Sentence:  The barbarous custom of docking and <WSD>nicking</WSD> the tail, and cutting the ears of horses, is too prevalent. [...] [I]n the loss of their tail, they find even a still greater inconvenience. During summer they are perpetually teazed with swarms of insects that either attempt to suck their blood or deposit their eggs in the rectum, which they have no means of lashing off; and in winter they are deprived of a necessary defence against the cold. [From the "Boston Yankee".] 
Meaning of the word marked with <WSD> tags:  To make a crosscut or cuts on the underside of (the tail of a horse, in order to make the animal carry it higher).