초록
<P><B>Abstract</B></P> <P>Ruminal fermentation is accompanied by production of methane (CH<SUB>4</SUB>) and carbon dioxide (CO<SUB>2</SUB>) which are greenhouse gases (GHG) that cause environmental pollution. The effect of natural feed additives on the <I>in vitro</I> fermentation and production of CH<SUB>4</SUB> and CO<SUB>2</SUB> in dairy calf has had less attention. Therefore, this study aimed to evaluate the effect of garlic oil, xylanase enzyme, and yeast on <I>in vitro</I> biogas production from dairy calves fed a high concentrate diet. Rumen contents from 60-d old Holstein calves fed a concentrate diet were used as inoculum source. Garlic oil was included at 30,120, 250 and 500 μL/g dry matter (DM), while xylanase was included at 3 and 6 μL/g DM and yeast at 2 and 4 mg/g DM. The substrate used was the same as the diet fed to calves. Garlic oil linearly decreased (<I>P</I> < 0.05) <I>in vitro</I> DM digestibility and there were no differences among levels of either xylanase or yeast. Garlic oil decreased (<I>P</I> < 0.05) DM degradability while xylanase and yeast had no effect. The lag phase was linearly increased (<I>P</I> < 0.05) with increasing level of garlic oil. Garlic oil quadratically decreased CH<SUB>4</SUB> and CO<SUB>2</SUB> production. The control treatment had the highest CH<SUB>4</SUB> and CO<SUB>2</SUB> production followed by xylanase, yeast and garlic oil. Increasing level of xylanase and yeast increased (<I>P</I> < 0.05) CO<SUB>2</SUB> production. It can be concluded that garlic oil followed by yeast and then xylanase can be used to mitigate <I>in vitro</I> CH<SUB>4</SUB> and CO<SUB>2</SUB> production from dairy calves fed a high concentrate diet. However, further research is warranted to establish the efficacy of such feed additives in <I>in vivo</I> trials.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Garlic oil quadratically decreased CH<SUB>4</SUB> production. </LI> <LI> Xylanase, yeast and garlic oil decreased CO<SUB>2</SUB> production. </LI> <LI> Increasing level of xylanase and yeast increased CO<SUB>2</SUB> production. </LI> <LI> Natural additives can sustainably mitigate against environmental pollution by reducing greenhouse gas emission from calves. </LI> </UL> </P>