The version I found had one additional verse:

My house now lacks the glamour that the charming creature gave,
The garage where I kept him is as silent as the grave;
No longer he displays among the motor-tires and spanners
His hippopotamastery of hippopotamanners.

No longer now he gambols in the orchard in the Spring;
No longer do I lead him through the village on a string;
No longer in the mornings does the neighborhood rejoice
To his hippopotamusically-modulated voice.

I had a hippopotamus; but nothing upon earth
Is constant in its happiness or lasting in its mirth.
No joy that life can give me can be strong enough to smother
My sorrow for that might-have-been-a-hippopotamother.

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I found it on this page: http://members.aol.com/HippoPage/hipppoem.htm