Asparagus pee smell had a fun side effect documented since at least 1702 when Louis Lemery has written about this in the Treaty of all kinds of food. Vegetables (which was once classified as part of the lily family) is very healthy and low in calories and sodium count. Asparagus contains a wide variety of vitamins and minerals and has diuretic properties, as well as, about 20 000 years of history used as a medicine (and vegetable) in Egypt. In addition, it is nice on a plate.
As if this were not enough, the asparagus is also a laxative. And high levels of Folate are an excellent source of food for pregnant women (or those who try to) and may protect against Alzheimer's disease. Also, water, in that asparagus has been cooked can reduce the incidence of spots (face) if used regularly to wash! It is an amazing vegetable and why people might want to feed their pet remains is not surprising.
The secondary effect well known and had fun on this very healthy vegetable is its effect on urine odours. As little as 15 minutes after the change of the smell of urine of consumption is obvious to the people with the olfactory gene or chromosome to be able to detect the smell. Apparently, more than 20% of people have this gene. But all those who consumes the vegetable smell of urine altered.
There are a number of compounds in asparagus that our body metabolizes in the process of digestion. Most of these began as asparagusic acid (and derivatives) in asparagus. The body then produces organic compounds that are volatile or airborne (and therefore waft up and are eventually discovered by the nose). These compounds are what the smell of pee altered can be attributed to. I don't know the chemical composition or the structure of these compounds, but Wikipedia lists some of them such as methanethiol, dimethyl sulfide, dimethyl disulfide, bis (Methylthio) methan, dimethyl sulfoxide, dimethl sulfone.
I do not think that you must be a chemist to have heard that methane that cows produce to their sides and is responsible for the smell of rotten eggs - it's smelly, as is anything sulfur there. Adding what either in your diet that turns into methane or sulphur as compounds in your body will change scents that come out of your back as well.
I wanted to write about what happens to the scent of dog urine after a puppy has eaten with asparagus. Curiously I found no scientific study on this... perhaps that people are too busy to the study of our faltering economy to take the time to do scientific work on the smell of urine smell or dog urine from the popular.
Dogs can eat asparagus - it is not toxic. It seems that some vegetables give some bad flatulence mad dogs (just as some people who are in need of a couple caplets Beano to avoid the spread of their vegetables people methane induced their sides). And anecdotal evidence from the internet suggests that dogs will produce only of asparagus distinctive pee smell. That something like 20% of the population can feel this effect, even from the dogs pee. If you cannot feel urine asparagus after you've eaten the vegetable so it is probably safe to feed your dog without worrying about how to modify your backyard odors... But keep in mind that about 20% of your neighbors may notice a small perfume of "not quite right" if they have the asparagus pee smell olfactory gene!
Sonya manages the website http://www.PeeSmell.com. it has been a friend and provided a home for many animals over the years.