A dispenser for dispensing fluid that, integrated into one hand piece , comprises: a variable volume chamber with a plunger disposed within the chamber and a chamber inlet and outlet , the inlet and outlet communicating directly with a common chamber volume , wherein the plunger translates in a linear direction relative to the chamber along a common longitudinal axis; at least one controller that is operatively linked to the plunger and chamber ; a power source and a motor that drives translation movement of the plunger thereby causing a change in volume in the chamber ; a trigger ; at least one sensor for measuring a varied second or intermediate position of the plunger ; and characterised in that , the dispenser is configured such that when the trigger is actuated the plunger translates to expel fluid in the chamber during an expel stroke and thereafter, draw fluid into the chamber during a drawing stroke with the at least one controller wirelessly receiving a measured weight input based on the weight of an animal to which the fluid is to be applied and, controlling the volume expelled from the chamber corresponding to the animal weight by adjusting the plunger position along the longitudinal axis during an expel stroke from an initial position to a varied second sensor measured position or intermediate position thereby varying the volume of fluid expelled from the chamber and thereby automatically varying the volume of fluid expelled from the chamber for each animal to which fluid is applied. a variable volume chamber with a plunger disposed within the chamber and a chamber inlet and outlet , the inlet and outlet communicating directly with a common chamber volume , wherein the plunger translates in a linear direction relative to the chamber along a common longitudinal axis; at least one controller that is operatively linked to the plunger and chamber ; a power source and a motor that drives translation movement of the plunger thereby causing a change in volume in the chamber ; a trigger ; at least one sensor for measuring a varied second or intermediate position of the plunger ; and characterised in that , the dispenser is configured such that when the trigger is actuated the plunger translates to expel fluid in the chamber during an expel stroke and thereafter, draw fluid into the chamber during a drawing stroke with the at least one controller wirelessly receiving a measured weight input based on the weight of an animal to which the fluid is to be applied and, controlling the volume expelled from the chamber corresponding to the animal weight by adjusting the plunger position along the longitudinal axis during an expel stroke from an initial position to a varied second sensor measured position or intermediate position thereby varying the volume of fluid expelled from the chamber and thereby automatically varying the volume of fluid expelled from the chamber for each animal to which fluid is applied. when the trigger is actuated the plunger translates to expel fluid in the chamber during an expel stroke and thereafter, draw fluid into the chamber during a drawing stroke with the at least one controller wirelessly receiving a measured weight input based on the weight of an animal to which the fluid is to be applied and, controlling the volume expelled from the chamber corresponding to the animal weight by adjusting the plunger position along the longitudinal axis during an expel stroke from an initial position to a varied second sensor measured position or intermediate position thereby varying the volume of fluid expelled from the chamber and thereby automatically varying the volume of fluid expelled from the chamber for each animal to which fluid is applied. <EOS>