You should always use condoms and lubricant for anal sex. While ejaculating doesn't matter from a disease standpoint, it is easier to spread STDs through anal sex than through vaginal sex, and as AnnieBrooke said, you get micro-tearing. If you don't use enough lube, you could get bigger tearing, which would hurt. It's also much easier cleanup if you use a condom. And don't switch from anal to vaginal without switching condoms, as that can cause an infection from putting anal bacteria in the vagina.
You are no more likely to get an infection from having your husband ejaculate in your bottom, than you are from having anal sex without ejaculation. The anus will accommodate a penis if there is plenty of lubrication, but if no lubrication you might get micro-tearing of the inside of the colon or the skin of the anus. If so, you could get an infection. But it is not from the ejaculate, it is simply from putting something big into a smallish space that needs time to stretch.
If you go from anal to vaginal sex in the same intercourse, your husband could put bacteria from your anus into your vagina. That might lead to a vaginal infection.
sorry was wondering if could get infection from ejaculate in your bottom. and if this is a safe thing to do ? or should he pull out to do this? anal sex has become need thing for us to do but I'm scared it might result in infections