Choosing the right cows for breeding-Teagasc

Much time and effort is put into choosing the AI bull each year and rightly so; however, are you putting as much effort into choosing the right cows to breed from?

Ultimately, the bull is only half the story, and choosing the right cows is also vital. With a slowdown in herd expansion, and increased use of sexed semen, there is now scope to be more selective in the cows we breed replacement heifers from.

It is now very common to see surplus heifers being carried in herds each year, substantially increasing replacement costs. The target replacement rate for a stable herd size is 18-20%. Allowing for losses up to breeding, 22 dairy heifers born per 100 cows is a more appropriate target.

For an example 100-cow herd, all dairy semen sexed, aiming to have 22 dairy heifers born:

• 18 replacement heifers bred will produce 10 dairy heifer calves (18 heifers x 60% conception x 90% female); and,
• 27-30 sexed dairy straws will need to be used on the cows to produce the additional 12 dairy heifers required (12 calves required x 50% conception x 90% female).

As can be seen in the example above, only 27-30 sexed dairy straws are required to be used on the cows. However, where synchronisation or twice a day AI is not being carried out, it would be appropriate to select a slightly larger number of cows to have available for breeding replacements, as some cows will not be at the optimum breeding time when AI is taking place in this scenario, and should therefore not receive sexed semen. Even taking this into account, it is clear that less than half of the cows in the herd will be required for breeding replacement heifers.

Taking time now to identify the top 50% of your herd to breed from using Economic Breeding Index (EBI) and milk recording data will have a large positive effect on the genetic merit and subsequent performance of next year’s replacement heifer calves. The balance of the herd can be bred to high merit beef sires to produce saleable calves.

Keeping grass in the diet

The aim now must be to keep grass in the diet of dairy cows as much as possible during March. This month can be very costly where grass is not in the diet, as cow intake increases. Silage supplies can also run tight. Therefore, trying to graze is essential.

There are many reasons for this but primarily it is to:

• Increase milk price (higher fat and protein composition);
• Increase milk yield;
• Lower the cost of milk production; and,
• Grow more grass and increase grass quality in subsequent rotations.

When ground conditions are difficult, then practices have to be put in place to keep grass in the diet of the cow without causing serious damage to the land. These practices include:

• Grazing for a few hours after each milking;
• Using different entry and exit points to the paddock; and,
• Grazing lower covers of grass in difficult grazing conditions.

Source: Dairynews7x7 MArch 18th 2025 -The above article was prepared by Dr. Joe Patton, Head of Dairy Knowledge Transfer in Teagasc, and first appeared in the Teagasc Dairy Advisory Newsletter for March.