<PAGE>
 
                                                            Exhibit 3(b)

                                AMENDED BYLAWS
                                      OF
                                 VETLINE, INC.

                                 May 29, 1986
<PAGE>
 
                                   ARTICLE I
                                   ---------

     1.1  Business Office.  The principal office and place of business of the
          ---------------                                                    
corporation shall be in the State of Colorado at 425 John Deere Road, Fort,
Collins, Denver, Colorado 80524. Other offices and places of business may be
established from time to time by resolution of the Board of Directors or as the
business of the corporation may require.

     1.2  Registered Office.  The registered office of the corporation, required
          -----------------                                                     
by the Colorado Corporation Code to be maintained in the State of Colorado, may
be, but need not be, identical with the principal office of the Corporation in
the State of Colorado, if any, and the address of the registered office may be
changed from time to time by the Board of Directors.

                                  ARTICLE II
                                  ----------
                          SHARES AND TRANSFER THEREOF
                          ---------------------------

     2.1  Regulation.  The Board of Directors may make such rules and
          ----------                                                 
regulations as it may deem appropriate concerning the issuance, transfer and
registration of certificates for shares of the corporation, including the
appointment of transfer agents and registrars.

     2.2  Certificates for Shares.  Certificates representing shares of the
          -----------------------                                          
corporation shall be respectively numbered serially for each class of shares, or
series thereof, as they are issued, shall be impressed with the corporate seal
or a facsimile thereof, and shall be signed by the Chairman or Vice-Chairman of
the Board of Directors or by the President or a Vice-President and by the
Treasurer or an Assistant Treasurer or by the Secretary or an Assistant
Secretary; provided that such signatures may be a facsimile if the certificate
is countersigned by a transfer agent, or registered by a registrar other than
the corporation itself or its employee.  Each certificate shall state upon the
face thereof the name of the corporation, the fact that the corporation is
organized or incorporated under the laws of the State of Colorado, the name of
the person to whom issued, the date of issue, the class (or series of any
class), the number of shares represented thereby and the par value of the shares
represented thereby or a statement that such shares are without par value.  If
the corporation is authorized to issue more than one class of shares, a full
statement of the designations, preferences,  qualifications, limitations,
restrictions  and special or relative rights of the shares of each class (and
series thereof) shall be set forth on the face or back of the certificates which
the corporation shall issue, or in lieu thereof, the certificate may set forth
that such a statement or summary will be furnished to any shareholder upon
request without charge.  Each certificate shall be otherwise in such form as may
be prescribed by the Board of Directors and as shall conform to the rules of any
stock exchange on which the shares may be listed.

     The corporation shall not issue certificates representing fractional shares
and shall not be obligated to make any transfers creating a fractional interest
in a share of stock. The corporation may, but shall not be obligated to, issue
scrip in lieu of any fractional shares, such scrip to have terms and conditions
specified by the Board of Directors.

                                      -1-
<PAGE>
 
     2.3  Cancellation of Certificates.   All  certificates surrendered to the
          ----------------------------                                        
corporation for transfer shall be cancelled and no new certificates shall be
issued in lieu thereof until the former certificate for a like number of shares
shall have been surrendered and cancelled, except as herein provided with
respect to lost, stolen or destroyed certificates.

     2.4  Lost, Stolen or Destroyed Certificates.  Any shareholder claiming
          --------------------------------------                           
that his certificate for shares is lost, stolen or destroyed may make an
affidavit or affirmation of the fact and lodge the same with the Secretary of
the corporation, accompanied by a signed application for a new certificate.
Thereupon, and upon the giving of a satisfactory bond of indemnity to the
corporation not exceeding an amount double the value of the shares as
represented by such certificate (the necessity for such bond and the amount
required to be determined by the President and Treasurer of the corporation), a
new certificate may be issued of the same tenor and representing the same
number, class and series of shares as were represented by the certificate
alleged to be lost, stolen or destroyed.

     2.5  Transfer of Shares.  Subject to the terms of any shareholder agreement
          ------------------                                                    
relating to the transfer of shares or other transfer restrictions contained in
the Articles of Incorporation or authorized therein, shares of the corporation
shall be transferable on the books of the corporation by the holder thereof in
person or by his duly authorized attorney, upon the surrender and cancellation
of a certificate or certificates for a like number of shares.  Upon presentation
and surrender of a certificate for shares properly endorsed and payment of all
taxes therefor, the transferee shall be entitled to a new certificate or
certificates in lieu thereof.  As against the corporation, a transfer of shares
can be made only on the books of the corporation and in the manner hereinabove
provided, and the corporation shall be entitled to treat the holder of record of
any share as the owner thereof and shall not be bound to recognize any equitable
or other claim to or interest in such share on the part of any other person,
whether or not it shall have express or other notice thereof, save as expressly
provided by the statutes of the State of Colorado.

