<PAGE>

                                 FIRST AMENDMENT
                                       TO
                      SECURED SUBORDINATED PROMISSORY NOTE
                           DATED AS OF APRIL 29, 2004

      This First Amendment is made as of the 24th day of March, 2005, by and
among Virbac Corporation, a Delaware corporation, PM Resources, Inc., a Missouri
corporation, St. Jon Laboratories, Inc., a California corporation, Francodex
Laboratories, Inc., a Kansas corporation, Delmarva Laboratories, Inc., a
Virginia corporation and Virbac AH, Inc., Delaware corporation (collectively,
the "Borrowers"), and Virbac S.A., a company organized under the laws of the
Republic of France (the "Holder") (capitalized terms used but not defined herein
shall have the meanings ascribed to such terms in that certain Secured
Subordinated Promissory Note, dated April 29, 2004, in the original principal
amount of $4,000,000.00 by and between the Borrowers and the Holder (the
"Note")).

      WHEREAS, the parties hereto desire to amend the Note as set forth herein;
and

      NOW, THEREFORE, for and in consideration of the premises and the mutual
covenants and agreements set forth herein and other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged by
each of the parties hereto, the parties hereto hereby agree as follows:

            1. The Note is hereby amended in all respects necessary such that
      Maturity Date shall be automatically extended for up to five (5) periods
      of three months.

            2. Except as provided for in this First Amendment, the Note, as
      amended, shall remain in full force and effect and is hereby reaffirmed.

            3. This Amendment shall be interpreted, construed and enforced in
      accordance with the laws of the State of Delaware.

                   REMAINDER OF PAGE INTENTIONALLY LEFT BLANK.
                             SIGNATURE PAGE FOLLOWS.

<PAGE>

         IN WITNESS WHEREOF, the undersigned have executed this Amendment
effective as of the date first written above.

                                      BORROWERS:

                                      VIRBAC CORPORATION
                                      A DELAWARE CORPORATION

                                      By: /s/ Jean M. Nelson
                                         -------------------------------------
                                      Name: Jean M. Nelson
                                      Title: Executive Vice President & C.F.O.

                                      PM RESOURCES, INC.
                                      A MISSOURI CORPORATION

                                      By: /s/ Jean M. Nelson
                                         -------------------------------------
                                      Name: Jean M. Nelson
                                      Title: Executive Vice President & C.F.O.

                                      ST. JON LABORATORIES, INC.
                                      A CALIFORNIA CORPORATION

                                      By: /s/ Jean M. Nelson
                                         -------------------------------------
                                      Name: Jean M. Nelson
                                      Title: Executive Vice President & C.F.O.

                                      FRANCODEX LABORATORIES, INC.
                                      A KANSAS CORPORATION

                                      By: /s/ Jean M. Nelson
                                         -------------------------------------
                                      Name: Jean M. Nelson
                                      Title: Executive Vice President & C.F.O.

                                      DELMARVA LABORATORIES, INC.
                                      A VIRGINIA CORPORATION

                                      By: /s/ Jean M. Nelson
                                         -------------------------------------
                                      Name: Jean M. Nelson
                                      Title: Executive Vice President & C.F.O.

<PAGE>

                                      VIRBAC AH, INC.
                                      A DELAWARE CORPORATION

                                      By: /s/ Jean M. Nelson
                                         ______________________________________
                                      Name: Jean M. Nelson
                                      Title: Executive Vice President & C.F.O.

                                      HOLDER:

                                      VIRBAC S.A.
                                      A COMPANY ORGANIZED UNDER THE LAWS OF THE
                                      REPUBLIC OF FRANCE

                                      By: /s/ Eric Maree
                                        _______________________________________
                                      Name: Eric Maree
                                      Title: President of the Management Board