The cost of a milking center can represent one-half the total cost of dairy cattle housing. Thus, you want to pay close attention to every detail that goes into the milking center, including the size of the parlor you plan to install.

Parallel, herringbone and rotary parlors are the three most common types of parlors. After you’ve decided which type of parlor you’d like to install, size it to meet your dairy’s needs.

Use the steps listed under “Parallel and herringbone parlors” or “Rotary parlors” to help you do so.

- Parallel and herringbone parlors

Use these steps to help you determine the number of stalls to put in your parallel or herringbone parlor:

Step 1. Determine milking frequency

Before you sit down with an equipment company to discuss the size of your parlor, you need to establish some parameters. As a starting point, consider how many times per day you want to milk cows.

Milking frequency, or the number of milkings per day, will dictate the number of turns in a parlor, says Dennis Armstrong, a retired professor and parlor efficiency expert from the University of Arizona.

Suppose, for example, you choose to milk three times per day, and each shift averages 6.5 hours long, for a total milking time of 19.5 hours per day. In order to turn the parlor five times per hour, you must allow 30 seconds to one minute for cows to enter and exit the parlor, three to 3.5 minutes for pre-milking udder hygiene and unit attachment and eight minutes for milking time, for a total of 12 minutes per group. Remember, these parameters are only guidelines to help you estimate milking frequency, shift length and turns per hour. Parlor efficiency will depend on many factors. Discuss them with your equipment company representative before sizing the parlor. That way, you can meet your particular goals for parlor efficiency. (Please see “Many factors influence parlor efficiency” below).

Because of smaller herd size, some dairies may consider milking a set number of hours per day, such as four to six hours per day, says John Smith, extension dairy specialist at Kansas State University. For example, on a 200-cow dairy, a parlor could be sized to milk 100 cows per hour.

Step 2. Consider labor needs

During the planning process, start thinking about the pre-milking hygiene routine you plan to follow and the number of operators you need to run your parlor efficiently. The number of operators is determined by many factors, including your pre-milking hygiene routine.

Step 3. Calculate the number of stalls

While it’s imperative to consider milking frequency and labor needs, it’s equally important to consider the number of cows you plan to milk now and in the future, as well as potential milk production. Ask yourself, “How many cows am I going to milk five, seven or 15 years from now?”

Then, using the milking frequency table shown above, plug some numbers into the following simple calculation to estimate the number of stalls you’ll need:

Total number of cows

÷ hours per shift

= cows milked per hour

Cows milked per hour

÷ number of turns per hour

= number of stalls needed

For example:

1,200 total cows

÷ 6.5 hours per shift when milking 3x

= 184 cows milked per hour

184 cows

÷ 5 turns per hour

= 36 stalls, or a double-18 parlor

Thus, you need to install a double-18 parallel or herringbone parlor — at a minimum — to milk 1,200 cows in a 6.5-hour time period. However, Armstrong suggests over-sizing the parlor a little for future increases in milk production, so he would prefer installing a double-20 parlor in this instance.

- Rotary parlors

Use these steps to help you determine the number of stalls to put in a rotary parlor:

Step 1. Establish rotation time

Rotation time, or entry time, influences the number of stalls you’ll need in a rotary parlor. Rotation time is measured in seconds per stall. Parlor efficiency experts recommend an entry time of seven to 12 seconds per stall to maximize cow throughput.

Step 2. Consider cow throughput

Rotation time determines the total number of cows that you can milk per hour. For example, if a cow enters the platform every 10 seconds, the maximum throughput or “theoretical throughput” is 360 cows per hour (3,600 seconds per hour divided by 10 seconds per stall = 360 cows per hour). However, theoretical throughput decreases if some cows ride around a second time, the parlor stops or a stall remains empty at entry. To account for these factors, a more realistic goal is 80 percent theoretical throughput, or 288 cows per hour in this example.

Step 3. Estimate labor needs

Rotation time also influences the amount of time your milkers have to perform a pre-milking hygiene routine, says Bill Bickert, agricultural engineer at Michigan State University. Remember, as the rotation speeds up, a milker will have less time to prep cows for milking.

Step 4. Calculate the number of stalls

A rotary should be sized so it is large enough to allow 9 minutes of available unit on-time per cow. And, it should allow about 90 percent or more of the cows to be milked out in one trip around the parlor.

Use the following example to help you determine the number of stalls needed if the rotation time is 12 seconds and each cow requires a unit on-time of 9 minutes:

Rotation time of 5 stalls per minute (60 seconds ÷ 12 seconds per stall = 5 stalls per minute)

x 9 minutes of unit on-time

= 45 stalls

+ 10 extra stalls*

= 55 stalls needed

* Assumes 3 stalls for pre-milking hygiene routine

+ 2 stalls to detach and post dip

+ 5 stalls for entry and exit

= 10 extra stalls

Thus, you need to install a minimum of 55 stalls in this rotary. If a cow enters the platform every 12 seconds, this parlor will milk a maximum of 300 cows per hour (3,600 seconds divided by 12 seconds per stall = 300 cows). However, if the parlor stops, cows ride around a second time or stalls remain empty, you can expect to milk less cows per hour. At 80 percent of theoretical throughput, expect to milk about 240 cows per hour in this example (300 cows x 80 percent = 240 cows).

**Many factors influence parlor efficiency**

A parlor’s size is not the only factor that influences its efficiency or cow throughput.

“A parlor must provide an environment that promotes quality milking, operator satisfaction, cow friendliness and consistency,” says Bill Bickert, agricultural engineer at Michigan State University. To help you develop a parlor with these qualities, consider these factors which contribute to a parlor’s efficiency:

- Parlor type.
- Level of mechanization.
- Cleanliness of cows.
- Production level of cows.
- Frequency of milking.
- Number of operators.
- Work routine.
- Operator skill.
- Parlor entrance and exit configuration.
- Cow grouping strategies.
- Future herd expansion.
- Arrangements for sorting and restraint.

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