     2.6  Transfer Agent.  Unless otherwise specified by the Board of Directors
          --------------                                                       
by resolution, the Secretary of the corporation shall act as transfer agent of
the certificates representing the shares of stock of the corporation.  He shall
maintain a stock transfer book, the stubs in which shall set forth among other
things, the names and addresses of the holders of all issued shares of the
corporation, the number of shares held by each, the certificate numbers
representing such shares, the date of issue of the certificates representing
such shares, and whether or not such shares originate from original issue or
from transfer.  Subject to Section 3.7, the names and addresses of the
shareholders as they appear on the stubs of the stock transfer book shall be
conclusive evidence as to who are the shareholders of record and as such
entitled to receive notice of the meetings of shareholders; to vote at such
meetings; to examine the list of the shareholders entitled to vote at meetings;
to receive dividends; and to own, enjoy and exercise any other property or
rights deriving from such shares against the corporation.  Each shareholder
shall be responsible for notifying the Secretary in writing of any change in his
name or address and failure so to do will relieve the corporation, its
directors, officers and agents, from liability for failure to direct notices or
other documents, or pay over or transfer dividends or other property or rights,
to a name or address other than the name and address appearing on the stub of
the stock transfer book.

                                      -2-
<PAGE>
 
     2.7  Close of Transfer Book and Record Date.  For the purpose of
          --------------------------------------                     
determining shareholders entitled to notice of or to vote at any meeting of
shareholders, or any adjournment thereof, or entitled to receive payment of any
dividend, or in order to make a determination of shareholders for any other
proper purpose, the Board of Directors may provide that the stock transfer books
shall be closed for a stated period, but not to exceed, in any case, fifty days.
If the stock transfer books shall be closed for the purpose of determining
shareholders entitled to notice of, or to vote at a meeting of shareholders,
such books shall be closed for at least ten days immediately preceding such
meeting. In lieu of closing the stock transfer books, the Board of Directors may
fix in advance a date as the record date for any such determination of
shareholders, such date in any case to be not more than fifty days and, in case
of a meeting of shareholders, not less than ten days prior to the date on which
the particular action requiring such determination of shareholders is to be
taken. If the stock transfer books are not closed and no record date is fixed
for the determination of shareholders entitled to notice of or to vote at a
meeting of shareholders, or shareholders entitled to receive payment of a
dividend, the date on which notice of the meeting is mailed or the date on which
the resolution of the Board of Directors declaring such dividend is adopted, as
the case may be, shall be the record date for such determination of
shareholders.  When a determination of shareholders entitled to vote at any
meeting of shareholders has been made as provided in this section, such
determination shall apply to any adjournment thereof.

                                  ARTICLE III
                                  -----------
                       SHAREHOLDERS AND MEETINGS THEREOF
                       ---------------------------------

     3.1  Shareholders of Record.   Only shareholders of record on the books of
          ----------------------                                               
the corporation shall be entitled to be treated by the corporation as holders in
fact of the shares standing in their respective names, and the corporation shall
not be bound to recognize any equitable or other claim to, or interest in, any
shares on the part of any other person, firm or corporation, whether or not it
shall have express or other notice thereof, except as expressly provided by the
laws of Colorado.

     3.2  Meetings.  Meetings of shareholders shall be held at the principal
          --------                                                          
office of the corporation, or at such other place as specified from time to time
by the Board of~Directors. If the Board of Directors shall specify another
location such change in location shall be recorded on the notice calling such
meeting.

     3.3  Annual Meeting.  In the absence of a resolution of the Board of
          --------------                                                 
Directors providing otherwise, the annual meeting of shareholders of the
corporation for the election of directors, and for the transaction of such other
business as may properly come before the meeting, shall be held on the first
Tuesday of the fifth month in each fiscal year, if the same be not a legal
holiday, and if a legal holiday in the State of Colorado, then on the next
succeeding business day, at 9:00 o'clock a.m.  If the election of Directors
shall not be held on the day designated herein for any annual meeting of the
shareholders, the Board of Directors shall cause the election to be held at a
special meeting of the shareholders as soon thereafter as may be convenient.  If
the annual meeting is not held within any thirteen month period, any court of
competent jurisdiction in the State of Colorado may, on the application of any
shareholder, summarily order a meeting to be held.

