Misalliance is when a bitch is mated accidentally. If the owners do not want the pregnancy to continue then injections can be given to prevent this from occurring. The injections can be given up to 45 days after mating but the earlier they are given the less traumatic it is for the bitch. The course of two injections are given 24 hours apart and do sting slightly. As with any hormone treatment it can not be guaranteed 100% effective. Some bitches will come in to heat sooner than usual (usually after 3 months rather than 6 months). 

The best way to prevent this is to spay the bitch which involves removing the ovaries and uterus. This can be done anytime after the age of 6 months.