What is the meaning of the units used in PC-Horse?
 
One kilogram (kg) is 1000 gram
One milligram (mg) is 1/1000 of a gram, or 0.001 g
One microgram (mcg or ug) is 1/1000 of a milligram, or 0.001 mg
 
Some producers of horse feeds use the unit ug/kg when declaring the concentrations of nutrients like vitamin B12 or selenium.  
A B12 content of 100 ug/kg should in PC-horse be entered as 0.1 mg/kg, since most vitamins and trace mineral concentrations are presented in mg/kg.
The vitamins A, D and E are still declared as international units (IU) per kg of feed.
1 mg of vitamin E equals 1 IU. For the vitamins A and D there is no such simple relationship.

Can I feed carrots to my horse if it has laminitis?
For horses prone to laminitis you should try to limit the use of feeds that are high in starch (oats, barley, corn and mixtures of these) and feeds that are high in sugar. Carrots contain about 600 grams of sugar per kg of dry material. However, the carrot consists of 88% water and 12% dry material, i.e. one kilo of fresh carrots provides approximately 72 grams of sugar. Our best advice is therefore: a few carrots a day will not hurt, but you should keep the amount down to one kg per day for a 500kg  horse if it has problems with laminitis.