From: Oz <Oz@upthorpe.demon.co.uk>
Newsgroups: sci.agriculture
Subject: Re: Farming - How Much Acreage Necessary?
Date: Fri, 6 Feb 1998 07:00:05 +0000

In article <34DA442B.EC87B9BF@erols.com>, Rex Harrill
<brixman@erols.com> writes

>Of course, anyone who has noticed how assiduously cattle avoid the deep green
>grass near their droppings is already aware that they have very keen eyes
>indeed when it comes to not eating unhealthy vegetation full of nitrates.

I have never come across anyone who gets the wrong end of the stick so
beautifully.

Spread nitrates on half a field and your cows will all be out eating the
nitrate side preferentially to the untreated. The grass is leafier, more
full of proteins and sugars and takes less long to get a gutful. This
has happened here on numerous occasions.

Use manure instead of nice clean bug-free bag N and you see the reverse
for a few weeks. This has been known for centuries if you read archaic
farming books.

The reason has been known for decades. PARASITES. Cattle avoid eating
close to dungpats (but not urine'd areas) because millenia of natural
selection makes them avoid dungpats. This significantly reduced their
worm burden, because this has a dung to mouth step (strangely enough).

Now it's worth a small gasp of admiration for nature's ingenuity at how
some parasites try to negate this trick. Lungworm larvae (it's been a
while, so I may be out on the parasite) climb up onto a particular
species of dung-infecting fungi which spreads it's spores by firing (the
range is a foot or so high) it's spore-ball up into the air. Thus
carried by the spore-ball the larvae (at least a proportion) land
outside the avoidance zone and get eaten, thus completing the cycle. It
is worth noting that this is, as parasites go, a remarkably
straightforward survival trick, some are positively devious.

--
Oz