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Robots, Milk Speed and Your Bottomline

An important KPI to consider for an AMS herd is the time needed to milk the cows. This is a combination of the time needed to prepare the cow before milking (stimulation time or treatment time), the milking time, and the post milking time. The combination of these steps determines the box time.

A typical box time is around 6:30 to 7:00 min. An important component of the time the cows spend milking is the milk speed. Milk Speed refers to the kg of milk/minute of milking time or minute of box time. This is a very important factor in robotic milking since cows with faster milk speeds can produce the same milk in less time, hence freeing the robot for another cow to be milked sooner. This becomes especially important as the robot reaches capacity, for example when adding more cows due to extra quota or incentive days. 

Milk speed is determined primarily by genetics and udder preparation at beginning of milking. Because milk speed is a genetic trait, cows can be selected for this trait, so in time it is better to have a barn with cows that milk faster than with cows that milk slower. A normal benchmark for milk speed is to have cows milking more than 2.33 kg/min of milking time or 1.9 kg/min of box time. These benchmarks provide some indication about the suitability of a cow for robot milking. Cows that are very slow milking may take a disproportionate amount of robot time for the amount of milk they produce.

In situations where we are trying to maximize robot output (milk ≥ 2400kg milk/robot/day or milk fat ≥ 90 kg/day), slow milking cows are a serious impediment to achieving these goals. However, excessively high milk speed (>3 kg milk/minute) is also undesirable as it is associated with an increased risk of intra-mammary infection or mastitis. This suggests that we need to strike a balance between selecting for higher milk speed and the need to keep the prevalence of mastitis low in the herd. It may be better to remove slow milking cows, particularly if they are also low producers. This will increase the average milk speed in the herd, which becomes more important the closer the robot is to capacity.

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Box time can provide an evaluation of other aspects as well. For example if this KPI is high, say above 7:30 min, it may indicate that the udders or tails are dirty or need singeing, increasing cleaning/treatment time. It also may be a consequence of poor teat/udder conformation or that the camera needs cleaning.

As with any other KPI, the numbers should be evaluated carefully. For example, a cow with a box time of 9:00 minutes might seem excessive but if for example that cow milks 2.2 kg/min of box time and has 2.7 turns/day, she’ll end up producing 53.5 kg of milk at the end of the day, so is probably worth keeping. 

Depending on the goals of the farm (kg fat/robot/day), the “slowest” milking cows should be culled over time and the heifers from these cows are not likely to make better “robot cows”. Cow temperament and behavior is very important when selecting cows as well. Cows that are nervous or stressed and start kicking the robot, will increase the time needed to be milked and consequently, kg per robot will decrease.

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