What age do your growouts hit 5 lbs? I was told to expect an average of 12 weeks. My current first batch of growouts are 8 weeks old in a few days, they all weigh in between 2 and 2.5lbs so far. I'm curious if this is on track or if they are behind.
Four to five pounds is generally considered butcher weight. Commercial New Zealands and Californians are expected to hit 5lbs around the 8-week mark. Rabbits bred on a smaller scale can vary widely. Satins tend to have a slower growth rate; they can take 12 weeks to get to 5lbs (with the advantage being that they eat quite a lot less, even comparing intake over 12 weeks to NZ intake over 8 weeks).
However, selective breeding can have a huge effect. I've been working on this for several years, and now my Satin bunnies are generally reaching 5lbs by 9 weeks, with some getting there at 7 weeks and others taking about 10 weeks. As I continue to work at it, that range should narrow.
I have found that mixed breeds (exception being NZ/Cal/Satin crosses) tend to have poorer growth rates and feed conversion rates than high-quality purebred meat breeds. Meat breeds have been rigorously selected for those traits; when you bring in a rabbit from stock that has not been, you tend to lose them quickly. Do note the "high-quality" modifier- there are a lot of breeders selling NZs and Cals that will not perform particularly well. But there is no reason you can't improve growth rates in your herd. (And note, bunnies with the best grow-out rates do not necessarily come from the biggest adults; you need to know how fast your breeding stock got