<PAGE>   1

                                                                     EXHIBIT 9.5


                        FOURTH AMENDMENT TO FIRST AMENDED
                        AND RESTATED INVESTORS' AGREEMENT

         This Fourth Amendment to the First Amended and Restated Investors'
Agreement (this "AGREEMENT") dated as of May 4, 1999, is entered into by and
among (i) Doane Pet Care Enterprises, Inc., formerly known as DPC Acquisition
Corp. (the "COMPANY"), (ii) Doane Pet Care Company formerly known as Doane
Products Company ("Doane"), (iii) Summit Capital Inc. ("SUMMIT"), (iv)
Summit/DPC Partners, L.P. ("SUMMIT/DPC"), (v) Chase Manhattan Investment
Holdings, Inc. ("CHASE"), (vi) DLJ Merchant Banking Partners, L.P., DLJ
International Partners, C.V., DLJ Offshore Partners, C.V., DLJ Merchant Banking
Funding, Inc., DLJ First ESC, L.L.C., (each of the foregoing in this clause
(vi), a "DLJ ENTITY," and collectively, the "DLJ ENTITIES"), (vii) Dartford
Partnership, L.L.C. ("DARTFORD"), (viii) Bruckmann, Rosser, Sherrill & Co., L.P.
("BRS"), (ix) PNC Capital Corp ("PNC"), (x) Windy Hill Pet Food Company, L.L.C.
("WINDY HILL L.L.C."), (xi) Baseball Partners and (xii) the other Persons listed
on the signature pages hereto.

                              W I T N E S S E T H :

         WHEREAS, certain stockholders and warrantholders of the Company are
parties to or bound by that certain First Amended and Restated Investors'
Agreement dated as of August 3, 1998, as amended to date (the "ORIGINAL
AGREEMENT"); and

         WHEREAS, the undersigned, constituting the holders of more than 75% of
the shares of Common Stock of the Company (including the Warrants on an "as-if
exercised" basis) desire to amend the Original Agreement on the terms of this
Agreement and, except as amended by this Agreement, ratify the terms of the
Original Agreement.

         NOW, THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, and in exchange for the mutual
covenants herein, the parties hereto agree as follows:

                                   AGREEMENTS

1. Defined Terms. Capitalized terms used in this Agreement that are not defined
herein shall have the meanings given to them in the Original Agreement.

2. Amendments. The Original Agreement is hereby amended as follows:

         (a) Section 1.1(a) is amended by adding the following defined terms:

                  "BYLAWS" means the bylaws of the Company, as amended or
         restated from time to time.

                  "CLASS I DIRECTOR" means any director of the Board then
         serving in one of the Board positions specified as a "Class I" position
         by the Bylaws of Company.



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                  "CLASS II DIRECTOR" means any director of the Board then
         serving in one of the Board positions specified as a "Class II"
         position by the Bylaws of Company.

                  "CLASS III DIRECTOR" means any director of the Board then
         serving in one of the Board positions specified as a "Class III"
         position by the Bylaws of Company.

(b)      Section 2.1(a) is hereby amended in its entirety to provide as follows:

         "(a) The Board shall consist of eight members or such greater number as
         is established in accordance with the Bylaws, and the Company shall
         take such action as is necessary to cause the following persons to be
         nominated, in accordance with the Bylaws, to stand for election to
         serve as directors in the positions (i.e., as Class I Directors, Class
         II Directors or Class III Directors) specified below:

                  (i) (A) at any time the Summit-Investors own of record 50% or
                  more of the number of shares of Common Stock owned thereby as
                  of August 3, 1998 (in each case, disregarding stock splits,
                  recapitalizations and similar adjustments in number of shares
                  and stock dividends), two individuals designated by Summit on
                  behalf of the Summit-Investors, and, as long as the Board is
                  classified, of such two individuals, one shall stand for
                  election as a Class III Director and the second individual
                  shall stand for election as a Class II Director (each such
                  person, a "SUMMIT-INVESTOR DESIGNEE") and (B) at any time the
                  Summit-Investors own of record less than 50% of the number of
                  shares of Common Stock owned thereby as of August 3, 1998
                  (disregarding stock splits, recapitalizations, and similar
                  adjustments in number of shares and stock dividends) and the
                  Summit-Investors' Percentage Ownership is 5% or more, one
                  individual designated by Summit on behalf of the
                  Summit-Investors and, so long as the Board is classified, such
                  individual shall stand for election as a Class III Director;

