A randomized clinical trial to examine hazelnut skin extract's effects on diarrhea and bronchopneumonia incidence, growth rate, antioxidant status, and fecal microbiota in neonatal dairy heifers

This study aimed to assess the impact of a 15-d administration of a polyphenol-rich extract from hazelnut skin (HS) on the incidence of neonatal calf diarrhea (NCD) and bronchopneumonia (BP) in Holstein heifers. Additionally, the study investigated whether the extract influenced reactive oxygen-derived metabolites (d-ROM), serum antioxidant capacity, fecal microbiota, growth rates, and severity of BP and NCD-related clinical parameters. In this randomized clinical trial, 80 healthy female dairy calves were allocated into 2 groups: a control group (CTRL, n = 40) and an HS-supplemented group (HS, n = 40), which received a milk replacer enriched with HS extract (5 g/day) from d 3 to d 18 of life. Daily clinical examinations were conducted for all calves until they reached 21 d of age. Additionally, thoracic ultrasonography (TUS) was performed at 21, 40, and 60 d of age, and weights were recorded at enrollment (d 3), 21 d, and 60 d. These repeated outcomes were analyzed using generalized estimating equations. Blood samples were collected from each calf at the beginning of the study and after HS (or control) administration for the evaluation of serum antioxidant capacity using the OXY-Adsorbent test and for determining d-ROM. Additionally, rectal swabs were taken from all calves at 2 (T0), 10 (T1), 18 (T2), and 24 (T3) days of life for the analysis of fecal microbiota. The duration of diarrhea in the CTRL group was 22% higher than in HS (incidence rate ratio = 1.22; 95% CI: 1.03-1.45). Calves in the CTRL group had higher odds of elevated fecal scores (odds ratio = 1.23; 95% CI: 1.02-1.52). At T21, median OXY values were 397.29 µmol (25th percentile [25°P] = 360.51; 75th percentile [75°P] = 426.30) in CTRL and 440.40 µmol (25°P: 400.97; 75°P: 479.14) in HS, with a significant difference between groups The ADG, fecal microbiota, d-ROMBP, disease incidence, and all clinical parameters evaluated were not affected by HS administration. In conclusion, these findings suggest that the administration of HS resulted in a reduction in the duration of watery feces during NCD episodes and an improvement in serum antioxidant capacity in treated calves. However, HS supplementation did not demonstrate any effects on the overall clinical health issues associated with NCD, lung lesions identified via TUS, or weight gain. Future research on HS supplementation in calves should be conducted over a more extended administration period and include comprehensive cost-benefit analyses.