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                                                                   Exhibit 4.5.1
                                                                   -------------

                   CERTIFICATE OF AMENDMENT TO CERTIFICATE OF
            DETERMINATION OF PREFERENCES OF SERIES B PREFERRED STOCK
                            OF SYNBIOTICS CORPORATION
                            a California corporation

     The undersigned, Paul A. Rosinack and Michael K. Green, hereby certify
that:

     A. Mr. Rosinack is the duly elected and acting President and Mr. Green is
the duly elected and acting Secretary of Synbiotics Corporation, a California
corporation (the "Corporation").

     B. Pursuant to the authority given by the Corporation's Articles of
Incorporation, as amended to date, the Board of Directors of the Corporation has
duly adopted the resolution attached as Exhibit A.
                                        ---------

     C. The authorized number of shares of Preferred Stock of the Corporation is
25,000,000, none of which has been issued. The authorized number of shares of
Series B Preferred Stock of the Corporation is 4,000, none of which has been
issued.

     IN WITNESS WHEREOF, the undersigned certify under penalty of perjury that
they have read the foregoing Certificate of Amendment to Certificate of
Determination and know the contents thereof, and that the statements therein are
true and correct of their own knowledge.

     Executed in San Diego, California on January 18, 2002.

                                                            /s/ Paul A. Rosinack
                                                            --------------------
                                                            Paul A. Rosinack
                                                            President

                                                            /s/ Michael K. Green
                                                            Michael K. Green
                                                            Secretary

<PAGE>

                                    Exhibit A
                                    ---------

     NOW, THEREFORE, BE IT RESOLVED, that Article 5, Section 5.1 of the
Certificate of Determination of Preferences of Series B Preferred Stock filed by
the Corporation with the Secretary of State of the State of California on
January 4, 2002 is hereby amended and restated to read as follows:

     "Section 5.1 Each share of Series B Preferred Stock shall be convertible,
at the option of the holder thereof, at any time after the Common Increase Date
(as defined below) and from time to time thereafter, into such number of fully
paid and nonassessable shares of Common Stock as is determined by dividing
$1,000.00 by the Conversion Price (as defined below) in effect at the time of
conversion. The Conversion Price at which shares of Common Stock shall be
deliverable upon conversion of Series B Preferred Stock without the payment of
additional consideration by the holder thereof (the "Conversion Price") shall
initially be $0.12846. Such initial Conversion Price, and the rate at which
shares of Series B Preferred Stock may be converted into shares of Common Stock,
shall be subject to adjustment as provided below.

     The "Common Increase Date" is the day the Corporation's Articles of
Incorporation are amended to increase the authorized number of shares of Common
Stock to at least 70,000,000. The Corporation covenants to use its best efforts
to cause the Common Increase Date to occur by no later than July 31, 2002.

     In the event of a liquidation of the Corporation, the Conversion Rights
shall terminate at the close of business on the first full day preceding the
date fixed for the payment of any amounts distributable on liquidation to the
holders of Series B Preferred Stock."<PAGE>

                                                                   Exhibit 10.79
                                                                   -------------

                            MANAGEMENT RETENTION PLAN

Synbiotics Corporation is implementing a "management retention plan" designed to
encourage you to remain an employee of the Company between now and the potential
sale of the Animal Health Business. The Management Retention Plan consists of a
cash or stock bonus and special treatment of outstanding stock options and
restricted stock. This Management Retention Plan does not alter or affect
existing Synbiotics employee benefit plans, the Special Payment Plan or existing
employee agreements.

To qualify for the Management Retention Plan, you must be an active employee,
who is employed on the day of the sale of the Animal Health Business, provided
that you have not notified the Company of your intent to resign your employment
with Synbiotics. This Management Retention Plan does not apply to:
                                                     ---

1)   Employees who voluntarily leave the Company prior to the sale of the Animal
     Health Business

2)   Employees whose employment is terminated prior to the sale of the Animal
     Health Business

3)   Employees of W3COMMERCE

4)   Active employees who are offered and accept continued employment with the
     Company following the sale of the Animal Health Business.