                  (ii) (A) at any time the Windy Hill Investors own of record
                  (or beneficially by reason of the record ownership of IBJ
                  Whitehall Bank & Trust Company (formerly IBJ Schroder Bank &
                  Trust Company) ("IBJ")) 50% or more of the number of shares of
                  Common Stock owned thereby as of August 3, 1998 (in each case,
                  disregarding stock splits, recapitalizations and similar
                  adjustments in number of shares and stock dividends), one
                  individual designated by Windy Hill L.L.C., which individual
                  shall stand for election as a Class II Director, and one
                  individual designated by BRS, which individual shall stand for
                  election as a Class I Director (such two designees
                  collectively referred to as the "WINDY HILL DESIGNEES" or
                  individually as a "WINDY HILL DESIGNEE") and (B) at any time
                  the Windy Hill Investors own of record (or beneficially by
                  reason of the record ownership of IBJ less than 50% of the
                  number of shares of Common Stock owned thereby as of August 3,
                  1998 (in each case, disregarding stock



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                  splits, recapitalizations and similar adjustments in number of
                  shares and stock dividends) and the Windy Hill Investors'
                  Percentage Ownership is 5% or more, the Windy Hill
                  Representative shall be nominated to stand for election and,
                  so long as the Board is classified, the Windy Hill
                  Representative shall stand for election to serve as a Class II
                  Director;

                  (iii) at any time the Chase Percentage Ownership is 5% or
                  greater, one individual shall be designated by Chase (the
                  "CHASE DESIGNEE") to stand for election and, so long as the
                  Board is classified, the Chase Designee shall stand for
                  election to serve as a Class III Director;

                  (iv) at any time the DLJMB's Percentage Ownership is 5% or
                  greater, one individual shall be designated by DLJMB (the
                  "DLJMB DESIGNEE") to stand for election and, so long as the
                  Board is classified, the DLJMB Designee shall stand for
                  election to serve as a Class III Director;

                  (v) the chief executive officer of the Company shall be
                  designated to stand for election and, so long as the Board is
                  classified, the chief executive officer shall stand for
                  election to serve as a Class II Director; and

                  (vi) in addition to the individuals contemplated above, one
                  individual designated jointly by George B. Kelly (so long as
                  Mr. Kelly serves as a member of the Board and the Summit
                  Investors' Percentage Ownership is 5% or more) and by the
                  DLJMB Designee (so long as DLJMB's Percentage Ownership is 5%
                  or more); provided, if either Mr. Kelly or the DLJMB Designee
                  is not entitled to designate the individual pursuant to this
                  clause (vi) because the conditions set forth in either of the
                  foregoing parentheticals have not been satisfied, the
                  individual shall be designated pursuant to this clause (vi) by
                  Mr. Kelly (if the Summit Investors' Percentage Ownership is 5%
                  or greater) or by DLJMB Designee (if the DLJBM's Percentage
                  Ownership is 5% or greater) (such individual being referred to
                  as the "JOINT DESIGNEE" even if such individual is designated
                  by either Mr. Kelly or the DLJMB Designee pursuant to the
                  foregoing proviso).

                  Director positions for which a nominee is not specified in
         accordance with the preceding provisions of this Section 2.2(a) shall
         be specified in accordance with the Bylaws.

