The specific brand "Blue Ice" is trademark of Rubbermaid. (The
organization of the Rubbermaid site does not permit a direct link to
the Blue Ice products. However, if you type either the word "blue" or
the word "ice" into Rubbermaid's search engine, you'll find Blue Ice
products at the beginning of the results.)
However, "blue ice" more generally describes a kind of ice packs,
which are used in picnic coolers as well as to treat horses.
"Cold Therapy & Ice Bandages"
Big Five Veterinary Pharmaceutical Company
I have not found the chemical make-up of Rubbermaid's Blue Ice, but I
have found the composition of other "blue ice" products. Cold Comfort
Plus by 3M consists of "ammonium nitrate, water, propylene glycol,
methocel and FD & C blue 1".
Google cache of "Cold Comfort Plus"
A lesson sponsored by the Dow Chemical Company describes the process
of making a reusable ice pack that contains all of these ingredients
except ammonium nitrate.
"Dow/NSTA Summer Workshop Lesson Plan - Activity: Preparation of a
Reusable Ice Pack", by Kathleen Dombrink and Pam Fujinaka (1998)
MacKinnon Inc. describes a product designed specifically for horses as
containing "unique mix of polymers, food grade propylene glycol and a
low volume of water".
"New Leg Treatment Introduced" (revised 08 August 2002)
American Horse Publications
I hope that this information is helpful.
I used various combinations of these search terms on Google and Google
"cold pack" [or "cold packs"
"ice pack" [or "ice packs"]