In recent years, due to expansion and the end of quotas, herd size on farms has stabilised. Because of this, the amount of replacement heifers needed has changed.

Farmers can now increase the value of their calf crop by using beef sires, once enough heifers have been obtained of course.

The recommended replacement rate for a dairy herd is between 18-20%, so for a 100-cow herd that means 20 replacement heifers are required.

Replacement heifers

To achieve 20 replacement heifers entering the parlour in spring 2025, 47 cows and heifers need to be in-calf to a dairy sire at the end of breeding season - the use of sexed semen may reduce this number.

These cows should be served in the first three to four weeks of breeding.

Based on a slightly higher percentage of bulls being born, you should have 23 heifers calves born on the farm. Having 23 heifer calves allows for the birth of a freemartin or loss of a calf at birth.

This will results in 22 heifer calves suitable for breeding in May of 2024; again, you are allowing for one not going in-calf or replacing an extra cow.

This means that you should have 21 heifers calving down in the spring of 2025, giving you an extra cushion if something goes wrong.

Dairy-sired calves born in spring 2023 (bulls and heifers) 47
Heifers calves born in spring 2023 23
Heifers bred at 15 months (May 2024) 22
Heifers that calved in spring 2025 21
Heifers entering the parlour spring 2025 20
Calculating the replacements required for a 100-cow herd

The remaining 53 cows and heifers not in-calf to a dairy sire can then be served to a beef sire.

This means of the 77 potential calves that will be sold from the farm, 53 should be high value beef-sired calves.

Breeding season

To generate your replacements you should target your heifers, first-lactation cows and some second-lactation cows.

These should be the animals with the highest genetic merit within your herd, allowing you to accelerate genetic gain within your herd.

These animals should have higher levels of fertility, thus resulting in higher conception rates.