Joe Kelleher: How many replacements do we need?

Stock image.
Stock image.
Joe Kelleher

Joe Kelleher

There has been a lot of focus this spring on improving the beef traits of the non-replacement calves produced from the national dairy herd.

The key recommendations include using sexed semen, using more beef AI, using the dairy beef index to choose bulls, and only generating enough heifers to meet your replacement requirements. But how many replacement heifers are required on your farm?

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There are numerous factors that will determine the number of replacements required on our dairy farms; the fertility status of the herd, the age profile, disease status, calving spread, expanding herd or static, farmers' own desire to improve the genetics of their herd.

The list goes on. Having assessed all these factors, every farmer should have an idea of the number of heifer calves they wish to see on the ground in spring 2020.

When you know the number of heifer calves you want, you can then start to plan how many cows you need to serve to dairy sires. To illustrate the point, the table below goes through an example for a 100-cow herd.

The starting point for this exercise is to enter the number of heifers you want in the parlour in spring 2022. In this situation, the farmer is not expanding and has an empty rate typically of 10pc.

Therefore, 10 heifers are required to replace those that do not go back in calf. She/he also wishes to cull a few late calvers and to allow room to replace some lame cows, high SCC cows and low protein cows, so she/he has decided that a further 10 heifers will achieve this.

To achieve 20 heifers successfully standing in the parlour in 2022, this farmer has decided they need to calve down 21 heifers to allow for the one heifer that may calve down with blind quarters or may meet some other fate at calving.

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To calve down 21 heifers, they decide they need to breed 22 heifers to allow for the one that won't go in calf, and to have 22 heifers for breeding, they decided they needed 23 dairy bred heifer calves born to allow for the one that might die at birth.

Nationally, 49pc of the calves that are born are heifers versus 51pc bull calves, although there can be big variations between farms. In this situation, we will allow for a slightly higher bull-to-heifer ratio, which means this farmer needs to target putting 96 cows in calf to dairy bulls.

This works out at just shy of five straws/natural serves to get one calf on the ground. Fertile herds may get away with 4.5 straws, whereas infertile herds may have to use 5.5 straws/serves to achieve an adequate number of replacements.

Sexed semen can be used to reduce this figure, but as many of you are now two to three weeks into the breeding season, the window for using sexed semen now has probably passed.

Fertile herds that only use dairy sires on the cows (and run a beef bull with the heifers) will need to use dairy sires for a minimum of four weeks on all cows to achieve the previous figures.

Where herd fertility is poor, this may need to be extended to six weeks. Herds that breed both heifers and cows to dairy sires have the choice of either reducing the length of the breeding season or by being selective on which cows they choose to breed (only if using AI) to dairy sires, leaving the option of using high beef merit sires on cows you would rather not breed a replacement from.

From a national perspective, improving the quality of the beef produced from the dairy herd is important, but so is producing an adequate number of dairy replacements. It is important to get balance right on your farm. Do a few quick sums and work out when you can afford to switch to beef sires.

Joe Kelleher is a Teagasc advisor based in Newcastle West, Co Limerick

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