According to Oregon, even though the dog might be owned by owner, if Humane Society draws blood from owner’s dog because someone complained the dog was “too thin”, they didn’t need a warrant.
but prior to this–the underlying Court said they did need a warrant:
“The court concluded that the “extract[ing] and testing” of Juno’s blood, even though Juno was lawfully in the state’s custody, was a constitutionally significant intrusion into defendant’s privacy, one that “exposed otherwise concealed information about the dog that served as evidence of a crime.” Id. at 271. Because the intrusion was not justified by any recognized exception to the warrant requirement, the court declared that the extraction and testing of Juno’s blood was an unlawful search under Article I, section 9. Id. at 271-72. The Court of Appeals therefore reversed defendant’s conviction and remanded the case to the circuit court.”
To stay out of trouble with animal control and private HO groups, the key is to make sure your animals, especially dogs [and horses] do NOT look “thin”, have matted fur, etc. Most seizures and arrests are generated by people that complain to animal control.