Possible interferences of bentonite on rumen metabolome highlighted by 1H-NMR spectroscopy in dairy Holstein cows

In dairy cows, diet supplementation with clay minerals, such as bentonite, is a recognised method against the negative impacts of feed aflatoxin contamination on animal health and production, and on dairy products safety. Clay minerals are capable of binding mycotoxins, reducing their intestinal absorption and distribution in animal tissues and milk. Studies conducted in vitro and in non-ruminant animals suggested that clays do not adsorb specifically mycotoxins and they may affect intestinal absorption in other ways [1]. In ruminants, bentonite has been associated with decreased energy and crude protein digestibility and mineral imbalances [2], and it is suspected of modifying ruminal microbiota [3]. Therefore, more studies are needed in cows to verify possible interferences of clays with rumen fermentations and metabolite uptake, which may affect animal metabolism and, possibly, milk characteristics. The aim of this trial was to study the effects of bentonite administration on ruminal metabolome in the absence of aflatoxins. Six multiparous lactating Holstein cows (body weight: 658.5 ± 67.7 kg; DIM: 193 ± 23; milk yield 26.5 ± 4.8 kg/d) were included in a crossover 3×3 Latin square design at the end of a 24-d acclimatization period (t0). The design consisted of three 19-d periods (t1, t2, t3) and three treatments: control without bentonite (B0), prophylactic dose of 50g/day (B50) and therapeutic dose of 100g/day (B100) of bentonite (GLOBALFEED®T1). The cows were individually fed and received the same unifeed-based, aflatoxins-free ration. Bentonite was mixed with a small aliquot of unifeed and offered to the cows before feeding. A metabolomic analysis by 1H-NMR spectroscopy was performed on rumen fluid samples collected by ruminocentesis at t0 and on d 15 of each experimental period (OPBA authorization n. 0197903, 16/05/2019). Principal Component Analysis (PCA) on the ruminal metabolic profiles led to differentiate treated cows (B50 and B100) from the untreated ones (B0). However, the presence of carry-over effects can be hypothesised, in particular in animals that did not receive bentonite (B0) in t3. The concentrations of acetate, propionate, butyrate and lactate, measured on the 1H-NMR spectra, were analysed by a non-linear mixed model. A significant increase in acetate with increasing bentonite dose (p<0.05) and a significant decrease in propionate due to period effect (p<0.05) were observed. The results suggest an influence of bentonite on the metabolic profile of rumen fluid in dairy cows. On the other hand, insufficient wash out intervals between experimental periods cannot be excluded. Further analyses are in progress to identify the metabolites responsible for the PCA clustering. In conclusion, bentonite is not a completely inert additive, which can interfere with rumen metabolism with possible consequences on systemic and mammary gland metabolisms of dairy cows. (Funded by MIPAAF, DM 27443 - 25/09/2018 project BENFELAT)