J Anim Physiol Anim Nutr. 2020;00:1–14. wileyonlinelibrary.com/journal/jpn | 1 © 2020 Blackwell Verlag GmbH Received: 19 May 2019 | Revised: 8 November 2019 | Accepted: 11 November 2019 DOI: 10.1111/jpn.13297 ORIGINAL ARTICLE A multicomponent herbal feed additive improves somatic cell counts in dairy cows - a two stage, multicentre, placebo-controlled long-term on-farm trial Michael Walkenhorst 1 | Florian Leiber 1 | Ariane Maeschli 1 | Alexandra N. Kapp 1 | Anet Spengler-Neff 1 | Maria Teresa Faleschini 2 | Eliane Garo 2 | Matthias Hamburger 2 | Olivier Potterat 2 | Philipp Mayer 3 | Sandra Graf-Schiller 3 | Anna Bieber 1 1 Department of Livestock Sciences, FiBL, Research Institute of Organic Agriculture, Frick, Switzerland 2 Pharmaceutical Biology, Department of Pharmaceutical Sciences, University of Basel, Basel, Switzerland 3 SaluVet GmbH, Bad Waldsee, Germany Correspondence Michael Walkenhorst, Department of Livestock Sciences, FiBL, Research Institute of Organic Agriculture, Ackerstrasse 113, Frick 5070, Switzerland. Email: michael.walkenhorst@fibl.org Abstract In contrast to natural and historical diets of wild and domesticated ruminants, the diversity of plant species is limited in diets of modern dairy cows. Are “production diseases” linked to this? We conducted a trial to test the effects of a multicompo- nent herbal feed additive (HFA) on health, performance and fertility traits. A dose- finding study (DF) with 62 cows on 11 commercial farms compared a low (50 g) and a high (100 g) dose of HFA (HFA-50, HFA-100) with a placebo (PL). In a subsequent field trial (FT) with 280 cows on 30 commercial farms, HFA-100 was compared to PL. Cows were randomly assigned to HFA and PL groups and received HFA or PL individually daily from 14 days pre- to 300 days post-calving. Data were analysed with mixed effects models. No differences between HFA and PL were found regard- ing performance, body condition score and overall culling rates. A tendency towards lower milk urea for HFA-100 compared to PL ( p = .06) was found in DF. HFA signifi- cantly reduced elevated milk acetone observations (≥10 mg/L) in the first 10 lacta- tion weeks (HFA-100: 4%; HFA-50: 4%; PL: 12%) in DF. HFA-50 significantly reduced lameness incidence (HFA-100: 11%; HFA-50: 2%; PL: 14%) in DF. Calving intervals were 15 days shorter in HFA compared to PL in both trials, which could be confirmed by tendency ( p = .07) in FT. In both trials, the proportion of test days with elevated somatic cell score (≥3.0) was significantly lower in HFA compared to PL (DF: HFA- 100: 40%, HFA-50: 45% and PL: 55%; FT: HFA-100: 38% and PL: 55%) which is also reflected by tendency ( p = .08) in lower culling rates due to udder diseases in FT. HFA showed no negative impact on any of the measured parameters. The effects of HFA indicate a potential of phytochemically rich and diverse feed additives for dairy cows' nutrition and physiology. KEYWORDS bioactive compounds, dairy cows, feed additives, fertility, ketosis, udder health