                  At the Company's request, each Shareholder entitled to vote
         for the election of directors to the Board shall vote its Securities
         and execute written consents to increase the Board size and to elect
         independent directors to accommodate the requirements for listing the
         Securities on any national securities exchange or market system on
         which the Board determines that the Securities shall be listed or
         included or to include at least two individuals who are "NON-EMPLOYEE
         DIRECTORS" for purposes of, and as such term is referred to in, Rule
         16b-3



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         of the Exchange Act. Each Shareholder entitled to vote for the election
         of directors to the Board agrees that it will vote its Securities or
         execute consents, as the case may be, and take all other reasonable
         action (including taking reasonable steps to cause the Company to call
         a special meeting of shareholders) in order to ensure that the
         composition of the Board is as set forth in this Section 2.1(a). The
         parties to this Agreement acknowledge and agree that, due to the
         existence of stockholders entitled to vote for the election of
         directors that are not parties to this Agreement, the right to
         designate an individual pursuant to this Section 2.1(a) and the
         obligations of the Shareholders to vote for or consent to any
         individual designated in accordance with this Section 2.1(a) may not be
         sufficient to ensure that such individual shall be elected to the
         Board."

(c)      Section 2.2 is hereby amended in its entirety to provide as follows:

         "Removal and Resignation.

                  (a) Each Shareholder agrees that it will not vote any of its
                  Securities in favor of the removal of any director who shall
                  have been designated or nominated pursuant to Section 2.1(a)
                  unless (i) such removal shall be for Cause (as defined below)
                  or (ii) the Person(s) entitled to designate or nominate such
                  director shall have consented to or requested such removal in
                  writing (and, in the case of any such request, such
                  Shareholder shall vote its Securities in favor of such
                  removal). Removal for "Cause" shall mean removal of a director
                  because of such director's (A) willful and continued failure
                  substantially to perform his duties with the Company in his
                  established position, (B) willful conduct which is injurious
                  to the Company or any of its Subsidiaries, monetarily or
                  otherwise, (C) conviction for, or guilty plea to, a felony or
                  a crime involving moral turpitude, (D) abuse of illegal drugs
                  or other controlled substances or habitual intoxication or (E)
                  willful breach of this Agreement.

                  (b) (i) At any time there are two Summit-Investor Designees
                  serving on the Board when (A) the Summit-Investors own of
                  record less than 50% of the number of shares of Common Stock
                  owned thereby as of August 3, 1999 (disregarding stock splits,
                  recapitalizations and similar adjustments in the number of
                  shares and stock dividends) and (B) the Summit-Investors'
                  Percentage Ownership is 5% or greater, upon the request of a
                  majority of the other directors, the Summit-Investors shall
                  use their commercial best efforts to cause one of the two
                  Summit-Investor Designees to resign, and the resigning
                  Summit-Investor Designee shall be the individual identified by
                  George B. Kelly or, if Mr. Kelly fails to identify the
                  resigning Summit-Investor Designee, the resigning
                  Summit-Investor Designee shall be the Summit-Investor Designee
                  that is not Mr. Kelly or (ii) at any time there are any
                  Summit-Investor Designees serving on the Board when the
                  Summit-Investors' Percentage Ownership is less than 5%, upon
                  the request of a majority of the other directors of the Board,



                                      -4-
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                  the Summit-Investors shall use their commercial best efforts
                  to cause each Summit-Investor Designee to resign from the
                  Board;

                  (c) (i) At any time there are two Windy Hill Designees serving
                  on the Board when (A) the Windy Hill Investors own of record
                  (or beneficially by reason of the record ownership of IBJ)
                  less than 50% of the number of shares of Common Stock owned
                  thereby as of August 3, 1999 (disregarding stock splits,
                  recapitalizations and similar adjustments in the number of
                  shares and stock dividends) and (B) the Windy Hill Investors'
                  Percentage Ownership is 5% or greater, upon the request of a
                  majority of the other directors, the Windy Hill Investors
                  shall use their commercial best efforts to cause one of the
                  two Windy Hill Investor Designees to resign, and the resigning
                  Windy Hill Designee shall be the individual identified by the
                  Windy Hill Representative or, if the Windy Hill Representative
                  fails to identify the resigning Windy Hill Designee, the
                  resigning Windy Hill Designee shall be the Windy Hill Designee
                  that is not the Windy Hill Representative or (ii) at any time
                  there are any Windy Hill Designees serving on the Board when
                  the Windy Hill Investors' Percentage Ownership is less than
                  5%, upon the request of a majority of the other directors of
                  the Board, the Windy Hill Investors shall use their commercial
                  best efforts to cause each Windy Hill Designee to resign from
                  the Board;

