EMPLOYEE:

                                                                   Exhibit 10.84
                                                                   -------------

                      AMENDMENT TO RETENTION PLAN AGREEMENT

     This Amendment (the "Amendment") is entered into as of January 4, 2002
between Synbiotics Corporation ("Synbiotics") and the undersigned employee of
Synbiotics or its subsidiary ("Employee").

     A.   Synbiotics and Employee are parties to a written retention plan
agreement, as amended (the "Retention Plan Agreement"), under which Synbiotics
promised, on the day following the sale of Synbiotics' animal heath business, to
(i) make a cash bonus payment to Employee and (ii) accelerate the vesting and
provide a fixed exercisability period of all stock options issued to Employee.

     B.   Synbiotics is working toward entering into a Stock Purchase Agreement
with Redwood West Coast, LLC ("Redwood"), under which Redwood would make an
investment in Synbiotics stock (the "Stock Purchase Agreement"). Synbiotics has
determined that a closing under the Stock Purchase Agreement would constitute
the sale of Synbiotics' animal health business and entitle the Employee to a
cash payment of $_________ under the Retention Plan Agreement.

     C.   Redwood requires Employee and Synbiotics to enter into this Amendment
before Redwood will enter into the Stock Purchase Agreement. Employee and
Synbiotics wish to induce and facilitate the Stock Purchase Agreement
transaction.

     NOW, THEREFORE:

     1.   Synbiotics and Employee hereby agree that if and only if Synbiotics
and Redwood enter into the Stock Purchase Agreement, the Retention Plan
Agreement is hereby amended (as of immediately before the closing under the
Stock Purchase Agreement) by deleting the paragraph captioned "Cash Bonus" in
its entirety and replacing such paragraph with the following:

     "A cash bonus payment of $________ will be made to you on the earlier of
(i) January 1, 2003 or (ii) any date on which Synbiotics terminates your
employment without cause."

     2.   All of the terms and provisions of the Retention Plan Agreement as
amended hereby remain in full force and effect. However, Employee confirms that
upon Redwood's January 2002 investment under the Stock Purchase Agreement, the
Retention Plan Agreement (as amended hereby) is terminated except for
Synbiotics' obligations arising from such January 2002 Redwood investment.

                                   EMPLOYEE:

                                   _____________________________________________
                                   Name:  ______________________________

                                   SYNBIOTICS CORPORATION

                                   By: _________________________________________
                                       Xxxx X. Rosinack, President & C.E.O.