[R] compare results of glms

[Sacha Viquerat]

dear list!
i have run several glm analysises to estimate a mean rate of dung decay 
for independent trials. i would like to compare these results 
statistically but can't find any solution. the glm calls are:

dung.glm1<-glm(STATE~DAYS, data=o_cov, family="binomial(link="logit"))

dung.glm2<-glm(STATE~DAYS, data=o_cov_T12, family="binomial(link="logit"))

as all the trials have different sample sizes (around 20 each),

anova(dung.glm1, dung.glm2)

is not applicable. has anyone an idea?
thanks in advance!

ps: my advisor urges me to use the z-test (the common test statistic in 
my field of research), but i reject that due to the small sample size.