The efficiency in rats will differ from that in mice, but in general nanoparticle reagents for siRNA in vivo delivery seem to work the best (see https://altogen.com/product/nanoparticle-in-vivo-transfection-reagent/). There are various protocols depending on the target tissue you are trying to silence a gene in, but broadly speaking there has been plenty of research published on in vivo siRNA delivery, which should help you find the optimal protocol for your research needs.

You can refer the below paper for your experiment, however you need to standardize the protocol. It worked for me.

S. Höbel, A. Aigner

Polyethylenimine (PEI)/siRNA-mediated gene knockdown in vitro and in vivo

Methods Mol. Biol., 623 (2010), pp. 283–297

Invivofectamine 2.0 or 3.0 reagent (Invitrogen) works well

You can use either or the following:

Liposome

Dendrimer

Polymeric nanoparticles

Invivofectamine

etc

It is going to depend on what cells/tissues or organs you want to target

I can suggest Magnetofection depending on your application, here are the information

http://www.ozbiosciences.com/8-in-vivo-delivery-transfection

Good Luck

The efficiency in rats will differ from that in mice, but in general nanoparticle reagents for siRNA in vivo delivery seem to work the best (see https://altogen.com/product/nanoparticle-in-vivo-transfection-reagent/). There are various protocols depending on the target tissue you are trying to silence a gene in, but broadly speaking there has been plenty of research published on in vivo siRNA delivery, which should help you find the optimal protocol for your research needs.