Effect of Two Feed Additives—One Multicomponent Based on Nanosilica and the Second Containing Mycelium of Lentinula edodes Fortified with Selenium—On Production Parameters and Histological Analysis of Calves’ Duodenum and Abdominal Rumen

SIMPLE SUMMARY: In the current study, we investigated the effects of two different additives on calves’ production parameters (body weight, average daily gain, average daily feed intake, and feed conversion ratio), hematological and biochemical results; serum selenium level, and histology of duodenum and rumen. A total of 18 1-day-old male calves were randomly assigned to control and two experimental treatments for 70 days. The first additive contained nanosilica with pancreatic enzymes, a mixture of fat-coated organic acids (fumaric, malic, citric, and sorbic acids), and sodium butyrate, whereas the second was based on the mycelium of L. edodes enriched in selenium. At the end of the experiment, three animals from each group were sacrificed for histological analysis of the digestive tract (abdominal rumen and small intestine). The findings of this study indicate that supplementation had no influence on growth performance, nor hematological or biochemical parameters. The additives did not increase duodenal crypt depth, villi height or width, or rumen papillae height or width. In the study, we observed higher levels of serum selenium and lower average daily milk replacer intake at 35–42 d but higher levels from 42 to 70 d in the animals receiving the inclusion of modified L. edodes mycelium. ABSTRACT: With this study, we aimed to evaluate the effect of two multicomponent feed additives given to animals from 10 to 70 d with milk replacer on the production parameters of reared calves: serum selenium level and histology of duodenum and rumen. The first additive was based on nanosilica (3000 mg) containing pancreatic enzymes (protease (18 mg), lipase (45 mg)), a mixture of fat-coated organic acids (2000 mg) (fumaric, malic, citric, and sorbic acids), and sodium butyrate (10,000 mg) (nanosilica/E/OA/SB), whereas the second was based on the mycelium of L. edodes (7 g) enriched in selenium (0.058 mg/g d.w.) (L. edodes/Se). The study was conducted on 18 male crossbred Holstein dairy calves from birth to 70 days of age, which were randomly assigned to control and experimental groups (six animals in each). From each group, three animals were sacrificed at 70 days of age, and histological analysis of the digestive tract (abdominal rumen and small intestine) was performed. It was observed that the additives used did not have any effect on growth performance and hematological or biochemical parameters. However, higher levels of selenium were found in serum in the calves fed with modified L. edodes mycelium on days 35 and 70 (44.33 and 51.33 µg/L in the control group and 132 and 93 µg/L in the L. edodes/Se group, respectively; p < 0.001). Moreover, we noticed lower average daily milk replacer intake at 35–42 d, which increased significantly from 42 to 70 d in the animals receiving L. edodes/Se.