# What chemical odor resembles horse manure or "zoo smell?" **URL:** \ **Category:** Factual Questions\ **Created:** [July 30, 2019, 6:11am UTC](https://boards.straightdope.com/t/what-chemical-odor-resembles-horse-manure-or-zoo-smell/837863 "2019-07-30T06:11:16Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![Velocity](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/velocity/32/18006_2.png) [@Velocity](https://boards.straightdope.com/u/Velocity)\ **Post date:** [July 30, 2019, 6:11am UTC](https://boards.straightdope.com/t/what-chemical-odor-resembles-horse-manure-or-zoo-smell/837863/1 "2019-07-30T06:11:16Z")
So my neighborhood suddenly had/has this odor wafting around that rather strongly resembles the odor of horse manure or the “zoo smell.” Being a pretty urban place, I’m sure there are no horses, elephants or zebras around. What chemical might be responsible for this odor? ---
**Author:** ![Tim\_T-Bonham.net](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Tim\_T-Bonham.net](https://boards.straightdope.com/u/Tim_T-Bonham.net)\ **Post date:** [July 30, 2019, 9:18am UTC](https://boards.straightdope.com/t/what-chemical-odor-resembles-horse-manure-or-zoo-smell/837863/2 "2019-07-30T09:18:08Z")
One guess – somebody in your neighborhood has a landscape service that has fertilized their lawn with sheep or pig manure. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [July 30, 2019, 10:59am UTC](https://boards.straightdope.com/t/what-chemical-odor-resembles-horse-manure-or-zoo-smell/837863/3 "2019-07-30T10:59:43Z")
Personally, I bet you’re smelling 4-Ethylphenol, which is the compound which gives wine a “barnyard” nose. It could be from fertilizer, but also _Brettanomyces_ yeasts give it off, so spoilage in general could do it. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [July 30, 2019, 11:56am UTC](https://boards.straightdope.com/t/what-chemical-odor-resembles-horse-manure-or-zoo-smell/837863/4 "2019-07-30T11:56:15Z")
> [@MrDibble](#): > > Personally, I bet you’re smelling 4-Ethylphenol Probably combined with 4-Methylphenol. [Cite](https://academic.oup.com/chemse/article/36/6/539/478467). The methylated and the ethylated phenol in para-position was characterized by both a horse stable–like as well as a fecal odor attribute. ---
**Author:** ![mixdenny](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mixdenny/32/2962_2.png) [@mixdenny](https://boards.straightdope.com/u/mixdenny)\ **Post date:** [July 30, 2019, 2:47pm UTC](https://boards.straightdope.com/t/what-chemical-odor-resembles-horse-manure-or-zoo-smell/837863/5 "2019-07-30T14:47:50Z")
Composted mulch placed in landscaping smells just like that. Dennis ---
**Author:** ![racer72](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/racer72/32/3075_2.png) [@racer72](https://boards.straightdope.com/u/racer72)\ **Post date:** [July 30, 2019, 2:59pm UTC](https://boards.straightdope.com/t/what-chemical-odor-resembles-horse-manure-or-zoo-smell/837863/6 "2019-07-30T14:59:21Z")
> [@mixdenny](#): > > Composted mulch placed in landscaping smells just like that. > > Dennis As does beauty bark that has been in a big pile for a long time. My neighbor bought some discount beauty bark a few months ago, it stunk to high heaven till he removed all of it. ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [July 30, 2019, 7:51pm UTC](https://boards.straightdope.com/t/what-chemical-odor-resembles-horse-manure-or-zoo-smell/837863/7 "2019-07-30T19:51:47Z")
Ordinary composted material shouldn’t smell much if it is spread out loosely and allowed to dry. Too much “green” material can sometimes be an issue but bark-mulch materials are “brown”. This would leave having the wrong or insufficient microbes for composting. Pile it up loosely with some dirt to get things going right, then back to spreading it out. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [July 31, 2019, 9:18pm UTC](https://boards.straightdope.com/t/what-chemical-odor-resembles-horse-manure-or-zoo-smell/837863/8 "2019-07-31T21:18:51Z")
