Group Size

Herd and Group Sizing – Lactating Dairy Cows

Herd Size Constraints 

Beyond site permitting, water supply, nutrient management plans, and CAFO regulations, there are three major factors limiting herd size and expansion:

1. Manure storage capacity – can we store the manure from all of the cows for the required time interval?
2. Parlor capacity and throughput – is there sufficient throughput through the parlor to ensure that all the cows can be milked the desired number of times each day?
3. Holding area capacity – is there sufficient space for the cows in the holding area without the need to split groups?

Manure Storage Capacity

This is discussed under manure handling.

Parlor Capacity and Throughput

Most of the advice on parlor sizing is based on factors such as the number of milking stalls, the number of milkers, the preparation routine used, and whether or not automatic take-offs are used. These various factors influence the number of cows that may be milked per hour.

Cows milked per hour through a parlor depends on the parlor size as well as the number of milkers and the preparation procedures used (Reinemann et al.)

For side parlors (herringbone or parallel), a minimum of 4.0 turns per hour is suggested. A calculation of the parlor size required for a given number of milking cows is shown below:

1. Determine the desired hours per milking shift

E.g. Milking 3 times a day and assuming 1 hour of down time after each milking for clean-up, each shift would be 24-3 = 21/3 = 7 hours

2. Determine the desired cows per hour milked

Using the equation: # milking cows/hours per milking shift = desired cows per hour

E.g. For 1000 milking cows and a 7-hour milking shift: 1000/7 = 143 cows per hour

3. Determine the required number of milking stalls (side parlors only)

Using the equation: cows milked per hour/4.0 turns per hour = # milking stalls for side parlors

E.g. For 1000 milking cows and a 7-hour milking shift: 143/4.0 = 36 milking stalls or a Double 18

For rotary parlors, sizes typically range from 40 to 80 stalls with cows milked per hour ranging from 220 to 550 or more. In these parlors, throughput is dependent upon rotation speed which may vary from 6 to 20 seconds per cow.

Holding Area Capacity

The holding area is often located between the parlor and the cow barn, and is locked in size once it is built with little opportunity for expansion.

Therefore, we recommend building holding areas for 125% of the maximum group size with 20 square feet (1.9 sq m) per Holstein cow.

We suggest a minimum of 15 square feet (1.4 sq m) per cow for herds contemplating increasing group sizes who are unable to expand the holding area.

Group Size Constraints for Lactating Cows

Depending on the group of cows, lactating cow group size is determined by:

1. Herd size
2. Target duration of stay in each pen
3. Holding area capacity
4. Parlor capacity

Cows are most commonly grouped by age, production, or reproductive status.

Group size should not be limited solely by the size and design of the parlor, but by the maximum allowable time out of the pen spent milking each day.

In order to preserve time to allow cows to rest for 12 hours per day (h/d), the maximum amount of time spent out of the pen transferring to and from the parlor and milking should be 3 h/d. Time budget studies show that beyond this threshold, more time spent milking equates to less time spent lying down and resting.

Time budget for freestall housed dairy cows designed to preserve 12 h/d lying time

In general, parlor sizing does not take into account transfer time for cows to and from the pen, and this is reflected in the average of 90 minutes per milking time out of the pen, which has been identified in several large scale surveys of freestall housed dairy herds.

Rather than using the 4.0 turns per hour commonly used to estimate the size of the parlor required for a given herd size, we would set group size limits at a maximum of 3.8 turns per hour.

The table below gives suggested maximum group and herd sizes for a range of parlors, dependent on 2 or 3 times a day milking using 3.8 turns per hour as a maximum to account for transfer time.

Maximum group and herd size by parlor capacity

Since parlor throughput efficiency is likely less at 100 stalls (Double 50) compared to 60 stalls (Double 30) or less, we look at group sizes of ~150-250 as optimal in large herds over 1,250 cows.