my apologies I dashed these off quick this morning and only scanned them for errors without actually trying it my self, this version will work
CREATE TABLE `tbl_breedingschedule` (
`id` bigint( 20 ) unsigned NOT NULL AUTO_INCREMENT COMMENT 'Primary Key',
`maleID` bigint( 20 ) unsigned DEFAULT NULL COMMENT 'Foreign Key tblMales',
`bitchID` bigint( 20 ) unsigned DEFAULT NULL COMMENT 'Foreign Key tblFemales',
`dateMated` date DEFAULT NULL COMMENT 'Date Mated use <?php echo date("Y-m-d",time()); ?> or a calendar popup',
`dateDue` date DEFAULT NULL COMMENT 'Date Due use <?php echo date("Y-m-d",time()); ?> or a calendar popup',
PRIMARY KEY ( `id` ) ,
KEY `maleID` ( `maleID` ) ,
KEY `bitchID` ( `bitchID` )
) ENGINE = MYISAM DEFAULT CHARSET = utf8
A foreign key or fk is used to link tables together so in the example maleID would contain the ID value of the male dog taken tblMales and therefore becomes a foreign key in this table.
Yes the tables I gave you will work with the three tables you already have you just need to be able to link them, the dotted underlines in phpmyadmin so that there is a comment for that field.
Being able to write and understand sql statements is a required skill in designing and managing database driven applications, can I suggest that you get a copy of Sams Teach Yourself SQL in 10 Minutes which will teach you the core concepts that you need very quickly.