                                      -3-
<PAGE>
 
     3.4  Special Meetings.   Special meetings of shareholders, for any
          ----------------                                             
purpose or purposes, unless otherwise prescribed by statute, may be called by
the President, the Board of Directors, the holders of not less than one-tenth of
all the shares entitled to vote at the meeting, or legal counsel of the
corporation as last designated by resolution of the Board of Directors.

     3.5  Notice.  Written notice stating the place, day and hour of the meeting
          ------
and, in case of a special meeting, the purpose or purposes for which the meeting
is called, shall be delivered unless otherwise prescribed by statute not less
than ten days nor more than fifty days before the date of the meeting, either
personally or by mail, by or at the direction of the President, the Secretary,
or the officer or person calling the meeting to each shareholder of record
entitled to vote at such meeting; except that, if the authorized shares are to
be increased, at least thirty days' notice shall be given, and if the sale of
all or substantially all of the corporation's assets is to be voted upon, at
least twenty days' notice shall be given. Any shareholder may waive notice of
any meeting.

     Notice to shareholders of record, if mailed, shall be deemed given as to
any shareholder of record, when deposited in the United States mail, addressed
to the shareholder at his address as it appears on the stock transfer books of
the corporation, with postage thereon prepaid, but if three successive letters
mailed to the last-known address of any shareholder of record are returned as
undeliverable, no further notices to such shareholder shall be necessary, until
another address for such shareholder is made known to the corporation.

     3.6  Waiver of Notice.  When any notice is required to be given to any
          ----------------                                                 
shareholder of the corporation under the provisions of Colorado Law or under the
provisions of the Articles of Incorporation of the corporation or these Bylaws,
a waiver thereof in writing signed by the person entitled to such notice,
whether before, at, or after the time stated therein, shall be equivalent to the
giving of such notice.

     3.7  Voting Record.  The officer or agent having charge of the stock
          -------------                                                  
transfer books for shares of the corporation shall make, at least ten days
before such meeting of shareholders, a complete record of the shareholders
entitled to vote at each meeting of shareholders or any adjournment thereof,
arranged in alphabetical order, with the address of and the number of shares
held by each.  The record, for a period of ten days prior to such meeting, shall
be kept on file at the principal office of the corporation, whether within or
without the State of Colorado, and shall be subject to inspection by any
shareholder for any purpose germane to the meeting at any time during usual
business hours. Such record shall be produced and kept open at the time and
place of the meeting and shall be subject to the inspection of any shareholder
during the whole time of the meeting for the purposes thereof.

     The original stock transfer books shall be the prima facie evidence as to
who are the shareholders entitled to examine the record or transfer books or to
vote at any meeting of shareholders.

     An officer or agent having charge of the stock transfer books who fails to
prepare the record 

                                      -4-
<PAGE>
 
of shareholders, or keep it on file for a period of ten days before the meeting
or produce and keep it open for inspection at the meeting, as provided in this
section, is liable to any shareholder suffering damage on account of such
failure to the extent of such damage.

     3.8  Quorum.  One-third of the outstanding shares of the corporation
          ------                                                         
entitled to vote, represented in person or by proxy, shall constitute a quorum
at any meeting of shareholders, except as otherwise provided by the Colorado
Corporation Code and the Articles of Incorporation.  In the absence of a quorum
at any such meeting, a majority of the shares so represented may adjourn the
meeting from time to time for a period not to exceed sixty days without further
notice.  At such adjourned meeting at which a quorum shall be present or
represented, any business may be transacted which might have been transacted at
the meeting as originally noticed.  The shareholders present at a duly organized
meeting may continue to transact business until adjournment, notwithstanding the
withdrawal of enough shareholders to leave less than a quorum.

     3.9  Manner of Acting.  If a quorum is present, the affirmative vote of the
          ----------------
majority of the shares represented at the meeting and entitled to vote on the
subject matter shall be the act of the shareholders, unless the vote of a
greater proportion or number or voting by classes is otherwise required by
statute or by the Articles of Incorporation or these Bylaws.

     3.10 Proxies.  At all meetings of shareholders a shareholder may vote in
          -------
person or by proxy executed in writing by the shareholder or by his duly
authorized attorney-in-fact. Such proxy shall be filed with the Secretary of the
corporation before or at the time of the meeting. No proxy shall be valid after
eleven months from the date of its execution, unless otherwise provided in the
proxy.

     3.11 Voting of Shares.  Unless otherwise provided by these Bylaws or the
          ----------------
Articles of Incorporation, each outstanding share entitled to vote shall be
entitled to one vote upon each matter submitted to a vote at a meeting of
shareholders, and each fractional share shall be entitled to a corresponding
fractional vote on each such matter.

