The National District Attorneys Association published a guide to investigating & prosecuting animal abuse. Co-authored by Randall Lockwood, authority on foresnic investigation of animal abuse, this is an extremely useful resource for prosecutors. See the PDF version here.
Note: This source is outdated on its ALDF 50 state comparison of animal abuse. For the 2013 report, see here.
The American Society of the Prevention of Cruelty to Animals is the leading advocacy organization dedicated to combating animal cruelty and assisting cities and prosecutors in animal abuse cases. Their website is replete with information about animal cruelty, including a state-by-state search of animal cruelty laws. Additionally, if you are interested in reporting animal cruelty, assisting abused animals, or adopting rescue or shelter animals, this website is a great resource.
American Law Reports (ALRs) are annotations of law with helpful cases from multiple jurisdicitons. The following are ALRs relevant to the topic of animal cruelty:
1. 6 A.L.R. 5th 733, "What Consitutes the Offense of Cruelty to Animals". Practice guide resources can be difficult to find on animal cruelty, but this one is the best resource for compiling cases nationwide regarding animal abuse and cruelty. This is a great starting point for research on animal abuse and cruelty and how it compares from jurisdiction to jurisdiciton.
2. 68 A.L.R.6th 115, "Validity, Construction, and Application of Criminal Statutes and Ordinances to Prosecution for Dogfighting". Dog fighting is a specialized type of animal abuse that is commonly investigated and prosecuted. This American Law Report provides an in-depth comparison of cases about dog fighting and its prosecution, including prosecution for merely attending a dog fight in addition to organizing one.
Citations are from Westlaw.
1. 6 Animal L. 1: "Enacting and Enforcing Felony Animal Cruelty Laws to Prevent Violence Against Humans" by Joseph G. Sauder. This is a good explanation of the underlying public policy for criminalizing animal abuse, as well as the historical development of anti-cruelty laws.
2. 38 Idaho L. Rev. 177: Overcoming the Inadequacies of Animal Cruelty Statutes and the Property-Based View of Animals. This article examines the ideological gap between viewing animals as property, and reinforcing their worth by criminalizing abusing them. Note: this article confines the discussion to companion animals only.
3. 78 Miss. L.J. 1: Why is it a Crime to Stomp on a Goldfish? -- Harm, Victimhood and the Structure of Anti-Cruelty Offenses. This article is slightly outdated, but one of the most comprehensive in explaining why animal cruelty is criminalized. There is a thorough discussion of public policy reasons for punishing animal abuse.
4. 87 Iowa L. Rev. 1: Desecrating the Ark: Animal Abuse and the Law's Role in Prevention. This piece is animal rights- oriented in its tone and argument. It also fully explains the criminalization of animal cruelty and the penalties typically associated with committing an act of animal cruelty.
5. 88-NOV Fla. B.J. 30: Defending Those Who Cannot Speak: Civil and Criminal Prosecution of Animal Abuse. This piece is a call to action by an attorney that has been a public defender,a prosecutor, and a law professor. The author cites to important studies about animal abuse.
Citations are from Westlaw.