Elemental magnesium (Mg) can react with the acids of rumen fluid to produce Mg²⁺ and H₂. Mg is an essential nutrient to maintain normal life activities. However, it is also an important component of laxatives or antacids, and can cause diarrhea in animals. Therefore, elevated Mg²⁺ concentration may have negative effect on rumen fermentation.

Researchers from China Agricultural University and the Institute of Subtropical Agriculture (ISA) of the Chinese Academy of Sciences investigated the effects of elemental magnesium and magnesium oxide on hydrogen, methane and volatile fatty acids production in in vitro rumen batch cultures.

Scientists found that elemental Mg or MgO supplementation increased Mg²⁺ concentration and pH in comparison to the control without supplements. There was no statistical difference in ruminal Mg²⁺ concentration between MgO and elemental Mg supplementation.

Elemental Mg increased gH₂ and gCH₄ production as well as dissolved H₂ and CH₄ concentrations, in comparison to the control and MgO supplementation. Elemental Mg and MgO supplementation had lower initial fractional rate of degradation, fractional rate of gas production, gas production (GP) and volatile fatty acids (VFA) concentration than the control.

Furthermore, elemental Mg supplementation decreased GP and acetate molar percentage and increased propionate molar percentage, in comparison to the control and MgO supplementation.

This study indicated that high Mg²⁺ concentration (> 5.5 mM) inhibited ruminal fermentation. Extra H₂ produced by elemental Mg supplementation had a biological function to inhibit rumen fermentation, enhanced ruminal methanogenesis and shifted the fermentation pathway from acetate to propionate production.

The study, published in Animal Feed Science and Technology, was supported by the National Key Research and Development Program of China, National Natural Science Foundation of China, State Key Laboratory of Animal Nutrition, Hunan Province Science and Technology Plan, China Agriculture Research System, Youth Innovation Promotion Association CAS, and CAS President’s International Fellowship.