Doses - ASPIRIN
Dogs: 
For analgesia: a) 10 - 25 mg/kg PO bid-tid (Morgan 1988)
b) 10 - 20 mg/kg PO q12h (Jenkins 1987), (Holland and Chastain 1995)
c) 11 mg/kg PO bid (Chastain 1987)
d) 11 - 26 mg/kg PO q12h (Kelly 1995)
As an antiinflammatory/antirheumatic:
a) 25 - 35 mg/kg PO q8h (Chastain 1987)
b) 25 mg/kg PO q8h (Holland and Chastain 1995)
c) Higher doses of up to 50 mg/kg q8-12h have been suggested for antirheumatic indications (Handagama 1986)
For antipyrexia:
a) 10 mg/kg PO bid (Morgan 1988); (Holland and Chastain 1995)
b) 11 mg/kg PO bid (Chastain 1987)
Post-Adulticide therapy for heartworm disease:
a) 5 - 10 mg/kg PO once a day (Morgan 1988)
b) 7 - 10 mg/kg PO once a day (Calvert 1987)
To decrease platelet aggregation/antithrombotic:
a) 0.5 mg/kg PO bid (Rackear et al. 1988); (Holland and Chastain 1995)
For Disseminated Intravascular Coagulation (DIC):
a) 150 - 300 mg/20kg animal PO once a day to once every other day for 10 days (Morgan 1988)
As an analgesic/antiinflammatory prior to elective intraocular surgery:
a) 6.5 mg/kg bid-tid (Wyman 1986)
Cats: 
For analgesia: a) 10 mg/kg PO every other day (Jenkins 1987); (Holland and Chastain 1995)
b) 10 mg/kg PO daily (Handagama 1986) ; (Davis 1985a)
c) 11 - 22 mg/kg PO q48h (every other day) (Kelly 1995)
For the treatment of arthritis/antirheumatic/antiinflammatory:
a) one 81 mg tablet ("baby" aspirin) PO in an average sized cat, on Monday, Wednesday, and Friday of each week. (Davis 1985a)
b) 25 mg/kg PO once daily (Chastain 1987); (Holland and Chastain 1995)
For antipyrexia:
a) 10 mg/kg PO q48h (every other day) (Holland and Chastain 1995)
For adjunctive treatment of hypertropic feline cardiomyopathy or intermediate (restrictive) feline cardiomyopathy (as an anti-thrombogenic agent):
a) 162 mg (two 81 mg "baby" aspirin or one-half 5 grain tablet) PO twice weekly (Harpster 1986)
b) 11 mg/kg PO every other day (q48h) (Chastain 1987)
c) As an anti-thrombotic: 25 mg/kg PO q56-84h (Holland and Chastain 1995)
As an analgesic/antiinflammatory prior to elective intraocular surgery:
a) 6.5 mg/kg bid-tid (Wyman 1986)
Cattle: 
For analgesia/antipyrexia: a) 50 - 100 mg/kg PO q12h (Jenkins 1987)
b) 100 mg/kg PO q12h (Koritz 1986)
c) Mature Cattle: two to four 240 grain boluses PO; Calves: one to two 240 grain boluses, allow animals to drink water after administration. (Label directions - Vedco Brand)
Horses: 
For analgesia: a) Mature Horses: two to four 240 grain boluses PO;
Foals: one to two 240 grain boluses, allow animals to drink water after administration. (Label directions - Vedco Brand)
b) 25 mg/kg PO q12h initially, then 10 mg/kg once daily (Jenkins 1987)
c) 15 - 100 mg/kg PO once daily (Robinson 1987)
Swine: 
For analgesia: a) 10 mg/kg q4h PO (Jenkins 1987), (Koritz 1986)
b) 10 mg/kg q6h PO (Davis 1979)
Avian:a) 5 grams in 250 ml of water as sole water source (Clubb 1986)
Note: Because of the significant hydrolysis that will occur, this solution should be freshly prepared every 12 hours if stored at room temperature or every 4 days if kept refrigerated at 5° C.
Monitoring Parameters -
Client Information - Contact veterinarian if symptoms of GI bleeding or distress occur (black, tarry feces; anorexia or vomiting, etc).
Because aspirin is a very old drug, formal approvals from the FDA for its use in animals have notbeen required (so-called "grandfather" drug). There is no listed meat or milk withdrawal timeslisted for food-producing animals, but because there are salicylate-sensitive people, in the interest ofpublic health this author suggests a minimum of 1 day withdrawal time for either milk or meat.
Dosage Forms/Preparations - Note: Many dosage forms and brand names are commercially available; the following is an abbreviated list of some products that have been used for veterinary indications:
Aspirin, Tablets, Children's; 65 mg (1 grain) and 81 mg (1.25 grains) in bottles of 36, 100, &1000 tabs (Note: some varieties are chewable; orange flavor)
Aspirin, Tablets; plain uncoated;325 mg (5 grain), or 500 mg (7.8 grain) in bottles of 12 - 1000 tablets
Aspirin, Tablets; buffered uncoated; 325 mg (5 grain), or 500 mg (7.8 grain) with aluminum&/or magnesium salts in bottles of 12 - 1000 tablets
Aspirin Tablets (veterinary) 60 grain (3.89 grams) in 100's
Aspirin Boluses (veterinary) 240 grain (15.55 gram) in boxes/bottles of 50
Rectal suppositories, and enteric coated or sustained-release oral dosage forms are also available commercially for human use. A combination veterinary product, Cortaba® (Upjohn), containing 300 mg of aspirin and 0.5 mg methylprednisolone per tablet is also available commercially.