Is it this one?:
A Poem on How To Tell The Age of Horses:
To tell the age of any horse,
inspect the lower jaw, of course;
The six front teeth the tale will tell,
and every fear and doubt dispel.
Two middle "nippers" you behold
Before the colt is two weeks old;
Before eight weeks two more will come;
eight months, "the corners" cut the gum.
The outside grooves will disappear.
From middle two in just one year;
In two years the second pair;
in three the "corners," too, are bare.
At two the middle "nippers" drop;
at three the second pair can't stop;
When four year old the third pair goes;
at five a full new set he shows.
The deep black spots will pass from view,
at six years from the middle two;
The second pair at seven years;
At eight the spot each "corner" clears.
From middle "nippers," upper jaw,
at nine the black spots will withdraw;
The second pair at ten are white;
Eleven finds the "corners" light.
As time goes on the horsemen know
the oval teeth three-sided grow;
They longer get, project before,
Till twenty, when we know no more.
