Breeding commenced on the farm on 18 April with 30 maiden heifers being synchronised for fixed time artificial insemination (AI). The 30 heifers remained indoors whilst on the programme and were turned out to grass this week, 14 days post insemination.

The main reason behind keeping the heifers housed up to this point was to try and maximise conception rates to fixed-timed AI. This was discussed with farm vet Donal Lynch, who said – from his previous experience – farmers who carry out AI indoors versus outdoors tend to achieve higher conception rates.

This is most likely put down to there being little or no environmental or dietary change for the heifers in the run up to breeding. When in a housed environment, the heifers do not have to deal with fluctuating temperatures from weather changes and the dry matter (DM) content of the feed does not change compared to grass during periods of rainfall.

The heifers were fed ad-lib 73% dry matter digestibilty (DMD) silage, 2kg of a high-energy 16% protein ration and ad-lib straw as an extra source of roughage. The heifers were given a mineral bolus and vaccinated for bovine viral diarrhoea (BVD) and leptospirosis one month prior to breeding also.

Fifteen heifers received conventional semen while the remaining 15 received sexed semen, with the programme for both being the same, apart from the timing of insemination. Heifers receiving sexed straws were inseminated eight hours later than heifers receiving conventional semen.

Heifers receiving sexed semen were picked on three main criteria: weight, dam performance and Eurostar index. Only heifers above 400kg are selected for sexed semen – it’s generally the heaviest heifers in the bunch that have the best chances of going in-calf to sexed semen due to heifers most likely having reached puberty well before insemination and likely have had two to three oestrus cycles before being bred.

That being said, the weight of a heifer doesn’t always determine how good her ability to breed future females for the herd will be, her mother must have a history of good fertility and milk ability for heifers to be selected. We also try to pick heifers with a high replacement index also. In theory, these heifers should breed better replacements than lower-index heifers.

The average replacement index of our 2024-born heifers is €142 so finding heifers with a suitable replacement index is not an issue, however, heifers that have a high index but are lighter than the desirable weight of 400kg or where dams have not had a history of going in calf to first service are not selected.

Table 1 outlines the synchronisation programme for heifers on Tullamore Farm.

Cows

Breeding in the mature-cow herd commenced on the 21 April, with 27 out of the 70 cows selected for breeding submitted for AI so far. The 2025 breeding season begins off the back of a successful calving season where 74 cows calved down with 75 live calves. There were two sets of twins born and one case of mortality.

Eighty eight per cent of cows calved unassisted. A successful calving season with a limited number of assisted calving sets the herd up for a good breeding season. However, the success recorded in the spring is a result of decisions made for the breeding season in 2024, with sexed semen being introduced and attention being paid to bull calving difficulty having positive effects.

A lot will remain unchanged for the 2025 calving season apart from more sexed semen being used. With the number of sexed semen bulls available increasing but still limited, the farm must be careful to avoid in-breeding with a history of these higher maternal bulls being used to breed for replacement heifers in the past.

Heat detection and timing

A vasectomised bull, fitted with a chin-ball harness is now running with the 30 maiden heifers at grass to pick up repeat services. Heifers have been tail painted and will be observed twice daily between days 17-24 post fixed-time insemination.

This is the second breeding season using heat detection collars on the cows and these have proved to be a major help in implementing the use of sexed semen.

The collar basically works as a ‘fitness tracker’ for cows, it tracks the cow’s activity, rumination levels and daily eating times.

A drop in rumination levels paired with increased activity will signal a heat. The cow is then assigned a heat index, indicating the strength of the heat and a 26-hour timeline is provided to indicate when each cow is suitable for either sexed or conventional semen.

A huge focus is being placed on sexed semen for the first month of breeding, meaning twice-a-day AI may be practised based on the given timelines to allow for best possible chance of conception.

For practicality reasons the farm will return to once-a-day AI in June and eligible cows will be given sexed semen and non-eligible cows will be given a terminal conventional straw. No cows will be offered sexed semen on repeat services.