     3.12 Voting of Shares by Certain Holders.   Shares standing in the name of
          ------------------------------------
another corporation may be voted by such officer, agent or proxy as the bylaws
of such corporation may prescribe, or, in the absence of such provision, as the
Board of Directors of such other corporation may determine.

     Shares standing in the name of a deceased person, a minor ward or an
incompetent person, may be voted by his administrator, executor, court appointed
guardian or conservator, either in person or by proxy without a transfer of such
shares into the name of such administrator, executor, court appointed guardian
or conservator.  Shares standing in the name of a trustee may be voted by him,
either in person or by proxy, but no trustee shall be entitled to vote shares
held by him without a transfer of such shares into his name.

     Shares standing in the name of a receiver may be voted by such receiver,
and shares held by or under the control of a receiver may be voted by such
receiver without the transfer thereof into his 

                                      -5-
<PAGE>
 
name if authority so to do be contained in an appropriate order of the court by
which such receiver was appointed.

     A shareholder whose shares are pledged shall be entitled to vote such
shares until the shares have been transferred into the name of the pledgee, and
thereafter the pledgee shall be entitled to vote the shares so transferred.

     Neither shares of its own stock belonging to this corporation, nor shares
of its own stock held by it in a fiduciary capacity, nor shares of its own stock
held by another corporation if the majority of shares entitled to vote for the
election of directors of such corporation is held by this corporation may be
voted, directly or indirectly, at any meeting and shall not be counted in
determining the total number of outstanding shares at any given time.

     Redeemable shares which have been called for redemption shall not be
entitled to vote on any matter and shall not be deemed outstanding shares on and
after the date on which written notice of redemption has been mailed to
shareholders and a sum sufficient to redeem such shares has been deposited with
a bank or trust company with irrevocable instruction and authority to pay the
redemption price to the holders of the shares upon surrender of certificates
therefor.

     3.13 Informal Action by Shareholders.  Any action required or permitted to
          -------------------------------                                      
be taken at a meeting of the shareholders may be taken without a meeting if a
consent in writing, setting forth the action so taken, shall be signed by all of
the shareholders entitled to vote with respect to the subject matter thereof.

     3.14 Voting by Ballot.  Voting on any question or in any election may be
          ----------------                                                   
by voice vote unless the presiding officer shall order or any shareholder shall
demand that voting be by ballot.

     3.15 Cumulative Voting.  No shareholder shall be permitted to cumulate his
          -----------------                                                    
votes by giving one candidate as many votes as the number of such directors
multiplied by the number of his shares shall equal, or by distributing such
votes on the same principal among any number of candidates.

                                  ARTICLE IV
                                  ----------
                        DIRECTORS, POWERS AND MEETINGS
                        ------------------------------

     4.1  Board of Directors.  The business and affairs of the corporation
shall be managed by a board of from three (3) to nine (9) directors who need not
be shareholders of the corporation or residents of the State of Colorado and who
shall be elected at the annual meeting of shareholders or some adjournment
thereof. Directors shall hold office until the next succeeding annual meeting of
shareholders and until their successors shall have been elected and shall
qualify. The Board of Directors may increase or decrease, to not less than
three, the number of directors by resolution; except that there need only be as
many directors as there are shareholders in the event that the outstanding
shares are held of record by fewer than three shareholders.

                                      -6-
<PAGE>
 
     4.2  Regular Meetings.  A regular, annual meeting of the Board of Directors
          ----------------                                                      
shall be held at the same place as, and immediately after, the annual meeting of
shareholders, and no notice shall be required in connection therewith.  The
annual meeting of the Board of Directors shall be for the purpose of electing
officers and the transaction of such other business as may come before the
meeting.  The Board of Directors may provide, by resolution, the time and place,
either within or without the State of Colorado, for the holding of additional
regular meetings without other notice than such resolution.

     4.3  Special Meetings.  Special meetings of the Board of Directors may
          ----------------                                                 
be called by or at the request of the President or any two directors.  The
person or persons authorized to call special meetings of the Board of Directors
may fix any place, either within or without the State of Colorado, as the place
for holding any special meeting of the Board of Directors called by them.

     4.4  Notice.  Written notice of any special meeting of directors shall
          ------                                                           
be given as follows:

          (a)  By mail to each director at his business address at least three
days prior to the meeting; or

          (b)  By personal delivery or telegram at least twenty-four hours prior
to the meeting to the business address of each director, or in the event such
notice is given on a Saturday, Sunday or holiday, to the residence address of
each director.  If mailed, such notice shall be deemed to be delivered when
deposited in the United States mail, so addressed, with postage thereon prepaid.
If notice be given by telegram, such notice shall be deemed to be delivered when
the telegram is delivered to the telegraph company. Any director may waive
notice of any meeting.  The attendance of a director at any meeting shall
constitute a waiver of notice of such meeting, except where a director attends a
meeting for the express purpose of objecting to the transaction of any business
because the meeting is not lawfully called or convened.  Neither the business to
be transacted at, nor the purpose of, any regular or special meeting of the
Board of Directors need be specified in the notice or waiver of notice of such
meeting.

