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

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.