Fish oil is probably the most important supplement you can add to your dog’s diet, regardless of what type of diet you feed. EPA and DHA, the omega-3 fatty acids in fish oil, provide widespread benefits, but they are fragile and unlikely to survive storage in bags of kibble, or may be rancid even before being added to pet foods.
Proven benefits from EPA and DHA include:
Fish oil should be protected from light, heat, and air. Store liquid fish oil in dark bottles in the refrigerator. Purchase amounts that can be used within one or two months to avoid rancidity. If you notice an “off” odor, discard the oil.
Independent agencies have tested many human and pet supplements. None have found mercury, but a few products had unsafe levels of PCBs, provided less EPA or DHA than was shown on the label, or were spoiled. For those concerned about contaminants, look for molecularly distilled products (note the term “pharmaceutical grade” has no legal definition). More concentrated forms, with higher amounts of EPA and DHA per gram, result in lower levels of contaminants.
Liquid fish oil products made for humans often contain flavorings that dogs generally do not like.
Use products made for either humans or dogs. The amount of EPA and DHA in various fish oil preparations varies. Look for concentrated forms when giving high doses so you use smaller amounts of oil.
Healthy dogs can be given 100 to 150 mg EPA and DHA per 10 pounds of body weight daily; dogs who have health problems can be given up to 300 mg per 10 pounds of body weight. One ounce of canned fish with bones (sardines, jack mackerel, pink salmon) averages about 300 mg EPA and DHA combined.
The recommended dosage of liquid fish oil products is often too high, adding unnecessary fat and calories to your dog’s diet. High doses of fish oil can interfere with platelets and lead to increased bleeding, and too much can contribute to rather than reduce inflammation.
Cod liver oil is similar to fish oil, but most products also contain high levels of vitamins A and D (molecular distillation removes these vitamins). For those who feed a homemade diet that does not include much fish, give an amount that provides about 100 IUs of vitamin D per 25 pounds of body weight daily. Do not use high doses of cod liver oil. If additional omega-3 fatty acids are desired, add plain fish oil.