Exhibit 2.4.1
                                                                   -------------

                                AMENDMENT NO. 1
                                      TO
                           ASSET PURCHASE AGREEMENT


     This Amendment No. 1 dated July 9, 1997, to the Asset Purchase Agreement
(the "Agreement") dated as of the 14th day of May, 1997 by and between
Synbiotics Corporation, a California corporation with its principal office at
11011 Via Frontera, San Diego, CA 92127 (the "Buyer"), and Rhone Merieux, Inc.,
a Georgia corporation with its principal office at 115 Transtech Drive, Athens,
Georgia 30601 (the "Seller").

     WHEREAS, the parties wish to amend the Agreement as set forth below to
reflect their agreement on the adjustment of the purchase price of the assets
being purchased thereunder, subject to the condition that the distribution of
certain products begin before the end of 1997.  Capitalized terms used herein
and not otherwise defined shall have the meanings assigned to them in the
Agreement:

     1.   Notwithstanding Section 1.1(a)(i) of the Agreement, the Buyer and the
Seller agree that the Seller shall not sell at the Closing, and the Buyer shall
not purchase, any inventories of finished goods or packing materials of the
"Witness" products, and Seller shall retain ownership of such finished goods and
materials and shall either (i) return such finished goods and materials to the
supplier thereof or (ii) sell such finished goods and materials to the Buyer
from time to time in accordance with Section 1.6 of the Agreement.

     2.   In Section 1.2 of the Agreement, the words "Four Million Two Hundred
Thousand U.S. Dollars ($4,200,000)" are replaced with "Two Million Eight Hundred
and Fifty Thousand U.S. Dollars ($2,850,000)".

     3.   The existing text of Section 1.2 of the Agreement is redesignated as
paragraph (a) of Section 1.2. and the words "provided that if... " through "as
soon as practicable," are deleted.  The following new paragraph (b) is added
thereafter:

          "(b) (1) If, prior to January 1, 1998, (i) the Buyer or any of its
          Affiliates makes a commercial sale in the United States of any
          Heartworm Product (as defined below), approved for sale by the USDA in
          any form, or (ii) if the U.S. patent rights on technology relating to
          any Heartworm Product are licensed, sublicensed or given by the Buyer
          or any of its Affiliates to any third party (other than for the sole
          purpose of enabling such third party to manufacture or resell
          Heartworm Products on behalf of the Buyer or one of its Affiliates),
          the Buyer shall immediately inform the Seller of such event and pay to
          the Seller a sum equal to the 

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          product of One Hundred Thousand U.S. Dollars ($100,000) times the
          number of full calendar months between the date of such event and
          December 31, 1997, by wire transfer of immediately available funds to
          an account designated by the Seller no later than thirty days after
          the date of occurrence of such event. If, prior to January 1, 1998,
          (i) the Buyer or any of its Affiliates makes a commercial sale in the
          United States of any FeIV Product (as defined below) in any form, or
          if the U.S. patent rights on technology related to any FeIV Product
          are licensed, sublicensed or given by the Buyer or any of its
          Affiliates to any third party (other than for the sole purpose of
          enabling such third party to manufacture or resell FeIV Products on
          behalf of the Buyer or one of its Affiliates), then Buyer shall
          immediately inform the Seller of such event and pay to the Seller
          Three Hundred and Fifty Thousand U.S. Dollars ($350,000) by wire
          transfer of immediately available funds to an account designated by
          the Seller no later than thirty days after the date of occurrence of
          such event. For purposes of this Agreement the terms "Heartworm
          Product" and "FeIV Product" shall mean the Witness Heartworm product
          and the Witness FeIV products, respectively, of the Seller as they
          existed in their form of an antigen caught in between two monoclonal
          antibodies on the date of the Closing and as such products may be
          modified from time to time by or for the Buyer, regardless of the
          trademarks under which these products are sold.

          (2)  If, before January 1, 1998, the Buyer obtains from a third party
          a patent or technology license in order to avoid patent or technology
          infringement claims in connection with the commercial introduction in
          the United States of an FeIV Product, the cost of such license
          (including all up front payments and the net present value discounted
          at an annual rate of 14% of all future royalties or other similar
          payments due from the Buyer or its Affiliates to the licensor for a
          period of the remaining duration of the patent or four (4) years,
          whichever is shorter), up to a maximum of One Hundred and Seventy-Five
          Thousand U.S. Dollars ($175,000), shall be deducted from the Three
          Hundred Fifty Thousand U.S. Dollars ($350,000) to be released in
          connection with the corresponding FeIV release, and no price
          supplement shall be due by RM under new Section 1.6 of the Stock
          Purchase Agreement, as amended.

     4.   Clause (d) of Section 1.6 is amended by adding to the end thereof,
before the semi-colon, the following "or return any items of Retained Inventory
to the manufacturer."

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     5.   Section 1.7 of the Agreement is deleted.

     6.   Section 6.9 of the Agreement is deleted.

     7.   The first clause of Section 8.5 of the Agreement up to the first
proviso, is amended to read as follows:

          "8.5 Limitations on Liability.  The liability of the Seller for
          indemnification hereunder shall be limited to the sum of (a)
          $13,533,690 plus (b) all amounts paid to the Seller pursuant to
          Section 1.2(b) of this Agreement, plus (c) the amount of the Earn-Out
          Payment, if any, actually paid to RM pursuant to the Stock Purchase
          Agreement (collectively the "Indemnification Amount");".

     8.   The Buyer hereby waives for itself and for any of its Affiliates any
rights it or they may have under Section 8 of the Agreement as a result of any
claim or action by any third party alleging an infringement of a United States
patent or U.S. intellectual property rights arising out of any sale after the
Closing by the Buyer or its Affiliates or licensees of Heartworm Products or
FeIV Products.  The Buyer hereby represents that it is aware of the risks of
U.S. patent infringement associated with these products and assumes such risks
to the extent set forth in this Section 6.

     9.   This Amendment No. 1 may be executed in one or more counterparts, each
of which shall be deemed to be an original, but all of which shall be one and
the same document.

IN WITNESS WHEREOF, this Amendment No. 1 to the Agreement has been duly
executed by the parties hereto and is effective as of the date first above
written.


                                       SYNBIOTICS CORPORATION

                                       By:  /s/ Kenneth M. Cohen
                                            --------------------
                                            Name: Kenneth M. Cohen,
                                             President and Chief Executive
                                             Officer


                                       RHONE MERIEUX, INC.

                                       By:  /s/ Kyle W. Lathrop
                                            -------------------
                                       Name: Kyle W. Lathrop
                                       Title: General Counsel/Proxy

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