     4.5  Participation by Electronic Means.  Except as may be otherwise
          ---------------------------------                             
provided by the Articles of Incorporation or Bylaws, members of the Board of
Directors or any committee designated by such Board may participate in a meeting
of the Board or committee by means of conference telephone or similar
communications equipment by which all persons participating in the meeting can
hear each other at the same time.  Such participation shall constitute presence
in person at the meeting.

     4.6  Quorum and Manner of Acting.  A quorum at all meetings of the Board of
          ---------------------------                                           
Directors shall consist of a majority of the number of directors then holding
office, but a smaller number may adjourn from time to time without further
notice, until a quorum is secured.  The act of the majority of the directors
present at a meeting at which a quorum is present shall be the act of the Board
of Directors, unless the act of a greater number is required by the laws of the
State of Colorado or by the Articles of Incorporation or these Bylaws.

                                      -7-
<PAGE>
 
     4.7  Organization.  The Board of Directors shall elect a chairman to
          ------------                                                   
preside at each meeting of the Board of Directors. The Board of Directors shall
elect a Secretary to record the discussions and resolutions of each meeting.

     4.8  Presumption of Assent.  A director of the corporation who is present
          ---------------------                                               
at a meeting of the Board of Directors at which action on any corporate matter
is taken shall be presumed to have assented to the action taken unless his
dissent shall be entered in the minutes of the meeting or unless he shall file
his written dissent to such action with the person acting as the Secretary of
the meeting before the adjournment thereof or shall forward such dissent by
registered mail to the Secretary of the corporation immediately after the
adjournment of the meeting. Such right to dissent shall not apply to a director
who voted in favor of such action.

     4.9  Informal Action By Directors.  Any action required or permitted to be
          ----------------------------                                         
taken by the Board of Directors, or a committee thereof, at a meeting may be
taken without a meeting if a consent in writing, setting forth the action so
taken, shall be signed by all the directors or all the committee members
entitled to vote with respect to the subject matter thereof.

     4.10 Vacancies.  Any vacancy occurring in the Board of Directors may be
          ---------                                                         
filled by the affirmative vote of a majority of the remaining directors though
less than a quorum of the Board of Directors.  A director elected to fill a
vacancy shall be elected for the unexpired term of his predecessor in office,
and shall hold such office until his successor is duly elected and shall
qualify. Any directorship to be filled by reason of an increase in the number of
directors shall be filled by the affirmative vote of a majority of the directors
then in office or by an election at an annual meeting, or at a special meeting
of shareholders called for that purpose.  A director chosen to fill a position
resulting from an increase in the number of directors shall hold office only
until the next election of directors by the shareholders.

     4.11 Compensation.  By resolution of the Board of Directors and
          ------------                                              
irrespective of any personal interest of any of the members, each director may
be paid his expenses, if any, of attendance at each meeting of the Board of
Directors, and may be paid a stated salary as director or a fixed sum for
attendance at each meeting of the Board of Directors or both.  No such payment
shall preclude any director from serving the corporation in any other capacity
and receiving compensation therefor.

     4.12 Removal of Directors.  Any director or directors of the corporation
          --------------------                                               
may be removed at any time, with or without cause, in the manner provided in the
Colorado Corporation Code.

     4.13 Resignations.  A director of the corporation may resign at any time
          ------------                                                       
by giving written notice to the Board of Directors, President or Secretary of
the corporation.  The resignation shall take effect upon the date of receipt of
such notice, or at any later period of time specified therein.  The acceptance
of such resignation shall not be necessary to make it effective, unless the
resignation requires it to be effective as such.

     4.14 General Powers.  The business and affairs of the corporation shall be
          --------------                                                       
managed by the

                                      -8-
<PAGE>
 
Board of Directors which may exercise all such powers of the corporation and do
all such lawful acts and things as are not by statute or by the Articles of
Incorporation or by these Bylaws directed or required to be exercised or done by
the shareholders. The directors shall pass upon any and all bills or claims of
officers for salaries or other compensation and, if deemed advisable, shall
contract with officers, employees, directors, attorneys, accountants, and other
persons to render services to the corporation.

