The American Society for the Prevention of Cruelty to Animals recently issued a Position Statement on Mandatory Spay/Neuter Laws, in which they state:
the ASPCA is not aware of any credible evidence demonstrating a statistically significant enhancement in the reduction of shelter intake or euthanasia as a result of the implementation of a mandatory spay/neuter law.
and
in at least one community that enacted an MSN law, fewer pets were subsequently licensed, likely due to owners’ reluctance to pay either the high fee for keeping an unaltered animal or the fee to have the pet altered