The problems caused by apparent overabundance of cow faeces (Turd world: how poo is mucking up the environment, 25 March) are at least partly in the control of the farmers, who feed a broadband insecticide (Dimilin) to their cows.

The purpose is to stop flies and beetles from feeding in the dung and thus breaking it down, a crucial step in the removal of the dung. Flies and beetles are thus no more a problem in intensive rearing units. Dimilin can remain active in the dung for a month or more, so when the dung is disposed of, it is still not possible for an insect (or many other species of arthropod) to survive or breed in it. Dimilin then becomes an added pollutant of run-off and water courses.

Its action is to disrupt the formation of a primary component (chitin) of the insect’s skin or shell. So the shell is never formed properly and breaks very easily, usually when the insect is expanding into its new shell after moulting. It can also affect the insect’s gut lining. I did some of the early work on Dimilin.

Julian Vincent

Bath

• David Cox says we need a systemic approach to the disposal of farm animal dung, but that the most obvious use in fertilising land faces real obstacles. These could, however, be avoided if dung were fermented instead of decomposed.

The right kind of fermentation (homolactic) kills bacteria so effectively that it even stops itself, producing a kind of pathogen-free preserve. When exposed to air, this becomes a harmless and attractive food for soil creatures, retains all of its original energy, carbon and nutrients, and smells sour rather than disgusting. It would make a perfect substitute for muck-spreading. The preserving process takes just a few weeks, as does the feeding frenzy in soil.

In America, you can buy household fermentation for pet poo. Scaling up to farming is a huge undertaking but is surely doable. Environment departments everywhere, take note. Humans can use this, too. Hygienic dry toilets instead of sewage, anyone?

Malcolm Fowles

Reading, Berkshire

• I notice you have not included the problem of greenhouse gas emissions from ruminants, or the huge agricultural acreages that meat production requires. Given the last UN report on global warming, it is surely the time to start taking serious action. A tax on meat and eggs would reduce the demand for meat, encourage veganism, and reduce the problems of poo, greenhouse gas emissions and inefficient use of agricultural land.

The tax could partly be used to subsidise independent butchers, and assist them to find other business opportunities. Farmers could also be helped to move towards greater crop production for human consumption.

As schoolchildren are telling us, time is running out for them, and it is time we started to take action. The dairy industry is probably too complicated for any change, but our lives will have to change in so many ways if we really want to stop global warming.

Philip Stringer

Lewisham, London

• It’s fair that your article should highlight the potential issues with conversion of animal poo into energy using anaerobic digestion (AD). Judging by the increasing number of UK companies seeking business angel funding in this area, I am pleased to say that market activity is strong. Many of the innovations pitched to us attempt to radically reduce a farm’s storage and operational footprint, in a move to so-called “micro AD”. The problems you outline are crucial, but business angels are helping many startup companies invest to resolve them.

Cam Ross

Director, Green Angel Syndicate

• Peter Duckers (Letters, 26 March) is only 129 years late in suggesting the House of Commons as a receptacle for cow poo. William Morris got there first in News from Nowhere, his fantasy of a future socialist society: “Use them [Houses of Parliament]! Well, yes, they are used for a sort of subsidiary market, and a storage place for manure, and they are handy for that, being on the water-side.”

Frank Jackson

Harlow, Essex

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