According to the documentation , it looks like you are looking for a parameter top.
<cfdump
var = "#variable#"
output = "browser|console|file"
format = "text|html"
abort = "true|false">
label = "text"
metainfo = "yes|no"
top = "number of rows|number of levels"
show = "columns|keys"
hide = "columns|keys"
keys = "number of keys to display for structures"
expand = "yes|no"
showUDFs = "yes|no">
top Optional 9999 Number of rows to display. For a structure, this is the number of levels displayed.
, CFM, keys
9999 .