                  (d) at any time the Chase Designee is serving on the Board
                  when Chase's Percentage Ownership is less than 5%, upon the
                  request of a majority of the other directors of the Board,
                  Chase shall use its commercial best efforts to cause the Chase
                  Designee to resign from the Board;

                  (e) at any time the DLJMB Designee is serving on the Board
                  when DLJMB's Percentage Ownership is less than 5%, upon the
                  request of a majority of the other directors of the Board,
                  DLJMB shall use its commercial best efforts to cause the DLJMB
                  Designee to resign from the Board; and

                  (f) at any time the Joint Designee is serving on the Board
                  when both the Summit Investors' Percentage Ownership is less
                  than 5% and the DLJMB's Percentage Ownership is less than 5%,
                  upon the request of the majority other directors of the Board,
                  Summit and DLJMB shall use their respective commercial best
                  efforts to cause the Joint Designee to resign from the Board.

(d)      Section 2.3 is hereby amended in its entirety to provide as follows:

         "2.3 Vacancies . The Shareholders recognize that under the terms of the
         certificate of incorporation and the bylaws that any vacancy in the
         Board, whether arising through death, resignation, or removal of a
         director, or through an increase



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         in the number of directors of any class, shall be filled by the
         majority vote of the remaining directors, although less than a quorum,
         or by a sole remaining director. In the event of such vacancy, each
         Shareholder entitled to vote for the election of directors to the Board
         agrees that it will use commercial best efforts to cause its Board
         nominee, if any and if then serving on the Board, to fill any such
         vacancy in the following manner:

                  (a) any vacancy created by the death, disability, retirement,
                  resignation or removal of any individual (a "FORMER DIRECTOR")
                  designated under clauses (i), (ii), (iii) or (v) of Section
                  2.1(a) shall be filled by the applicable person or persons
                  that designated the Former Director so long such person or
                  persons remains entitled to designate an individual under the
                  applicable clause of Section 2.1(a); and

                  (b) any vacancy created by an increase in the number of
                  directors of any class shall be filled in accordance with the
                  Bylaws."

(e)      Section 4.1(a) is amended by replacing the word "Person" for the words
         "Third Party" in the first (and only) sentence of Section 4.1(a).

3. Terminology. The phrases "AS OF THE DATE OF THIS AGREEMENT" and "THE DATE
HEREOF," when used in the text of the Original Agreement, refer to August 3,
1998.

4. Ratification. Except as expressly set forth herein, the terms and provisions
of the Original Agreement, as amended prior to the date hereof, are hereby
ratified and confirmed.

5. Miscellaneous. This Agreement may be executed in one or more counterparts,
each of which shall be deemed to be an original, but all of which shall
constitute one and the same agreement.

         IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
duly executed by their respective authorized officers as of the day and year
first above written.

                                        DOANE PET CARE ENTERPRISES, INC.

                                        By:  /s/ THOMAS R. HEIDENTHAL
                                           -------------------------------------
                                             Thomas R. Heidenthal
                                             Senior Vice President & CFO


                                        DOANE PET CARE COMPANY

                                        By:  /s/ THOMAS R. HEIDENTHAL
                                           -------------------------------------
                                             Thomas R. Heidenthal
                                             Senior Vice President & CFO



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                                        SUMMIT CAPITAL INC.

                                           By: /s/ GEORGE B. KELLY
                                              ----------------------------------
                                                George B. Kelly
                                                Chairman


                                        CHASE MANHATTAN INVESTMENT
                                           HOLDINGS, INC.

                                           By: /s/ JEFFREY C. WALKER
                                              ----------------------------------
                                           Name:   Jeffrey C. Walker
                                                --------------------------------
                                           Title:  CEO
                                                 -------------------------------

                                        BASEBALL PARTNERS

                                           By: /s/ CHRIS BEHRENS
                                              ----------------------------------
                                           Name:   Chris Behrens
                                                --------------------------------
                                           Title:  General Partner
                                                 -------------------------------

                                        SUMMIT/DPC PARTNERS, L.P.

