Cod liver oil for horses – safe or not?
Although horses are herbivores, there is a number of animal products which have been fed to them for a long time and Cod Liver Oil is one of them. Cod liver oil is very high in Vitamin A (~100,000IU per 100g) and Vitamin D (10,000IU per 100g) and Omega 3 fatty acids (20g per 100g). At the same time, it is low in Omega 6 fatty acids (~1g per 100g) so has a very high Omega 3:6 ratio (~20:1). Omega 3 fatty acids have anti-inflammatory properties whilst Omega 6 are considered to be pro-inflammatory, although there is still a requirement for some in the diet.
These oils and vitamins can also be found in plant sources: for example, linseed is high in Omega 3, but in some circumstances, marine sources of Omega 3 are more beneficial. This is because Omega 3 is a “bucket” classification covering many types of Omega 3 fatty acids. In terms of anti-inflammatory properties ,when it comes to arthritis, skin disease and respiratory disease in particular, the most important ones are (EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), These are high in fish and shellfish (and hence cod liver oil) but low in plant sources of Omega 3.
There are several potential problems in feeding cod liver oil to horses. The first is palatability. Horses often don’t like fish products. However, it is possible to now obtain products/supplements which use deodorised fish oil or marine algae (which are also high in Omega 3 and EPA/DHA). The second issue is that oils can go rancid very quickly, further worsening their palatability and leading to loss of nutritional value.
The other potential issue is excess Vitamin A and D. Mature healthy horses not in work have a requirement of around 3000IU of Vitamin D per day. 30ml of cod liver oil would supply this and this does not allow for other intake of Vitamin D from the diet. For example, fresh pasture can supply anywhere from 30 to 2000IU per kg dry matter. Excess Vitamin D can be a serious issue for horses as it can be stored as cholecalciferol and lead to formation of calcium deposits in the arteries, heart, stomach, lungs and kidneys.
The Vitamin A daily requirement of a healthy mature horse not in work is around 30,000IU per day. This would also be supplied by 30ml cod liver oil per day, without taking into account any other sources in the diet. The natural foods horses eat do not contain Vitamin A, so this would only be present if added to feeds or supplements. However, horses’ diets do contain Beta-Carotene which can be converted to Vitamin A. Forages are the most important source of Beta-Carotene for horses. Excess Vitamin A is also toxic for horses and can result in bone fragility and abnormal bone development in young horses (developmental orthopaedic disease).
Bottom line:
Cod liver oil should be fed to horses with extreme caution. I would recommend a maximum of 10ml per day. Other sources which are high in Omega 3 EPA and DHA, such as deoderised algae, may be preferable for conditions such as arthritis, skin and respiratory disease as these do not provide potentially toxic levels of Vitamins A & D.