                                   ARTICLE V
                                   ---------
                                   OFFICERS
                                   --------

     5.1  Term and Compensation.  The elective officers of the corporation shall
          ---------------------                                                 
consist of at least a President, a Secretary and a Treasurer each of whom shall
be eighteen years or older and who shall be elected by the Board of Directors at
its annual meeting.  Unless removed in accordance with procedures established by
law and these Bylaws, the said officers shall serve until the next succeeding
annual meeting of the Board of Directors and until their respective successors
are elected and shall qualify. Any two officers, but not more than two, may be
held by the same person at the same time, except that one person may not
simultaneously hold the offices of President and Secretary.  The Board may elect
or appoint such other officers and agents as it may deem advisable, who shall
hold office during the pleasure of the Board.

     5.2  Powers.  Unless otherwise established by the Board of Directors, the
          ------                                                              
officers of the corporation shall exercise and perform the respective powers,
duties and functions as are stated below, and as may be assigned to them by the
Board of Directors.

          (a)  The President shall be the chief executive officer of the
corporation and shall, subject to the control of the Board of Directors, have
general supervision, direction and control of the business and officers of the
corporation. He shall preside, when present, at all meetings of the shareholders
and of the Board of Directors unless a different chairman of such meetings is
elected by the Board of Directors.
 
          (b)  In the absence or disability of the President, the Vice President
or Vice-Presidents, if any, in order of their rank as fixed by the Board of
Directors, and if not ranked, the Vice-Presidents in the order designated by the
Board of Directors, shall perform all the duties of the President, and when so
acting shall have all the powers of, and be subject to all the restrictions on
the President.  Each Vice President shall have such other powers and perform
such other duties as may from time to time be assigned to him by the President
or the Board of Directors.

          (c)  The Secretary shall keep accurate minutes of all meetings of the
shareholders and the Board of Directors unless a different Secretary of such
meetings is elected by the Board of Directors.  He shall keep, or cause to be
kept, a record of the shareholders of the corporation and shall be responsible
for the giving of notice of meetings of the shareholders or the Board of
Directors. The Secretary shall be custodian of the records and of the seal of
the corporation and shall attest the affixing of the seal of the corporation
when so authorized.  The Secretary or Assistant Secretary shall sign all stock
certificates.  The Secretary shall perform all duties commonly incident to his
office and

                                      -9-
<PAGE>
 
such other duties as may from time to time be assigned to him by the President
or the Board of Directors.

          (d)  An Assistant Secretary may, at the request of the Secretary, or
in the absence or disability of the Secretary, perform all of the duties of the
Secretary. He shall perform such other duties as may be assigned to him by the
President or by the Secretary.

          (e)  The Treasurer, subject to the order of the Board of Directors,
shall have the care and custody of the money, funds, valuable papers and
documents of the corporation.  He shall keep accurate books of accounts of the
corporation's transactions, which shall be the property of the corporation, and
shall render financial reports and statements of condition of the corporation
when so requested by the Board of Directors or President.  The Treasurer shall
perform all duties commonly incident to his office and such other duties as may
from time to time be assigned to him by the President or the Board of Directors.
In the absence or disability of the President and Vice-President or Vice
Presidents, the Treasurer shall perform the duties of the President.

          (f)  An Assistant Treasurer may, at the request of the Treasurer, or
in the absence or disability of the Treasurer, perform all of the duties of the
Treasurer.  He shall perform such other duties as may be assigned to him by the
President or by the Treasurer.

     5.3  Compensation.  All officers of the corporation may receive salaries or
          -------------                                              
other compensation if so ordered and fixed by the Board of Directors. The board
shall have authority to fix salaries in advance for stated periods or render the
same retroactive as the Board may deem advisable.

     5.4  Delegation of Duties.  In the event of absence or inability of any
          --------------------                                          
officer to act, the Board of Directors may delegate the powers or duties of such
officer to any other officer, director or person whom it may select.

     5.5  Bonds.  If the Board of Directors by resolution shall so require,
          -----                                                            
any officer or agent of the corporation shall give bond to the corporation in
such amount and with such surety as the Board of Directors may deem sufficient,
conditioned upon the faithful performance of their respective duties and
offices.

     5.6  Removal.  Any officer or agent may be removed by the Board of
          -------                                                      
Directors or by the executive committee, if any, whenever in its judgment the
best interest of the corporation will be served thereby, but such removal shall
be without prejudice to the contract rights, if any, of the person so removed.
Election or appointment of an officer or agent shall not, of itself, create
contract rights.

                                  ARTICLE VI
                                  ----------
                                    FINANCE
                                    -------

                                     -10-
<PAGE>
 
     6.1  Reserve Funds.  The Board of Directors, in its uncontrolled
          -------------                                              
discretion, may set aside from time to time, out of the net profits or earned
surplus of the corporation, such sum or sums as it deems expedient as a reserve
fund to meet contingencies, for equalizing dividends, for maintaining any
property of the corporation, and for any other purpose.

