Wetenschap - 20 augustus 2010

One cow pie is better than another

Cow pies from organic dairy farms contain one and a half times as many insects as those in cow pies from conventional farms. This affects birds in these pastures.

Cow pies are a major source of food. Flies and beetles use the cow dung as ideal breeding places for their offspring. Pasture birds, such as the godwit and the peewit, would view them as the fairy tale wishing table which spreads itself with food. There seems to be differences, though, among the farm types the birds forage in.
What's on the menu?
Phd student Flavia Geiger (Nature Conservation and Plant Ecology) compared the cow pies of three types of farms: conventional dairy farm, organic dairy farm and natural terrains where cattle graze extensively. She writes about her findings in the latest issue of Entomologisch Berichten, in which she lists the ingredients in a normal cow pie. A cow pie from a common (conventional) farm has an average of 102 insects (and larvae). Cow pies from organic farms and in natural terrains with grasses are, by contrast, much richer in insects. Cow pies from these areas have an average of 156 and 168 insects respectively. That is therefore more than those in normal farms by half.
Geiger reports that the cow feed is the main cause of the differences among the farms. 'Cows in normal farms often get diarrhoea. Their dung is thinner and much less rich in fibres than those of cows in natural terrains. As such, there is less food for insects. But this is only a guess; we haven't researched into it yet.' Earlier research points to the negative effect of anti-worm medicines on insects. But this does not apply in this case. 'These medicines were not used on any of the inspected farms during the research.'
Pasture birds don't have it good in this country. The inferior quality of cow pies as food could be one of the reasons, explains co-author Geert de Snoo. According to him, a young godwit eats up to 8000 insects daily. 'As such, every little bit helps.' The Snoo is busy with getting a big follow-up research project off the ground.
Besides the inferior quality of the cow pies, other aspects which play a part are mowing and grazing practices. Geiger's research has established that pastures of normal and organic farms are mowed three weeks after grazing, on the average. Many insects are then still in their larva stage. Instead of being a delivery ward, Geiger says that such a cow pie would then become an 'ecological trap'.