Cow farts, as I'm sure you know, are a related but different issue. Methane is not about particulates - it's a particularly harmful greenhouse gas. CH4 has approximately 23 times CO2 equivalence as a greenhouse gas, although it is shorter lived in the atmosphere. This is why waste managers have been trying so hard to move away from landfill, towards in-vessel composting for biodegradable waste for example. Cattle farming is especially wasteful and inefficient. Land that could/should give much greater calorific food yields when used for arable is given over to livestock, which then also emit large quantities of methane.
God, it feels like I'm back doing my old job at DEFRA. Snore....