining of the urea concentration in sheep milk should be occasionally carried out in the Republic of Croatia to establish the standard physiological values typical for the particular sheep breed.
