For the active immunisation of sheep and cattle against disease associates with infections caused by Clostridium chauvoei (BLackleg and post-parturient gangrene) Onset and duration of immunity have not been determined for this vaccine. 

Dosage & Administration
Dose - Primary Vaccination
Cattle: Two doses of 2ml administered 6 weeks apart, 2-3 weeks before expected period of risk.
Sheep: Two doese of 1ml administered 6 weeks apart, 2-3 weeks before expected period of risk.

Revaccination with a single dose is advised annually before the expected period of risk. 
Administration: By the subcutaneous injection preferably in the loose skin on the side of the neckl, observing aseptic precautions. 

Withdrawal Period
Zero days. 

Contraindictions, Warnings etc
Avoid stress in pregnant ewes and cows at vaccination. The vaccine has been shown to be safe and efficacious in sheep and cattle between 8 and 2 weeks prior to parturition. In the absence of specific data, no recommendation can be made for use of the vaccine during the first or second trimester of pregnancy.

Please see below link to the Veterinary Medicines Product Information Database
http://www.vmd.defra.gov.uk/productinformationdatabase/Default.aspx