I did get this working on my own. Here is the code if anyone
wants to know.
<cfquery name="getdatedata" datasource="dairy">
SELECT MAX(std.DataDate) as DD1,
MIN(std.DataDate) as DD2,
DateDiff(d, MIN(std.DataDate), MAX(std.DataDate)) AS DDiff
FROM
(select top 2 datadate
FROM dairy.dbo.summarydata
WHERE FarmId='#form.farmid#'
AND
datadate between dateAdd("d", -28, #datevalue#)
and #datevalue#) AS std
</cfquery>
<cfoutput query="getdatedata">
#DD1#, #DD2#, #DDIFF#
</cfoutput><br />
<cfif getdatedata.DDiff LTE 0>
<cfset estgrowth="-">
<cfelse>
<cfquery name="getdataDD1" datasource="Dairy">
SELECT Paddock, DryMatter
FROM dairy.dbo.paddockdata
WHERE FarmID='#form.farmID#'
AND DataDate='#getdatedata.DD1#'
</cfquery>
<cfquery name="getdataDD2" datasource="Dairy">
SELECT Paddock, DryMatter
FROM dairy.dbo.paddockdata
WHERE FarmID='#form.farmID#'
AND DataDate='#getdatedata.DD2#'
</cfquery>
<cfset DD1numsamps="#getdataDD1.recordcount#">
<cfset DD2numsamps="#getdataDD2.recordcount#">
<cfset estgrowth=0>
<cfloop index="D1pad" From="1"
to="#getdataDD1.recordcount#">
<cfloop index="D2pad" from="1"
to="#getdataDD2.recordcount#">
<cfif #getdataDD1.drymatter[D1pad]# GT
#getdataDD2.drymatter[D2pad]# AND #getdataDD1.paddock[D1pad]# EQ
#getdataDD2.paddock[D2pad]#>
<cfset padavg[D1pad] =
(#getdataDD1.drymatter[D1pad]#-#getdataDD2.drymatter[D2pad]#)/#getdatedata.DDIFF#>
<cfset estgrowth=#estgrowth#+#padavg[D1pad]#>
</cfif>
</cfloop>
</cfloop>
</cfif>