     6.2  Banking.  The moneys of the corporation shall be deposited in the
          -------                                                          
name of the corporation in such bank or banks or trust company or trust
companies, as the Board of Directors shall designate, and may be drawn out only
on checks signed in the name of the corporation by such person or persons as the
Board of Directors, by appropriate resolution, may direct. Notes and commercial
paper, when authorized by the Board, shall be signed in the name of the
corporation by such officer or officers or agent or agents as shall thereunto be
authorized from time to time.

                                  ARTICLE VII
                                   DIVIDENDS

     Subject to the provisions of the Articles of Incorporation and the laws of
the State of Colorado, the Board of Directors may declare dividends whenever,
and in such amounts, as in the Board's opinion the condition of the affairs of
the corporation shall render such advisable.

                                 ARTICLE VIII
                                 ------------
                          CONTRACTS, LOANS AND CHECKS
                          ---------------------------

     8.1  Execution of Contracts.  Except as otherwise provided by statute
          ----------------------                                          
or by these Bylaws, the Board of Directors may authorize any officer or agent of
the corporation to enter into any contract, or execute and deliver any
instrument in the name of, and on behalf of the corporation. Such authority may
be general or confined to specific instances and, unless so authorized, no
officer, agent or employee shall have any power to bind the corporation for any
purpose, except as may be necessary to enable the corporation to carry on its
normal and ordinary course of business.

     8.2  Loans.  No loans shall be contracted on behalf of the corporation and
          -----                                                                
no negotiable paper shall be issued in its name unless authorized by the Board
of Directors.  When so authorized, any officer or agent of the corporation may
effect loans and advances at any time for the corporation from any bank, trust
company or institution, firm, corporation or individual. An agent so authorized
may make and deliver promissory notes or other evidence of indebtedness of the
corporation and may mortgage, pledge, hypothecate or transfer any real or
personal property held by the corporation as security for the payment of such
loans.   Such authority,  in the Board of Directors' discretion, may be general
or confined to specific instances.

     8.3  Checks.  Checks, notes, drafts and demands for money or other evidence
          ------                                                                
of indebtedness issued in the name of the corporation shall be signed by such
person or persons as designated by the Board of Directors and in the manner the
Board of Directors prescribes.

                                     -11-
<PAGE>
 
     8.4  Deposits.  All funds of the corporation not otherwise employed shall
          --------                                                            
be deposited from time to time to the credit of the corporation in such banks,
trust companies or other depositories as the Board of Directors may select.

                                  ARTICLE IX
                                  ----------
                                  FISCAL YEAR
                                  -----------

     The fiscal year of the corporation shall be the year adopted by resolution
of the Board of Directors.

                                   ARTICLE X
                                   ---------
                                CORPORATE SEAL
                                --------------

     The Board of Directors shall provide a corporate seal which shall be
circular in form and shall have inscribed thereon the name of the corporation
and the state of incorporation and the words "CORPORATE SEAL".

                                  ARTICLE XI
                                  ----------
                                  AMENDMENTS
                                  ----------

     Subject to repeal or change by action of the shareholders, these Bylaws may
be altered, amended or repealed and new Bylaws may be adopted by a majority of
the Directors present at any meeting of the Board of Directors of the
corporation at which a quorum is present.

                                  ARTICLE XII
                                  -----------
                              EXECUTIVE COMMITTEE
                              -------------------

     12.1 Appointment.  The Board of Directors, by resolution adopted by a
          -----------                                                     
majority of the full Board, may designate from among its members an executive
committee.  The designation of such committee and the delegation thereto of
authority shall not operate to relieve the Board of Directors, or any member
thereof, of any responsibility imposed by law.

     12.2 Authority.  The executive committee, when the Board of Directors is
          ---------                                                          
not in session, shall have and may exercise all of the authority of the Board of
Directors except to the extent, if any, that such authority shall be limited by
the resolution appointing the executive committee and except also that the
executive committee shall not have the authority of the Board of Directors in
reference to declaring dividends and distributions, amending the Articles of
Incorporation, adopting a plan of merger or consolidation, filling vacancies on
the Board of Directors or any committee thereof, recommending to the
shareholders the sale, lease or other disposition of all or substantially all of
the property and assets of the corporation otherwise than in the usual and
regular course of its business, recommending to the shareholders a voluntary
dissolution of the corporation or a revocation thereof, authorize or approve the
issuance or reacquisition of shares, or amending the Bylaws of the corporation.

