Simple SummaryAccording to the latest estimate of the Food and Agriculture Organization of the United Nations, it is expected that by 2050 the world’s population will increase to 10 billion people, which will lead to a great increase in the demand for agricultural products. By this time, the world’s population will need 60–70% more animal products than it consumes today and, consequently, a high demand for feed will be required. Recently, the secondary use of the by-products of the processing industry, obtained as a result of the production of poultry meat, which can be included in the diets of farm animals, has become a popular topic in the feed industry. Russian veterinary legislation allows the use of poultry meat processing waste in the feeding of ruminants, which is consistent with EU Regulation No. 1069/2009 of 21 October 2009, which states: “Materials obtained from animals should not be fed to animals belonging to the species from which they were obtained”. Our research is developed to use a new feed (concentrate) from the remains of non-edible wastes (blood, heads, legs and internal non-edibles) together with plant proteins (white lupine grain) in feeding young cattle of the Russian Ayrshire cattle. This article describes the chemical composition of protein concentrate as an alternative feed in the calves’ diet and its effect on the bacterial microbiome, nutrient digestibility and biochemical parameters of calves and heifers.AbstractRecently, the secondary use of by-products of the processing industry resulting from the production of poultry meat, which can be included in animal diets, has become a popular topic in the feed industry. For studying the effects of partial replacement of rapeseed cake (RC) with the by-product source of animal protein concentrate Agro-Matic (PCAM) on growth dynamics, nutrient absorption and nitrogen balance, as well as blood biochemical parameters during the growing period, a total of 48 Russian Ayrshire dairy heifers were selected for this experiment and they were divided into three experimental groups (16 in each group, including the control group). The heifers of the control group were fed the basal diet which contained rapeseed cake (30%), while the second (RC + PCAM) and third groups (PCAM + RC) were fed the basal diet after replacing a part of the rapeseed cake with 2.25% and 4.5% of protein concentrate Agro-Matic respectively. The results showed that the weight of heifers treated with PCAM at 3 months of age exceeded the control by 2.3 kg (p> 0.05) in group 2 by 4.4 kg (p< 0.05). Similar results were obtained at the age of 6 months of raising. Feeding 4.50% protein concentrate Agro-Matic has a positive effect on the digestibility of nutrients; in particular, there was a significant increase in the digestibility of crude protein in the PCAM + RC group (77.23 vs. 73.42%) compared with the control group. Moreover, a similar trend was found in the digestibility of nitrogen in the diet. At the age of 3 months, heifers showed a significant decrease in the concentration of ketone bodies in the second group (1.82 vs. 2.20 mmol/L) relative to the control group. Urea was significantly lower in the RC + PCAM group (5.05 vs. 6.62 mmol/L) relative to the PCAM + RC group, while acid capacity (alkaline reserve) was higher by 2.41% (p< 0.05) relative to the control. In the 10th month of age, a positive effect on the blood of heifers was observed, as in the second and the third experimental groups, β-globulin and phosphorus increased (p< 0.05), while in the second group aspartate aminotransferase decreased (p< 0.05). Consequently, replacing the rapeseed cake with the protein concentrate Agro-Matic revealed an improvement in the dynamics of growth, nutrient digestibility and nitrogen balance, and it has an effect on improving some biochemical parameters of the blood.