Rivals allegedly severed the wrist and fingers of two brothers as their cow ate bean trees at Baishakhola village in Kalapara upazila of the district on Saturday.
The victims are Humayun, 35, and his brother Saidul, 18, of the village. They are farmers by profession.
Police arrested the duo's neighbor Salma Begum, wife of Abdus Salam, in connection with the incident, said Md Monirul Islam, officer-in-charge of Kalapara Police Station.
Family members said Humayun's cow ate some bean trees of Salam. The latter then caught the cow and tied it with a tree.
When Humayun went to Salam's house to bring the cow in the evening, Salam and his men attacked Humyun with sharp weapons and cut off the wrist of his left hand and three fingers of right hand.
Hearing hue and cry, Saidul rushed to the spot and tried to save his brother. At that time, the attackers also cut off three fingers of Saidul's right hand.
The two brothers were rushed to the upazila health complex and then shifted to Barishal Sher-E-Bangla Medical College Hospital for better treatment.
A case was filed in this connection, said the OC.