During the first months of extrauterine period calves are exposed to important anatomic-physiological changes in the digestive system by the introduction of solid foods which makes them functional ruminants. Considering that the development of rumen depends on the type of food and the nutrients structure objective of this study was to determine how an increased share of rumen undegradable starch and protein affects the production efficiency, biochemical and haematological parameters, acid-base status, morphometric measures of the rumen and small intestine mucosa, utilization of food protein and suckling calves health situation. Two experiments were carried out in the summer and winter period. Experiment 1 was conducted on 36, and experiment 2 was conducted on 30 Holstein breed calves, average age of 7 days, divided into three groups with equal sex ratio. Experiment was divided into two periods: starter mixture period which lasted for 39 days, and grover mixture period which lasted for 22 days. In starter period calves were fed with full pasteurized milk and milk replacer and additionally fed with starter mixture which ingredients differed depending on the proportion of rumen undegradable protein and starch: group I (36.6% RUP and 16.5% RUS), group II (49.1% RUP and 27.6 % RUS) and group III (53.5% RUP and 36.5% RUS). In grover period calves were fed with milk replacer and grover mixture which differed in groups depending on the different portion of rumen undegradable protein and starch: group I (33.5% RUP and 15.8% RUS), group II (48% RUP and 26.3% RUS) and group III (54.3% RUP and 34.6% RUS). Research has shown that higher concentration of rumen undegradable protein and starch positively affected the production indicators of calves; and the biggest impact was determined during the starter period of summer season. The increase of rumen undegradable protein and starch positively affected the complete blood count, rumen and ileum villi development, and health condition of calves.