The reality is that all animal cruelty and animal bestiality are difficult to prove because you don't have the core witness. That's always the issue. Prosecuting child sexual offences is also incredibly difficult when the children are very young. You just take that and extrapolate it to animals; it's the same thing. You don't have any witness, so essentially you're relying on other witness testimony.
To be honest, the only time we really get bestiality offenders is when they record it—it's video taped—because it's so impossible to get any evidence if it's done in private unless they either do it with other people around or they do it on video. The reason I suggested that it's a good idea to extend it to all forms of sexual conduct, which I think does make it slightly easier to prosecute, is that you're more likely to have a witness to sexual touching than you are to sexual penetration. That's why I believe that anything that can expand the definition is good.