The active ingredient in
Dow Doxstar Pro looks to be fluroxypyr (is that the same as asulam, Sally?),
and there's a fair bit of information on it here.
The most relevant pieces of information I can see are:
Mammals - Acute oral LD50 (mg kg-1) > 2000
Mammals - Short term dietary NOEL (mg kg-1) > 80
Soil degradation (days) (aerobic) DT50 (typical) 13.1, Non-persistent
DT50 (lab at 20oC) 13.1, Non-persistent
DT50 (field) 51, Moderately persistent
Dissipation rate RL50 on and in plant matrix 5.5
What that means in practical terms is that it doesn't degrade all that quickly when applied to plants or soil (some of these substances degrade extremely quickly in daylight, which is a great thing - they do their job and then promptly disappear!). However, there is presumably a decent length of time between spraying the fields and haymaking, and again a good length of time between haymaking and Daisy munching it, so that will significantly reduce the concentration she is exposed to.
To (badly) interpret the toxicology data, If Daisy weighs 400kg, you'd have to force feed her 800g of the stuff as a still-active ingredient to give her a 50% chance of death. Also, looking at the "NOEL", which is the anticipated no-effect-level, you could feed her up to 32g of it on a short term basis and expect to see no effect on her health whatsoever
. Practically, I don't see how you could feed her anywhere near that amount, even if you tried (you could even do a BOFP* calculation based on the field application rate and hay yield per hectare to put your mind at rest, if you felt so inclined).So, if fields can be grazed a week after application, and that's been tested as safe for both animal and human health, it seems to me that the dose Daisy receives will be significantly smaller. The same goes for any lettuces grown in affected dung or horse muck.Of course, it's hard to relate that directly to concentrations in milk, and subsequently any health effects on people who drink it. However, I'd cheerfully drink a pint of milk alongside my lettuce sandwich, and would not worry in the slightest.
Does that help? It certainly passed ten minutes for me when I should have been doing something else less interesting!*Back of Fag Packet