                                     -12-
<PAGE>
 
     12.3 Tenure and Qualifications.  Each member of the executive committee
          -------------------------                                         
shall hold office until the next regular annual meeting of the Board of
Directors following his designation.

     12.4 Meetings.  Regular meetings of the executive committee may be held
          --------                                                          
without notice at such time and places as the executive committee may fix from
time to time by resolution. Special meetings of the executive committee may be
called by any member thereof upon not less than one day's notice stating the
place, date and hour of the meeting, which notice may be written or oral, and if
mailed, shall be deemed to be delivered two days after deposited in the United
States mail addressed to the member of the executive committee at his business
address.  Any member of the executive committee may waive notice of any meeting
and no notice of any meeting need be given to any member thereof who attends in
person.  The notice of a meeting of the executive committee need not state the
business proposed to be transacted at the meeting.

     12.5 Quorum.  A majority of the members of the executive committee shall
          ------                                                             
constitute a quorum for the transaction of business at any meeting thereof, and
action of the executive committee must be authorized by the affirmative vote of
a majority of the members present at a meeting at which a quorum is present.

     12.6 Informal Action by Executive Committee.   Any action required or
          --------------------------------------                          
permitted to be taken by the executive committee at a meeting may be taken
without a meeting if a consent in writing, setting forth the action so taken,
shall be signed by all of the members of the committee entitled to vote with
respect to the subject matter thereof.

     12.7 Vacancies.  Any vacancy in the executive committee may be filled by a
          ---------                                                            
resolution adopted by a majority of the full Board of Directors.

     12.8 Resignations and Removal.  Any member of the executive committee may
          ------------------------                                            
be removed at any time with or without cause by resolution adopted by a majority
of the full Board of Directors. Any member of the executive committee may resign
from the executive committee at any time by giving written notice to the
President or Secretary of the corporation, and unless otherwise specified
therein, the acceptance of such resignation shall not be necessary to make it
effective.

     12.9 Procedure.  The executive committee shall elect a presiding
          -----------                                                  
officer from its members and may fix its own rules of procedure which shall not
be inconsistent with these Bylaws.  It shall keep regular minutes of its
proceedings and report the same to the Board of Directors for its information at
the meeting thereof held next after the proceedings shall have been taken.

                                 ARTICLE XIII
                                 ------------
                               EMERGENCY BYLAWS
                               ----------------

     The Emergency Bylaws provided in this Article shall be operative during any
emergency in the conduct of the business of the corporation resulting from an
attack on the United States or any nuclear or atomic disaster, notwithstanding
any different provision in the preceding articles of these

                                     -13-
<PAGE>
 
Bylaws or in the Articles of Incorporation of the corporation or in the Colorado
Corporation Code. To the extent not inconsistent with the provisions of this
Article, the Bylaws provided in the preceding articles shall remain in effect
during such emergency and upon its termination the Emergency Bylaws shall cease
to be operative. During any such emergency:

     (a)  A meeting of the Board of Directors may be called by any officer or
director of the corporation.  Notice of the time and place of the meeting shall
be given by the person calling the meeting to such of the directors as it may be
feasible to reach by any available means of communication.  Such notice shall
be given at such time in advance of the meeting as circumstances permit in the
judgment of the person calling the meeting.

     (b)  At any such meeting of the Board of Directors, a quorum shall consist
of the number of directors in attendance at such meeting.

     (c)  The Board of Directors, either before or during any such emergency,
may, effective in the emergency, change the principal office or designate
several alternative principal offices or regional offices, or authorize the
officers so to do.

     (d)  The Board of Directors, either before or during any such emergency,
may provide, and from time to time modify, lines of succession in the event that
during such an emergency any or all officers or agents of the corporation shall
for any reason be rendered incapable of discharging their duties.

     (e)  No officer, director or employee acting in accordance with these
Emergency Bylaws shall be liable except for willful misconduct.

     (f)  These Emergency Bylaws shall be subject to repeal or change by further
action of the Board of Directors or by action of the shareholders, but no such
repeal or change shall modify the provisions of the next preceding paragraph
with regard to action taken prior to the time of such repeal or change.  Any
amendment of these Emergency Bylaws may make any further or different provision
that may be practical and necessary for the circumstances of the emergency.

                                  CERTIFICATE
                                  -----------

     I hereby certify that the foregoing Amended Bylaws, consisting of 22 pages,
including this page, constitute the Bylaws of Vetline, Inc. adopted by the Board
of Directors of the corporation as of May 29, 1986.


                                      /s/ Neil F. Baker
                                      ------------------------------------------
                                      Neil F. Baker, Secretary

                                     -14-