Cobalt is naturally found in the environment, in plants and in the soil. It is present in animals and is a critically required trace element (metal). It is a structural component of Vitamin B12 (which also called Cobalamin), with 4.3 % of the weight of the molecule consisting of Cobalt. 

The horse has a dietary need of about 1 mg cobalt per day. This is easily obtained from typical horse feed as a typical 10 kg ingested by a horse every day contains between 1 to 4 mg cobalt. From this dietary Cobalt enough Vitamin B12 is produced by bacteria which are naturally present in the hind gut of the horse. This produced Vitamin B12 is available for absorption by the horse. 

The international, NHA adopted Cobalt thresholds for urine and for blood (plasma) are in place for the welfare of the racehorse. These two thresholds are matched in the clearance rate of Cobalt post administration.  Some racehorses previously tested overseas were officially confirmed to have dangerously high levels of Cobalt in their urine and blood.

 
Cobalt is found in a large range of registered oral and injectable veterinary supplements such as oral pastes, tonics, powders, injections and infusions. It has been shown that the administration of most Vitamin B12 and cobalt products increase blood and urine levels to exceed these thresholds for some period of time. The timing of the withdrawal of the administration of such products is therefore important in racing. 

The race day prosecution international threshold for urine is 100 ng/ml. This is while the untreated horse presents a urinary concentration of about 2 to 5 ng/ml Cobalt and while about 8 ng/ml is observed for a horse ingesting a cobalt fortified feed.            

 Vitamin B12 intravenous injections which are routinely provided to the horse are typically between 1 and 10 mg Vitamin B12. This corresponds to between about 0.05 mg and 0.5 mg Cobalt. Following such administrations urine Cobalt concentrations return to below the urine threshold after approximately 12 hours. The single treatment of horses with preparations such as Kyrophos Metabolic V, Kyrovital-15, Kyro B + Liver, Kyrovite B12, V-Tech Biosol-5, Catasol 10% and Rucenta Vitamin B Complex are likely to fall into this dose range. 

Studies have shown that if between 16 and 115 mg Vitamin B12 (0.7 to 5 mg Cobalt) is administered intravenously the threshold could be exceeded for about 18 hours.  When these corresponding doses are intramuscularly administered it could be exceeded for about 22 hours. This dose range applies to a high dose of Rucenta Vitamin B12 and injectables with about 5000 µg/ml Vitamin B12, such as Kyron Vitamin B12 Forte. 

The guidance for oral doses of Cobalt is somewhat different as relatively less of such ingested Cobalt is absorbed by the horse. An oral dose of 30 mg bio-available Cobalt exceeded the prosecution threshold for 28 hours while for a 44 mg dose it was 38 hours and for a 50 mg dose 48 hours. Note that the Cobalt introduced to the horse by recommended single doses of either the oral products Stride Hemo-Boost liquid or Pro-Dosa Boost paste are each less up to 1 mg, which corresponds to a detection time less than 12 hours. This while a normal dose of Red Cell is about 10 mg, which corresponds to a detection time of up to 24 hours. 

While the dietary need of the horse is only 1 mg per day, it has mechanisms to effectively and rapidly excrete Cobalt. Similar to other metals it is very toxic at high concentrations. Equine doses as high as 50 mg as injection or as oral administration are observed to only exceed the urine threshold for about 48 hours. 

The historic NHA recommendation for Cobalt administration remains much in place: 

• “It must always be checked that any injectable or oral multivitamin used must be checked for the presence of Vitamin B12 / Cobalamine / Cobalt.
• It is recommended that supplemental Cobalt from any source, including registered Cobalt containing supplements and Vitamin B12 / Cobalamine) is not be administered to the horse within at least two full days prior to a race day.
• Higher doses than those indicated by the particular product and also repeated administrations may require longer elimination periods.
• Multiple doses of Vitamin B12 / Cobalamine over a period of time and the use of high dose products such as those with “Forte, high dose” designations will necessitate a longer withdrawal period.
• There must be an awareness that the bio-availability and elimination of oral, intravenous, intramuscular and subcutaneous preparations are different and result in different extraction periods and different peak Cobalt levels.
• With many different Cobalt products used at the same time there will be a compounding effect as the Cobalt in each product would add to a higher total Cobalt dose.”