The reason Dennis Hanks gives for this removal was a disease called the "milk-sick.".    From Wordnik.com.  [McClure's Magazine December, 1895] Reference

Sparrow were both seized with a terrible disease known to the settlers as the "milk-sick" because it attacked the cattle.    From Wordnik.com.  [The Story of Young Abraham Lincoln] Reference

For a week the milk-sick fever had raged furiously, and in the few hours free from delirium she had been racked with omnipresent pain and deadly sickness.    From Wordnik.com.  [The Path of the King] Reference

In the autumn of 1818 the little community of Pigeon Creek was almost exterminated by a frightful pestilence called the milk-sickness, or, in the dialect of the country, "the milk-sick.".    From Wordnik.com.  [Abraham Lincoln: a History — Volume 01] Reference

Fourth, if it had been a vegetable which prduced the milk-sick, it would have been found long ago; for, to my own knowledge it has been diligently searched for in many places, by numerous people and not found.    From Wordnik.com.  [The Cherokee Physician, or Indian Guide to Health, as Given by Richard Foreman, a Cherokee Doctor; Comprising a Brief View of Anatomy, With General Rules for Preserving Health without the Use of Medicines. The Diseases of the U. States, with Their Symptoms, Causes, and Means of Prevention, are Treated on in a Satisfactory Manner. It Also Contains a Description of a Variety of Herbs and Roots, Many of which are not Explained in Any Other Book, and their Medical Virtues have Hitherto been Unknown to the Whites; To which is Added a Short Dispensatory.] Reference

'milk-sick' because the cows die, too -- and sometimes the horses.    From Wordnik.com.  [The Southerner A Romance of the Real Lincoln] Reference

It was called the “milk-sick.”.    From Wordnik.com.  [The Life of Abraham Lincoln]

It was called the "milk-sick.".    From Wordnik.com.  [The Life of Abraham Lincoln] Reference