CO2 question

What's the smallest weight of rat that co2 can be used affectively on?

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I could be wrong, but I don't think that size is an issue with CO2.

Actually, pinkies and other very young rodents seem to be more resistant to CO2, I don't know why, they just don't seem to succumb quickly. But anything with eyes open seem to go down pretty easily. I don't know if it's because they're more active and use up oxygen quicker or what? It's just what I've observed.

I need to freeze 10 30 gram rats about 2 weeks old.

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If their eyes aren't open and they don't have much fur yet, put them in a ziplock and stick them in the freezer. 30 grams is pretty good size for only 2 weeks old.

They're 12 days old and most are about 22 grams. I need them between 25&34g.

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About another week and some of them may have their eyes open. You don't want to freeze one without gassing it first if it has a decent amount of fur, death would be too slow. But then again gassing the really young ones isn't really effective. Three weeks can be kind of a grey area. My personal preference is to gas the ones that have their eyes open and just freeze anything younger then that.

OK thanks. I will see if they're eyes are open at 30 grams.

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Do NOT use the freezer if they have any fur! Once they get fur, freezing is extremely inhumane and takes a long time. I've used CO2 on babies as young as 9 days, and they went down as quickly as the adults do.