Can Natural and Synthetic Zeolites Be Dietary Modulators of Microorganism Population, Fermentation Parameters, and Methane Emission in the Rumen? A Preliminary Study on Cow

Zeolites are ‘magic stones’ with crystalline structures and unique properties, which enable them to selectively adsorb molecules, including gases. The aim of the study was to determine the effect of different types and doses of zeolites on microorganisms, nutrient digestion, and methane production in the rumen. The study was conducted on five two-year-old Jersey heifers (350 kg live weight) fistulated to the rumen in a 5 × 5 Latin square design divided into five feeding groups: control (basal diet), ZN2 (+120 g clinoptilolite/d), ZS2 (+120 g ZP-4A zeolite/d), ZN4 (+240 g clinoptilolite/d), and ZS4 (+240 g ZP-4A zeolite/d). During five periods of the experiment, the samples of the ruminal fluid and digesta were taken before and 3 h after feeding. The pH value, bacteria and methanogens populations, as well as short-chain fatty acids (SCFAs) and methane production in the rumen were not affected after zeolite addition (p > 0.05). ZN2 diet decreased the number of total protozoa by 41.2% (p = 0.023) and Entodinium spp. by 51.1% (p = 0.021), while ZS2, ZN4, and ZS4 diets reduced Diplodinium population by 70.5% (p < 0.001) 3 h after feeding in comparison to the control diet. An increased population of Ophryoscolex spp. was noted in ZN2 and ZS4 cow 3 h after feeding (p < 0.001; 0.15 × 10⁴/mL and 0.08 × 10⁴/mL vs. 0.02 × 10⁴/mL) when compared to control animals. Furthermore, ZS4 diet increased ammonia (p = 0.007; 3.97 mM/L vs. 2.27 mM/L), tryptamine (p = 0.014; 0.009 µmol/g vs. 0.007 µmol/g) and 1.7-diaminoheptane (p < 0.001; 0.016 µmol/g vs. 0.006 µmol/g) concentrations in the rumen, while phenylethylamine level was 90.9% higher in ZN4 cows (p = 0.007), in comparison to control, depending on time. To summarise, zeolites may act in a type- and dose-dependent manner on the protozoa population and indicators of protein degradation.