> [@MrDibble](#): > > Personally, I bet you’re smelling 4-Ethylphenol, which is the compound which gives wine a “barnyard” nose. It could be from fertilizer, but also _Brettanomyces_ yeasts give it off, so spoilage in general could do it. > [@MrDibble](#): > > Probably combined with 4-Methylphenol. [Cite](https://academic.oup.com/chemse/article/36/6/539/478467). > The methylated and the ethylated phenol in para-position was characterized by both a horse stable–like as well as a fecal odor attribute. Or [skatole](https://en.wikipedia.org/wiki/Skatole), 3-methylindole. ---
**Author:** ![mixdenny](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mixdenny/32/2962_2.png) [@mixdenny](https://boards.straightdope.com/u/mixdenny)\ **Post date:** [August 2, 2019, 4:36am UTC](https://boards.straightdope.com/t/what-chemical-odor-resembles-horse-manure-or-zoo-smell/837863/9 "2019-08-02T04:36:02Z")
> [@ftg](#): > > Ordinary composted material shouldn’t smell much if it is spread out loosely and allowed to dry. > > Too much “green” material can sometimes be an issue but bark-mulch materials are “brown”. > > This would leave having the wrong or insufficient microbes for composting. Pile it up loosely with some dirt to get things going right, then back to spreading it out. Maybe it shouldn’t smell but it stinks the whole street when I see it used. Dennis ---
**Author:** ![TruCelt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/trucelt/32/523_2.png) [@TruCelt](https://boards.straightdope.com/u/TruCelt)\ **Post date:** [August 2, 2019, 8:15pm UTC](https://boards.straightdope.com/t/what-chemical-odor-resembles-horse-manure-or-zoo-smell/837863/10 "2019-08-02T20:15:47Z")
> [@mixdenny](#): > > Maybe it shouldn’t smell but it stinks the whole street when I see it used. > > Dennis Agreed. Every Spring and Autumn I dread “Mulch Season.” ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [August 2, 2019, 8:28pm UTC](https://boards.straightdope.com/t/what-chemical-odor-resembles-horse-manure-or-zoo-smell/837863/11 "2019-08-02T20:28:29Z")
> [@mixdenny](#): > > Maybe it shouldn’t smell but it stinks the whole street when I see it used. > > Dennis If the odor source is intrinsic to the mulch source and not due to decomposition, then the guesses given above may be well off the mark. ---
**Author:** ![HMS\_Irruncible](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hms_irruncible/32/7394_2.png) [@HMS\_Irruncible](https://boards.straightdope.com/u/HMS_Irruncible)\ **Post date:** [August 4, 2019, 7:54pm UTC](https://boards.straightdope.com/t/what-chemical-odor-resembles-horse-manure-or-zoo-smell/837863/12 "2019-08-04T19:54:17Z")
When we had our yard done with landscaping manure, it smelled like dairy gutter muck suffused with urine and left to stand a couple of days. It smelled so bad that I almost wish it was fresh pig shit. Point being, I wonder if the urine is contributing much of that Iowa-pigsty-in-July smell. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [August 6, 2019, 12:23pm UTC](https://boards.straightdope.com/t/what-chemical-odor-resembles-horse-manure-or-zoo-smell/837863/13 "2019-08-06T12:23:46Z")
> [@Colibri](#): > > Or [skatole](https://en.wikipedia.org/wiki/Skatole), 3-methylindole. IME, skatole (and the releated indole) smell more like human shit and less like manure, IYKWIM. More like something from a carnivore/omnivore than a herbivore, basically. Although smell _is_ highly subjective. ---
**Author:** ![DCnDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dcndc/32/2842_2.png) [@DCnDC](https://boards.straightdope.com/u/DCnDC)\ **Post date:** [August 6, 2019, 12:26pm UTC](https://boards.straightdope.com/t/what-chemical-odor-resembles-horse-manure-or-zoo-smell/837863/14 "2019-08-06T12:26:14Z")
I don’t know that the chemistry is, but when we briefly had a pair of rabbits in the house, it seemed to be the combination of hay and urine that produced that classic “pet store smell.”