Effects of the European Propolis Administration on the Growth Performance, Health Status, and Selected Blood Variables of Calves

<b>Background:</b> The effects of propolis supplementation on the performance of dairy calves are not well established. This study aimed to investigate the effects of oral propolis supplementation on the health status, growth performance variables, hematological parameters, and serum biochemical parameters of neonatal dairy calves. <b>Methods:</b> Twenty-four calves were enrolled in this study from 48 h after birth until 7 days of age. A complete clinical examination was performed daily by the same examiner. Blood sampling, body measurements, and lung ultrasonography were conducted on Days 0, 7, 14, and 28. The concentrations of albumin, total protein, total immunoglobulins, γ-globulins, triglycerides, total cholesterol, urea, creatinine, inorganic phosphate, and the activities of aspartate aminotransferase, alanine aminotransferase, and gamma-glutamyl transferase were measured. <b>Results:</b> Propolis supplementation had no significant effect on body weight, average daily gain, length, or height (<i>p</i> > 0.05). Pulmonary ultrasonography scores for subclinical pneumonia showed significant variation over time within each group (<i>p</i> < 0.05); however, no significant differences were observed between groups. Propolis supplementation significantly reduced the number of days with omphalitis in neonatal calves, likely due to its known anti-inflammatory and antimicrobial effects, although further studies are needed to clarify the underlying mechanisms (<i>p</i>=0.016). There were no significant differences in the number of days with fever or diarrhea between groups (<i>p</i>=0.44 and 0.15, respectively). No significant differences were found in blood variables between groups. Our results suggest that propolis supplementation did not positively affect growth performance or blood variables. <b>Conclusion:</b> Supplementation with propolis may be beneficial in reducing the incidence of omphalitis in neonatal dairy calves. Nevertheless, further studies are required to fully elucidate the effects of propolis.