Within your herd there will be a large range of milking durations; some cows with very short milking durations to some with very long. The most common is about 6 minutes. If the rotation time was set at about 10 minutes, then, depending on the time of year, about 7% of the slowest milking cows would ‘go around’.
Speeding up the rotation time
Traditionally, farmers have aimed for less than 10% of cows 'going around'. If more than 10% required a second rotation, the platform speed would be reduced to give the cows longer to milk.
In fact, 'go around' cows do not negatively affect the number of cows milked per hour and aiming for less than 10% will often limit the platform throughput.
- Don’t worry about letting cows ‘go around’. Set the rotation time based on the ability of the ‘cups-on’ operator. It's better to keep cupping at a sensible rate throughout milking, rather than put undue effort or strain on the body trying to maintain an exhausting pace.
- Many rotary operators use the number of ‘going around’ cows as the criteria for setting rotation time but this can often limit efficiency.
How is speeding up more efficient?
The equation below shows which is more efficient.
Average cluster idle time for 10 min rotation; (3.6 minutes + 0.7 minutes) = 4.3 minutes.
Average cluster idle time for 8 min rotation; (1.8 minutes + 1.5 minutes) =3.3 minutes.
- Reducing cluster idle time or over-milking will improve milking efficiency. For the 10 minute rotation in this example, there is less cluster idle time using a shorter rotation time with more ‘go-around’ cows than a longer rotation time allowing less ‘go around’ cows.
- In a 50 bail rotary using this 10 minute rotation, each cluster would be idle for 3.6 minutes due to cows that have finished milking waiting to exit and 7% of bails would be used for ‘go around’ cows – an equivalent of an extra 0.7 minutes of idle cluster time.
- Shortening the rotation to 8 minutes would reduce cluster idle time to 1.8 minutes because for most cows they are finishing milking closer to the exit, but now 19% of bails would be occupied by a ‘go around’ cow so this idle time would increase to 1.5 minutes.
- Operators normally use the same rotation time regardless of rotary size. A bigger rotary will mean less operator time for each bail. As the speed increases, so does the percentage of ‘go around’ cows.
- When the rotary reaches the point where 20% of cows are ‘going around’ it is generally not more efficient to speed up the platform and shorten the rotation time (but it not less efficient either).
Points to think about when speeding up the platform
- Increasing the platform speed will mean the ‘cups on’ operator has less time to attach clusters. Ensure operators are using an efficient cupping technique.
- Increasing platform time will mean cows have less time to walk on and off the platform. Check your entry and exit area design to give yourself the best chance of good cow flow and fewer empty bails. The fastest cows can walk on in comfort is about 5 seconds/bail.
- If you don’t have automatic cluster removers, increasing the number of ‘go around’ cows will lessen the amount of cows being over-milked. But the cows that are over-milked will probably be over-milked longer so consider applying MaxT to prevent this and further improve efficiency.
- If you have an in-bail feeding system that will feed a ‘go around’ cow a second time, also look at applying MaxT to avoid this problem.