by Kyle Mathews

Many in the industry will admit that we’re much more efficient at raising calves and heifers now than even 10 years ago, which has led to many dairy producers having a surplus of replacement animals, causing overcrowding in heifer pens. In any dairy climate, raising more heifers than your dairy system needs is a financial strain that needs to be evaluated. Imagine you have 20 excess heifers per year on your farm, and that average cost per day is $2.00 per animal. That’s a $14,600 expense that you may not have needed to incur.

First, ask yourself a few questions. Are you planning on expanding, shrinking, or maintaining the herd? What is your herd size (milking and dry) going to be? What is your average age at first calving? What is your herd cull rate? What is your non- completion rate on heifers? (Percentage of heifers born that do not enter the milking herd, including still birth and other mortality). Once these questions are answered, the following formula can be used to show how many heifers you need annually to maintain herd size.

Herd Size X (Age at First Calving in Months/24) X Cull Rate X (1+Non-Completion Rate) = Annual number of Heifers Needed.

Here’s an example for a 500 cow dairy planning on maintaining herd size, with a 23 month age at first calving, a cull rate of 35%, and a Non-Completion rate of 10%:

500 X (23/24) X 0.35 X (1+0.10) = 184 Heifers Annually

This does not however give you the entire picture. We also need to know how many heifers you normally have on a yearly basis, so we can estimate how many heifers per year you can sell to maintain your herd size. We will need to know herd size, calving interval, percentage of calves born that are heifers, heifer mortality rate, and age at first calving. Once these are determined, the following formula can be used to project how many heifers you would have in a year’s time:

1 X Herd Size X 12 / Calving Interval X Percentage of Heifers X (1-Heifer Mortality) X 24 / Age at First Calving = Number of Heifers Per Year

Here’s an example for that same 500 cow dairy, with a calving interval of 13 months, 55% of calves born are heifers, and total calf mortality of 10%:

1 X 500 X 12/13 X 0.55 X (1-0.10) X 24/23 = 238 Heifers annually

This means that there are 54 heifers per year that the farm now must decide what to do with. Do you freshen them in and cull mature cows? Do you grow the herd? Or do you sell excess heifers? This is a question that is not easily answered. Ag Partners is more than happy to sit down and discuss these items further with you!

Source: University of Wisconsin-Extension