It should be:
$UpdateQuery->bindColumn("horse_pic5", "s", "https://mysupersite.com/horse-sale-2020/".$WADAhorses_update->getColumnVal("horseid") ."/".($WA_DFP_UploadStatus["WA_UploadResult5"]["serverFileName"]) ."", "WA_BLANK");
Just make sure the WADAhorses recordset code is above this code.