Cash Bonus

A cash bonus payment (or you can elect to receive the cash bonus in stock - see
below) will be made on the day following the sale of the Animal Health Business.
The bonus payment will depend on the ultimate sales price of the Animal Health
Business and will be paid as a percentage of annual base salary ("the
Percentage"). In no event will the Percentage payment be less than 25% of an
employee's annual base salary and there is no maximum percentage. The Percentage
will be calculated as 1.6666 times the sales price of the Animal Health
Business.

Examples:

     If the sales price of the Animal Health Business were $35 million, then 35
times 1.6666 would yield a Percentage of 58.88%. You would receive a cash bonus
of 58.33% of your annual salary.

<PAGE>

         If the sales price of the Animal Health Business were $60 million then
60 times 1.6666 would yield a Percentage of 100%. You would receive a cash bonus
of 100(degrees) of your annual salary.

Stock Bonus In-lieu of Cash Bonus

You may elect to receive all or a part of the aforementioned cash bonus in
stock. Such election must be made within 30 days of the execution date of this
agreement. If you choose to receive part of your cash bonus in stock, then the
number of shares to be received will be determined by dividing the cash bonus by
$3.

Example:

         If your cash bonus were $100,000 and you elected to receive $60,000 of
it in Stock, you would receive $40,000 in cash and 20,000 ($60,000/$3) shares of
Synbiotics stock.

Restricted Stock and Stock Options

All of your unvested restricted stock and stock options will become fully vested
on the day following the sale of the Animal Health Business and you will receive
two years following the sale of the Animal Health Business to exercise any
unexercised stock options.

/s/ Kenneth Cohen
----------------------
Kenneth Cohen
President and CEO
Synbiotics Corporation

I have read the above Management Retention Plan.
Acknowledged and accepted:

Paul A. Rosinack                  /s/ Paul A. Rosinack
----------------                  --------------------------
Print Name                        Employee Signature

June 16, 2000
-------------
Date<PAGE>

                                                                 Exhibit 10.79.1
                                                                 ---------------

                        AMENDED MANAGEMENT RETENTION PLAN

Synbiotics Corporation is implementing a "management retention plan" designed to
encourage you to remain am employee of the Company between now and the potential
sale of the Animal Health Business. The Management Retention Plan consists of a
cash or stock bonus and special treatment of outstanding stock options and
restricted stock. This Management Retention Plan does not alter or affect
existing Synbiotics employee benefit plans, the Special Payment Plan or existing
employee agreements.

To qualify for the Management Retention Plan, you must be an active employee,
who is employed on the day of the sale of the Animal Health Business, provided
that you have not notified the Company of your intent to resign your employment
with Synbiotics. This Management Retention Plan does not apply to:

1)   Employees who voluntarily leave the Company prior to the sale of the Animal
     Health Business

2)   Employees whose employment is terminated prior to the sale of the Animal
     Health Business

3)   Employees of W3COMMERCE

4)   Active employees who are offered and accept continued employment with the
     Company following the sale of the Animal Health Business.

Cash Bonus

A cash bonus payment (or you can elect to receive the cash bonus in stock - see
below) will be made on the day following the sale of the Animal Health Business.
The bonus payment will depend on the ultimate sales price of the Animal Health
Business and will be paid as a percentage of annual base salary ("the
Percentage"). In no event will the Percentage payment be less than 50% of an
employee's annual base salary and there is no maximum percentage. The Percentage
will be calculated as 1.666 times the sales price of the Animal Health Business.

Examples:

    If the sales price of the Animal Health Business were $35 million, then 35
times 1.666 would yield a Percentage of 58.33%. You would receive a cash bonus
of 58.33% of your annual salary.

<PAGE>

         If the sales price of the Animal Health Business were $60 million then
60 times 1.666 would yield a Percentage of 100%. You would receive a cash bonus
of 100% of your annual salary.

Restricted Stock and Stock Options

All of your unvested restricted stock and stock options will become fully vested
on the day following the sale of the Animal Health Business and you will receive
two years following the sale of the Animal Health Business to exercise any
unexercised stock options.

/s/ Kenneth M. Cohen
---------------------------------
Kenneth M. Cohen
President and CEO
Synbiotics Corporation

I have read the above Management Retention Plan.
Acknowledged and accepted:

/s/ Paul A. Rosinack
----------------------
Paul A. Rosinack

January 24, 2001
----------------
Date

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