                                           BY: SUMMIT CAPITAL, INC.,
                                                 its General Partner

                                           By: /s/ GEORGE B. KELLY
                                              ----------------------------------
                                                George B. Kelly
                                                Chairman


                                        DLJ MERCHANT BANKING PARTNERS, L.P.,
                                           a Delaware Limited Partnership

                                           BY: DLJ MERCHANT BANKING, INC.
                                               Managing General Partner

                                           By: /s/ PETER GRAUER
                                              ----------------------------------
                                           Name:   Peter Grauer
                                                --------------------------------
                                           Title:  Managing Director
                                                 -------------------------------

                                        DLJ INTERNATIONAL PARTNERS, C.V.

                                           BY: DLJ MERCHANT BANKING, INC.
                                                  Advisory General Partner

                                           By: /s/ PETER GRAUER
                                              ----------------------------------
                                           Name:   Peter Grauer
                                                --------------------------------
                                           Title:  Managing Director
                                                 -------------------------------



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<PAGE>   8


                                        DLJ OFFSHORE PARTNERS, C.V.

                                           BY: DLJ MERCHANT BANKING, INC.
                                                  Advisory General Partner

                                           By: /s/ PETER GRAUER
                                              ----------------------------------
                                           Name:   Peter Grauer
                                                --------------------------------
                                           Title:  Managing Director
                                                 -------------------------------

                                        DLJ FIRST ESC, L.L.C.

                                           By: /s/ PETER GRAUER
                                              ----------------------------------
                                           Name:   Peter Grauer
                                                --------------------------------
                                           Title:  Managing Director
                                                 -------------------------------


                                        DLJ MERCHANT BANKING FUNDING, INC.

                                           By: /s/ PETER GRAUER
                                              ----------------------------------
                                           Name:   Peter Grauer
                                                --------------------------------
                                           Title:  Managing Director
                                                 -------------------------------

                                        THE ROSENTHAL 1989 TRUST

                                           By:
                                              ----------------------------------
                                           Name:
                                                --------------------------------
                                           Title:
                                                 -------------------------------


                                        By:
                                           -------------------------------------
                                                     Dick H. Weber

                                        By:
                                           -------------------------------------
                                                     Terry W. Bechtel

                                        By:      /s/ BOB L. ROBINSON
                                           -------------------------------------
                                                     Bob L. Robinson

                                        ROBINSON MANAGEMENT L.P.

                                           By:   /s/ BOB L. ROBINSON
                                              ----------------------------------
                                           Name:     Bob L. Robinson
                                                --------------------------------
                                           Title:    Managing Partner
                                                 -------------------------------



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<PAGE>   9


                                        BOB L. ROBINSON GRANTOR RETAINED
                                        ANNUITY TRUST

                                           By: /s/ BOB L. ROBINSON
                                              ----------------------------------
                                           Name:   Bob L. Robinson
                                                --------------------------------
                                           Title:  Trustee
                                                 -------------------------------

                                        JEANINE L. ROBINSON GRANTOR RETAINED
                                        ANNUITY TRUST

                                           By: /s/ JEANINE L. ROBINSON
                                              ----------------------------------
                                           Name:   Jeanine L. Robinson
                                                --------------------------------
                                           Title:  Trustee
                                                 -------------------------------


                                        By:
                                           -------------------------------------
                                                    Roy E. Hess


                                        By:
                                           -------------------------------------
                                                    Earl R. Clements


                                        By:
                                           -------------------------------------
                                                    J. David Heaney


                                        By:     /s/ LAURA HAWKINS MANSUR
                                           -------------------------------------
                                                    Laura Hawkins Mansur


                                        By:     /s/ WALID MANSUR
                                           -------------------------------------
                                                    Walid Mansur

                                        THE KAREEM ROBERT MANSUR TRUST

                                        By:     /s/ WALID MANSUR, TRUSTEE
                                           -------------------------------------
                                                    Walid Mansur, Trustee



