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Weigh heifers before opting for sexed semen

Weigh heifers before opting for sexed semen

Earlier housing and a delayed turnout may mean that some dairy replacement heifers are behind target for breeding.

Joining James Dunne on a recent episode of the Dairy Edge podcast, Teagasc Dairy Specialist, Stuart Childs touched on the ramifications this may have for the fast-approaching breeding season, especially where a sexed semen programme is being planned.

As a technology, sexed semen usage has grown in popularity on farms nationally, with many targeting it towards maiden heifers following a synchronisation programme. However, as Stuart explained, to maximise conception rates heifers must be at target weight for breeding.

“The best barometer of stock performance is weighing,” Stuart explained. Giving an example of the desired target weights for replacement heifers ahead of breeding, he said: “The average maintence sub-index in the country is €13 and that means the average cow in the country is 576kg. We always talk about 60% of mature weight for breeding at 15 months, that’s bringing you to 345-350kg. People need to have the heifers hitting that target.”

Table 1 below provides details on the projected liveweight of mature cows, based on their maintence index value, and the 60% target weight for heifers at breeding.

Table 1: Maintenance Index value (€) and the associated projected live weight (kg)

Maintence Index (€)Projected liveweight (kg)Breeding weight target at 15 months (60% of projected liveweight)(kg)
-10 691 415
-5 666 400
0 641 385
5 616 370
10 591 355
13 (national average) 576 346
15 566 340
20 541 325
25 516 310
30 491 295

Where heifers fail to meet this 60% target, their reproductive performance is limited, with Stuart adding: “The big concern around conception rate here would be the use of sexed semen on underweight heifers. There is a risk that they are just not going to be at top gear in terms of reproductive performance and you’re putting a very expensive product into an animal that is almost borderline destined to fail.”

On what farmers should do if they are concerned, Stuart said: “Weighing the heifers is the most important thing and then make the decision if they are suitable for sexed or conventional semen.”

Delaying the start of breeding

With heifers being behind target, some farmers may be tempted to delay the start of breeding, allowing heifers more time to grow or catch up; but Stuart advised against this.

“If you delay [the start of breeding] for three weeks and they don’t go in calf, they are now six weeks later than what you originally planned.

“If they are just marginally off target, I think you err on the side of caution in terms of steering away from sexed semen because of the cost of it, go with your conventional, AI them as planned and stick to the plan [on breeding start date].

“The solution to the problem isn’t moving the date of AI. The solution to the problem is getting the stock to target weight in future years.”

For these heifers that are slightly behind target at turnout, Stuart recommended supplementing them with 2kg/head/day of concentrate at grass to boost weight gain ahead of the breeding season, adding: “If they are off target, turn them out, continue to feed them and don’t change the plan, get them bred.”

However, where heifers are severely under target weight, Stuart said farmers have decisions to make, adding: “If they are extremely underweight, the likelihood that they are cycling is limited. Their reproductive performance is severely compromised by the fact that they haven’t hit their target weight in the first place. You might even be saying that these heifers aren’t suitable for breeding.”

For more advice on turning heifers out to grass and synchronisation protocols, listen to the Dairy Edge podcast below: