<PAGE>

                               FIFTH AMENDMENT TO
                                CREDIT AGREEMENT

      THIS FIFTH AMENDMENT TO CREDIT AGREEMENT, made and entered into as of the
11th day of August, 2003, by and between VIRBAC CORPORATION, a Delaware
corporation ("Virbac"), PM RESOURCES, INC., a Missouri corporation ("PM
Resources"), ST. JON LABORATORIES, INC., a California corporation ("St. JON"),
FRANCODEX LABORATORIES, INC., a Kansas corporation ("Francodex"), and VIRBAC AH,
INC., a Delaware corporation ("Virbac AH," and collectively with Virbac, PM
Resources, St. JON and Francodex referred to herein as the "Borrowers"), and
FIRST BANK, a Missouri state banking corporation ("Bank").

                                   WITNESSETH:

      WHEREAS, Borrowers heretofore jointly and severally executed and delivered
to Bank a Revolving Credit Note dated September 7, 1999, in the principal amount
of up to Ten Million Dollars ($10,000,000.00), payable to the order of Bank as
therein set forth, which Revolving Credit Note has been most recently amended
and restated by that certain Revolving Credit Note dated August 7, 2002 in the
original principal amount of up to Twelve Million Dollars ($12,000,000.00) (as
amended and restated, the "Note"); and

      WHEREAS, the Note is described in a certain Credit Agreement dated as of
September 7, 1999 made by and among Borrowers and Bank, as previously amended by
an Amendment to Credit Agreement dated as of December 30, 1999 made by and among
Borrowers and Bank, by a Second Amendment to Credit Agreement dated as of May 1,
2000 made by and among Borrowers and Bank, by a Third Amendment to Credit
Agreement dated as of April 4, 2001 made by and among Borrowers and Bank, and by
a Fourth Amendment to Credit Agreement dated as of August 7, 2002 made by and
among Borrowers and Bank (as amended, the "Loan Agreement," all capitalized
terms used and not otherwise defined herein shall have the respective meanings
ascribed to them in the Loan Agreement); and

      WHEREAS, Borrowers and Bank desire to increase the amount of the loans and
to make certain other amendments thereto on the terms and conditions set forth
herein;

      NOW, THEREFORE, in consideration of the premises and the mutual provisions
and agreements hereinafter set forth, the parties hereto do hereby mutually
promise and agree as follows:

      1. The Note shall be amended and restated in the form of that certain
Revolving Credit Note attached hereto as Exhibit C, to amend the maximum
principal amount thereof to Fourteen Million Five Hundred Thousand Dollars
($14,500,000.00), and to make certain amendments as set forth therein. All
references in the Loan Agreement and the other Transaction Documents to the
"Note," the "Revolving Credit Note" and other references of similar import shall
hereafter be amended and deemed to refer to the Note in the form of the
Revolving Credit Note, as amended and restated in the form attached hereto as
Exhibit C.

      2. The third paragraph beginning with the word "WHEREAS" on the first page
of the Loan Agreement shall be deleted in its entirety and in its place shall be
substituted the following:

            WHEREAS, Borrowers, including Virbac AH and Francodex which have
      been added as parties to the credit facilities, have requested that the
      aggregate amount thereof be amended to an aggregate principal amount of up
      to Fourteen Million Five Hundred

<PAGE>

      Thousand Dollars ($14,500,000.00) and otherwise amended on the terms and
      conditions set forth herein, with such loans to mature on July 31, 2005;
      and

      3. Section 3.1(a) of the Loan Agreement shall be deleted in its entirety
and in its place shall be substituted the following:

            (a) Revolving Credit Loans. Subject to the terms and conditions
      hereof, during the Term of this Agreement, Bank hereby agrees to make such
      loans (individually, a "Loan" and collectively, the "Loans") to Borrowers,
      jointly and severally, as any of the Borrowers may from time to time
      request pursuant to Section 3.2 and in Bank's discretion, to issue Letters
      of Credit for the account of the Borrowers, or any of them, upon any
      Borrower's execution of a Letter of Credit Application therefor pursuant
      to Section 3.3 (subject to Bank's approval of the form of the Letters of
      Credit requested to be issued). The maximum aggregate principal amount of
      Loans plus the face amount of issued and outstanding Letters of Credit
      which Bank, cumulatively, may be required to have outstanding hereunder at
      any one time shall not exceed the lesser of Fourteen Million Five Hundred
      Thousand Dollars ($14,500,000.00) (the "Bank's Commitment"), or (ii) the
      Borrowing Base (as hereinafter defined). Subject to the terms and
      conditions hereof, Borrowers may jointly and severally borrow, repay and
      reborrow such sums from Bank, provided, however, that the aggregate
      principal amount of all Loans outstanding hereunder plus the face amount
      of Letters of Credit issued and outstanding hereunder at any one time
      shall not exceed the lesser of the Bank's Commitment or the then current
      Borrowing Base. The Loans may be either (a) a Prime Loan, (b) a LIBOR Loan
      or (c) any combination thereof, as determined by the Borrowers and
      notified to the Bank in accordance with Section 3.2 herein, provided,
      however, that the amount of any Loan under this Section 3.1(a) which is a
      LIBOR Loan shall be for an aggregate principal amount of at least
      $500,000.00 or any larger multiple of $100,000.00.

      4. Section 3.1(d) of the Loan Agreement shall be deleted in its entirety
and in its place shall be substituted the following:

            (d) Borrowing Base Certificate. Borrowers shall deliver to Bank on
      the twenty-eighth (28th) day of each month, commencing in the month of
      August, 2003, a borrowing base certificate in the form of Exhibit A
      attached to the Fifth Amendment to Credit Agreement dated as of August 11,
      2003 made by and among Borrowers and Banks (the "Fifth Amendment") and
      incorporated herein by reference (a "Borrowing Base Certificate") setting
      forth:

                  (i) the Borrowing Base and its components as of the end of the
      immediately preceding month;

                  (ii) the aggregate principal amount of all outstanding Loans
      and the aggregate face amount of all issued and outstanding Letters of
      Credit; and

                  (iii) the difference, if any, between the Borrowing Base and
      the aggregate principal amount of all outstanding Loans plus the aggregate
      face amount of all issued and outstanding Letters of Credit.

      The Borrowing Base shown in such Borrowing Base Certificate shall be and
      remain the Borrowing Base hereunder until the next Borrowing Base
      Certificate is delivered to Bank, at which time the Borrowing Base shall
      be the amount shown in such subsequent

                                     - 2 -
<PAGE>

      Borrowing Base Certificate. Each Borrowing Base Certificate shall be
      certified (subject to normal year-end adjustments) as to truth and
      accuracy by the President, principal financial officer or controller of
      each of the Borrowers.

All references in the Loan Agreement and the other Transaction Documents to the
"Borrowing Base Certificate" and other references of similar import shall
hereafter be amended and deemed to refer to a Borrowing Base Certificate in the
form of the Borrowing Base Certificate, as amended and restated in the form
attached hereto as Exhibit A.

      5. The last sentence of Section 3.2 of the Loan Agreement shall be deleted
in its entirety and in its place shall be substituted the following:

      Contemporaneously with the execution of the Fifth Amendment (amending this
      Agreement), Borrowers shall execute and deliver to Bank a Note of
      Borrowers dated as of August 11, 2003 and payable jointly and severally to
      the order of Bank in the original principal amount of Fourteen Million
      Five Hundred Thousand Dollars ($14,500,000.00) in the form attached as
      Exhibit C to such Fifth Amendment and incorporated herein by reference (as
      the same may from time to time be amended, modified, extended or renewed,
      the "Note").

      6. Section 7.1(i)(i) of the Loan Agreement shall be deleted in its
entirety and in its place shall be substituted the following:

            (i) Maintain a ratio of Consolidated EBITDA minus permitted
      purchases by Borrowers of any of the outstanding capital stock of Virbac
      during any such period (determined on a consolidated basis for Borrowers
      and their Consolidated Subsidiaries and in accordance with Generally
      Accepted Accounting Principles consistently applied, for the applicable
      period ending on the date of any such calculation), to Consolidated Debt
      Service of at least 3.00 to 1.0 for the four quarter period ending at each
      quarter-end and fiscal year end during the Term hereof;

      7. In consideration of Bank's agreement to amend the Loan Agreement and
Note as set forth herein, Borrowers agree to jointly and severally pay to Bank
an amendment fee in the amount of $2,500.00, which amendment fee is due and
payable on the date hereof and shall be fully earned on the date hereof.
Borrowers further jointly and severally agree to reimburse Bank, upon demand,
for all reasonable out-of-pocket costs and expenses (including reasonable legal
fees and expenses of the attorneys for the Bank) incurred by Bank in the
preparation, negotiation and execution of this Fifth Amendment to Credit
Agreement and all other documents, instruments and agreements relating to this
Fifth Amendment to Credit Agreement with the Bank.

      8. The agreements of Bank contained herein are expressly conditioned upon
deliver by Borrowers of the following:

        (a) the executed original of this Fifth Amendment to Credit Agreement;

        (b) the executed original of the amended and restated Note;

        (c) the executed original of the Eleventh Amendment to Deed of Trust and
Security Agreement;

                                     - 3 -
<PAGE>

            (d) a copy of resolutions of the Board of Directors of each of the
Borrowers, duly adopted, which authorize the execution, delivery and performance
of this Fifth Amendment to Credit Agreement and the amended and restated Note
and the other Transaction Documents, certified by the Secretary of each such
Borrower;

            (e) such other documents as Bank may reasonably request; and

            (f) payment by Borrowers of the amendment fee required under
paragraph 7 above.

      9. Borrowers hereby represent and warrant to Bank that:

            (a) The execution, delivery and performance by Borrowers of this
Fifth Amendment to Credit Agreement and the amended and restated Note are within
the corporate powers of Borrowers, have been duly authorized by all necessary
corporate action and require no action by or in respect of, or filing with, any
governmental or regulatory body, agency or official. The execution, delivery and
performance by Borrowers of this Fifth Amendment to Credit Agreement and the
amended and restated Note do not conflict with, or result in a breach of the
terms, conditions or provisions of, or constitute a default under or result in
any violation of, and none of the Borrowers is now in default under or in
violation of, the terms of the Articles of Incorporation or Bylaws of such
Borrower, any applicable law, any rule, regulation, order, writ, judgment or
decree of any court or governmental or regulatory agency or instrumentality, or
any agreement or instrument to which any of the Borrowers is a party or by which
any of them is bound or to which any of them is subject;

            (b) This Amendment to Credit Agreement and the amended and restated
Note have been duly executed and delivered and constitute the legal, valid and
binding obligations of Borrowers enforceable in accordance with their terms; and

            (c) As of the date hereof, all of the covenants, representations and
warranties of Borrowers set forth in the Loan Agreement are true and correct and
no "Event of Default" (as defined therein) under or within the meaning of the
Loan Agreement has occurred and is continuing.

      10. All references in the Loan Agreement to "this Agreement" and any other
references of similar import shall henceforth mean the Loan Agreement as amended
by this Fifth Amendment to Credit Agreement.

      11. This Fifth Amendment to Credit Agreement and the amended and restated
Note shall be binding upon and inure to the benefit of the parties hereto and
their respective successors and assigns, except that Borrowers may not assign,
transfer or delegate any of their rights or obligations hereunder.

      12. This Fifth Amendment to Credit Agreement and the amended and restated
Note shall be governed by and construed in accordance with the internal laws of
the State of Missouri.

      13. In the event of any inconsistency or conflict between this Fifth
Amendment to Credit Agreement and the Loan Agreement, the terms, provisions and
conditions of this Fifth Amendment to Credit Agreement shall govern and control.

      14. The Loan Agreement, as hereby amended and modified, and the amended
and restated Note, as hereby amended and restated, are and shall remain the
binding obligations of Borrowers and all of the provisions, terms, stipulations,
conditions, covenants and powers contained therein shall stand and remain in
full force and effect, except only as the same are herein and hereby
specifically varied or amended, and the same are hereby ratified and confirmed.
If any installment of principal or interest on

                                     - 4 -
<PAGE>

the amended and restated Note shall not be paid when due as provided in the
amended and restated Note, the holder of the amended and restated Note shall be
entitled to and may exercise all rights and remedies under the amended and
restated Note and the Loan Agreement, as amended.

      15. ORAL AGREEMENTS OR COMMITMENTS TO LOAN MONEY, EXTEND CREDIT OR TO
FOREBEAR FROM ENFORCING REPAYMENT OF A DEBT, INCLUDING PROMISES TO EXTEND OR
RENEW SUCH DEBT, ARE NOT ENFORCEABLE. TO PROTECT BORROWERS AND BANK FROM ANY
MISUNDERSTANDING OR DISAPPOINTMENT, ANY AGREEMENTS REACHED BY BORROWERS AND BANK
COVERING SUCH MATTERS ARE CONTAINED IN THE LOAN AGREEMENT, AS AMENDED BY THIS
AGREEMENT, WHICH CONSTITUTES A COMPLETE AND EXCLUSIVE STATEMENT OF THE
AGREEMENTS BETWEEN BORROWERS AND BANK EXCEPT AS BORROWERS AND BANK MAY LATER
AGREE IN WRITING TO MODIFY. THE LOAN AGREEMENT, AS AMENDED BY THIS AGREEMENT,
EMBODIES THE ENTIRE AGREEMENT AND UNDERSTANDING BETWEEN THE PARTIES HERETO AND
SUPERSEDES ALL PRIOR AGREEMENTS AND UNDERSTANDINGS (ORAL OR WRITTEN) RELATING TO
THE SUBJECT MATTER HEREOF.

      IN WITNESS WHEREOF, the parties hereto have executed this instrument as of
the date first written above on this 11 day of August, 2003.

                                        VIRBAC CORPORATION
                                        PM RESOURCES, INC.
                                        ST. JON LABORATORIES, INC.
                                        VIRBAC AH, INC.
                                        FRANCODEX LABORATORIES, INC.

                                        By: /s/ Joseph Rougraff
                                           ----------------------------------
                                            Joseph Rougraff, Chief Financial
                                            Officer

                                        FIRST BANK

                                        By: /s/ Traci L. Dodson
                                           ----------------------------------
                                            Traci L. Dodson, Vice President

                                     - 5 -
<PAGE>

                                    EXHIBIT A

                           BORROWING BASE CERTIFICATE

      This Borrowing Base Certificate is delivered pursuant to Section 3.1(d) of
that certain Credit Agreement dated September 7, 1999, by and between Virbac
Corporation, PM Resources, Inc., St. JON Laboratories, Inc., Virbac AH, Inc.,
Francodex Laboratories, Inc. and First Bank (as amended, the "Loan Agreement").
All capitalized terms used and not otherwise defined herein shall have the
respective meanings ascribed to them in the Loan Agreement.

      Borrowers hereby represent and warrant to Bank that the following
information is true and correct as of ____________, 20__:

      1.    75% of face amount of Eligible Accounts of PM Resources      $______


      2.    75% of face amount of Eligible Accounts of Virbac            $______

      3.    50% of Eligible Inventory of PM Resources, valued at the
            lower of cost or market                                      $______

      4.    50% of Eligible Inventory of Virbac, valued at the lower of
            cost or market                                               $______

      5.    Sum of Items 3 and 4 above, but not to exceed $6,000,000.00  $______

      6.    Total Borrowing Base (sum of 1, 2 and 5 above not to exceed
            $14,500,000.00)                                              $______

      Borrowers hereby further represent and warrant to Bank that the following
information is true and correct as of ______________________, 20___:

      7.    Aggregate principal amount of outstanding Loans              $______

      8.    Aggregate face amount of outstanding Letters of Credit       $______

      9.    Total Outstanding (Item 7 plus Item 8)                       $______

      10.   Borrowing Base Excess (Deficit) (Item 6 minus Item 9)
            (Negative amount represents mandatory repayment)             $______

      If Item 10 above is negative, this Borrowing Base Certificate is
accompanied by the mandatory repayment required by Section 3.1(e) of the Loan
Agreement.

                                     - 6 -
<PAGE>

      This Borrowing Base Certificate is dated the _____ day of _________, 20__.

                                    VIRBAC CORPORATION
                                    PM RESOURCES, INC.
                                    ST. JON LABORATORIES, INC.
                                    VIRBAC AH, INC.
                                    FRANCODEX LABORATORIES, INC.

                                    By: ________________________________________
                                        Joseph Rougraff, Chief Financial Officer

                                     - 7 -
<PAGE>

                                    EXHIBIT C

                              Revolving Credit Note

$14,500,000.00                                              St. Louis, Missouri
                                                               August ___, 2003

      FOR VALUE RECEIVED, on July 31, 2005 (or such subsequent anniversary
thereof as determined pursuant to Section 3.16 of the Loan Agreement
(hereinafter identified)), the undersigned, VIRBAC CORPORATION, a Delaware
corporation (formerly known as Agri-Nutrition Group Limited), PM RESOURCES,
INC., a Missouri corporation, ST. JON LABORATORIES, INC., a California
corporation, FRANCODEX LABORATORIES, INC., a Kansas corporation and VIRBAC AH,
INC., a Delaware corporation (collectively, the "Borrowers"), hereby jointly and
severally promise to pay to the order of FIRST BANK, a Missouri state banking
corporation ("Bank"), the principal sum of Fourteen Million Five Hundred
Thousand Dollars ($14,500,000.00), or such lesser sum as may then be outstanding
hereunder. The aggregate principal amount which Bank shall be committed to have
outstanding hereunder at any one time shall not exceed the lesser of (i)
Fourteen Million Five Hundred Thousand Dollars ($14,500,000.00), or (ii) the
"Borrowing Base" (as defined in the Loan Agreement (as hereinafter defined)),
which amount may be borrowed, paid, reborrowed and repaid, in whole or in part,
subject to the terms and conditions hereof and of the Loan Agreement hereinafter
identified.

      Borrowers further jointly and severally promise to pay to the order of
Bank interest on the principal amount from time to time outstanding hereunder
prior to maturity from the date disbursed until paid at the rate or rates per
annum required by the Loan Agreement or otherwise selected by any of the
Borrowers as set forth in the Loan Agreement. All accrued and unpaid interest
with respect to each principal disbursement made hereunder shall be payable on
the dates set forth in Section 3.6 of the Loan Agreement and at the maturity of
this Note, whether by reason of acceleration or otherwise. After the maturity of
this Note, whether by reason of acceleration or otherwise, interest shall accrue
and be payable on demand on the entire outstanding principal balance hereunder
until paid at a rate per annum equal to Three and One-Half Percent (3.50%) over
and above the Prime Rate, fluctuating as and when said Prime Rate shall change.
All payments hereunder (other than prepayments) shall be applied first to the
payment of all accrued and unpaid interest, with the balance, if any, to be
applied to the payment of principal. All prepayments hereunder shall be applied
solely to the payment of principal.

      All payments of principal and interest hereunder shall be made in lawful
currency of the United States in Federal or other immediately available funds at
the office of Bank situated at 135 North Meramec, Clayton, Missouri 63105, or at
such other place as the holder hereof shall designate in writing. Interest shall
be computed on an actual day, 360-day year basis.

      Bank may record the date and amount of all loans and all payments of
principal and interest hereunder in the records it maintains with respect
thereto. Bank's books and records showing the account between Bank and Borrowers
shall be admissible in evidence in any action or proceeding and shall constitute
prima facie proof of the items therein set forth.

      This Note is the Note referred to in that certain Credit Agreement dated
as of September 7, 1999 made by and between Borrowers and Bank (as the same may
from time to time be amended, the "Loan Agreement"), to which Loan Agreement
reference is hereby made for a statement of the terms and conditions upon which
the maturity of this Note may be accelerated, and for other terms and
conditions,

                                     - 8 -
<PAGE>

including prepayment, which may affect this Note. All capitalized terms used
herein and not otherwise defined shall have the meanings assigned to such terms
in the Loan Agreement.

      This Note is secured by that certain Security Agreement dated as of May
14, 1998 executed by Virbac Corporation in favor of Bank, by that certain
Security Agreement dated as of May 14, 1998 and executed by PM Resources, Inc.
in favor of Bank, by that certain Security Agreement dated as of May 14, 1998
executed by St. JON Laboratories, Inc. in favor of Bank, by that certain
Security Agreement dated as of September 7, 1999 and executed by Virbac AH, Inc.
in favor of Bank and by that certain Security Agreement dated as of September 7,
1999 executed by Francodex Laboratories, Inc. in favor of Bank (as the same may
from time to time be amended, the "Security Agreements"), to which Security
Agreements reference is hereby made for a description of the security and a
statement of the terms and conditions upon which this Note is secured.

      This Note is also secured by that certain Deed of Trust and Security
Agreement dated September 9, 1993 and executed by PM Resources, Inc. in favor of
Katherine D. Knocke, as trustee for Bank (as the same may from time to time be
amended, the "Deed of Trust"), to which Deed of Trust reference is hereby made
for a description of the security and a statement of the terms and conditions
upon which this Note is secured.

      This Note is also secured by that certain Agreement of Pledge dated as of
September 7, 1999 and executed by Virbac Corporation in favor of Bank and by
that certain Agreement of Pledge dated as of September 7, 1999 and executed by
Virbac AH, Inc. in favor of Bank (collectively, as the same may from time to
time be amended, the "Pledge Agreements"), to which Pledge Agreements reference
is hereby made for a description of the additional security and a statement of
the terms and conditions upon which this Note is further secured.

      If any of the Borrowers shall fail to make any payment of any principal of
or interest on this Note as and when the same shall become due and payable, or
if an "Event of Default" (as defined therein) shall occur under or within the
meaning of the Loan Agreement, any of the Security Agreements, the Deed of Trust
or any of the Pledge Agreements, Bank may, at its option, terminate its
obligation to make any additional loans under this Note and Bank may further
declare the entire outstanding principal balance of this Note and all accrued
and unpaid interest thereon to be immediately due and payable.

      In the event that any payment of any principal of or interest on this Note
shall not be paid when due, whether by reason of acceleration or otherwise, and
this Note shall be placed in the hands of an attorney or attorneys for
collection or for foreclosure of any of the Security Agreements, the Deed of
Trust or any of the Pledge Agreements securing payment hereof or for
representation of Bank in connection with bankruptcy or insolvency proceedings
relating hereto, Borrowers jointly and severally promise to pay, in addition to
all other amounts otherwise due hereon, the reasonable costs and expenses of
such collection, foreclosure and representation, including, without limitation,
reasonable attorneys' fees and expenses (whether or not litigation shall be
commenced in aid thereof). All parties hereto severally waive presentment for
payment, demand, protest, notice of protest and notice of dishonor.

                                     - 9 -
<PAGE>

      This Note shall be governed by and construed in accordance with the
internal laws of the State of Missouri.

      This Revolving Credit Note is a renewal, restatement and continuation of
the obligations due Bank as evidenced by a Revolving Credit Note dated August 7,
2002 from Borrower payable to the order of Bank in the maximum principal amount
of $12,000,000.00 (the "Prior Note"), and is not a novation thereof. All
interest evidenced by the Prior Note being amended and restated by this
instrument shall continue to be due and payable until paid.

                                   VIRBAC CORPORATION

                                   By: /s/ Joseph Rougraff
                                      -----------------------------------------
                                       Joseph Rougraff, Chief Financial Officer

                                   PM RESOURCES, INC.

                                   By: /s/ Joseph Rougraff
                                      -----------------------------------------
                                       Joseph Rougraff, Chief Financial Officer

                                   ST. JON LABORATORIES, INC.

                                   By: /s/ Joseph Rougraff
                                      -----------------------------------------
                                       Joseph Rougraff, Chief Financial Officer

                                   VIRBAC AH, INC.

                                   By: /s/ Joseph Rougraff
                                      -----------------------------------------
                                       Joseph Rougraff, Chief Financial Officer

                                   FRANCODEX LABORATORIES, INC.

                                   By: /s/ Joseph Rougraff
                                      -----------------------------------------
                                       Joseph Rougraff, Chief Financial Officer

                                     - 10 -