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<PAGE>   10


                                        THE SARA SELMA MANSUR TRUST

                                        By:   /s/ WALID MANSUR
                                           -------------------------------------
                                                  Walid Mansur, Trustee

                                        THE LEILA MARIAM MANSUR TRUST

                                        By:   /s/ WALID MANSUR
                                           -------------------------------------
                                                  Walid Mansur, Trustee


                                        By:
                                           -------------------------------------
                                                    Gary L. Rosenthal


                                        By:
                                           -------------------------------------
                                                    Lee H. Rosenthal


                                        By:
                                           -------------------------------------
                                                    Ferd A. Rosenthal



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<PAGE>   11


         The following signatories are the "WINDY HILL INVESTORS." Each of the
Windy Hill Investors and IBJ Whitehall Bank & Trust Company ("IBJ") are parties
to an escrow and pledge agreement dated August 3, 1998 pursuant to which IBJ, as
escrow and collateral agent, is the record holder of all shares of Common Stock
beneficially owned by the Windy Hill Investors. Each of the undersigned Windy
Hill Investors, as evidenced by its signature below, hereby directs IBJ to enter
into this Agreement.


                                        DARTFORD PARTNERSHIP, L.L.C.

                                           By:  /s/ RAY CHUNG
                                              ----------------------------------
                                           Name:    Ray Chung
                                                --------------------------------
                                           Title:   Executive Vice President
                                                 -------------------------------


                                           BRUCKMANN, ROSSER, SHERRILL &
                                           CO., L.P.

                                           By:   /s/ STEPHEN SHERRILL
                                              ----------------------------------
                                           Name:     Stephen Sherrill
                                                --------------------------------
                                           Title:    Managing Director
                                                 -------------------------------


                                        PNC CAPITAL CORP

                                           By:
                                              ----------------------------------
                                           Name:
                                                --------------------------------
                                           Title:
                                                 -------------------------------


                                        WINDY HILL PET FOOD COMPANY L.L.C.

                                           By:  /s/ RAY CHUNG
                                              ----------------------------------
                                           Name:    Ray Chung
                                                --------------------------------
                                           Title:   Executive Vice President
                                                 -------------------------------

                                                /s/ ROBERT V. DALE
                                           -------------------------------------
                                                    Robert V. Dale

                                                /s/ F. DONALD COWAN, JR.
                                           -------------------------------------
                                                    F. Donald Cowan, Jr.



                                      -11-
<PAGE>   12


                                           -------------------------------------
                                                    Donald L. Gadd


                                           -------------------------------------
                                                    Henry G. Hurd, Jr.


                                           -------------------------------------
                                                    Ben W. McCrory


                                           -------------------------------------
                                                    Vaughn R. Oakley


                                           -------------------------------------
                                                    Charles Dunleavy


                                        BCB PARTNERSHIP, BRUCE C. BRUCKMANN,
                                        DONALD J. BRUCKMANN, PAUL D. KAMINSKI,
                                        NAZ PARTNERSHIP, HAROLD O. ROSSER, H.
                                        VIRGIL SHERRILL, STEPHEN C. SHERRILL,
                                        NANCY A. ZWENG, ELIZABETH MCSHANE,
                                        BEVERLY PLACE, BY THE FOLLOWING PERSONS:

                                        By: /s/ STEPHEN C. SHERRILL
                                           -------------------------------------
                                           Stephen C. Sherrill, Attorney-in-Fact

                                            /s/ STEPHEN C. SHERRILL
                                           -------------------------------------
                                           Stephen C. Sherrill, Individually




                                      -12-
<PAGE>   13


                                        IBJ WHITEHALL BANK & TRUST COMPANY, as
                                        escrow and collateral agent and record
                                        holder for the shares of Common Stock
                                        beneficially owned by the Windy Hill
                                        Investors set forth above.


                                        By:  /s/ BARBARA McCLUSKY
                                           -------------------------------------
                                        Name:    Barbara McClusky
                                             -----------------------------------
                                        Title:   Vice President
                                              ----------------------------------




                                      -13-