Relative Difference in the Mean with a confidence interval

So I'm running an experiment that tests rodent's consumption of seeds. I had 7 groups of rodents that were randomly assigned either regular seed or seed treated with one of six rodent deterrents. I ran an ANOVA and Tukey to compare the groups. The results showed that rodents from the control group consumed 898 seeds on average whereas another group of rodents that received the strongest treated seeds consumed only 447 seeds on average. I would like to express these results as the phrase, "rodents from treatment group A consumed 50.2% less seeds than those from the control." {1-(447/898)=.502} Calculating the percent change is easy enough, but I would like to build a confidence interval around that relative percent change. Is there a simple way to calculate this? What metrics would I need to calculate it.