The study was conducted on 40 calves of the Holstein breed where the calves were divided into 4 groups of 10 calves (5 male and 5 female). The aim of the research was to determine the influence of whey and sources of easily digestible proteins in starter mixtures on the production traits and development of the digestive system of early weaned calves. All calves were fed with the same milk replacer according to the same feeding plan, but each group was fed with a different pelleted starter mixture as follows: 1) control group (K) was fed with a control starter mixture; 2) experimental group 1 (P1) was fed with a starter mixture which contained dry whey; 3) experimental group 2 (P2) was fed with a starter mixture which contained yeast nucleotides, soy protein concentrate and two limiting amino acids - methionine and lysine; 4) experimental group 3 (P3) was fed with a starter mixture which containing dry whey, yeast nucleotides, soy protein concentrate and two limiting amino acids - methionine and lysine. Feed consumption was monitored on a daily basis and feed conversion was calculated from it. Body measurements, body weight, and blood sampling for biochemical and hematological analysis were performed at mean ages 6, 24, 50, and 91 days (procedure at day 91 was done only on female calves). On the same days, blood was taken for biochemical and haematological analyses. Male calves were sacrificed on the 56th day of age and after that slaughter and meat quality properties were determined. After sacrifice, rumen contents were taken for analysis of volatile fatty acid concentration and taxonomic composition of microbes, and rumen and intestinal tissue samples were taken for histological specimens and measurement of morphometric traits. The positive effect of the addition of whey and sources of easily digestible proteins in starter mixtures on the withers height of 91-day-old female calves, consumption of the mixture, biochemical parametars (glucose, urea, total protein, albumin, globulin, phosphorus and calcium) and haematological parametars (total leukocyte count, MCV, MCH and MCHC) of blood of 50-day-old calves. The addition of easily digestible protein sources to the starter mixture resulted in a lower concentration of isobutyric and isovaleric acid in the rumen content, and the addition of whey resulted in an increase in the proportion of Mitsuokella bacteria in the rumen content. The addition of whey and easily digestible protein sources to the starter mixture reduced the width of the rumen and ileum papillae, and the addition of easily digestible protein sources reduced the thickness of the ileum muscle. A positive effect of adding sources of easily digestible proteins in starter mixtures on the health of calves was found.