The role of sexed semen and evaluation of fertility in Irish dairy herds. Dr. Stephen Butler and Dr. Stephen Moore
Teagasc, Moorepark Animal and Grassland Research and Innovation Centre, Fermoy, Co. Cork.
Motivation for sexed semen usage :
Sex-biased semen is a revolutionary technology that provides many potential advantages for the Irish dairy industry: 1. Replacement heifer requirements could be met using sexed semen in the first three weeks of the breeding season. Use of sexed semen instead of conventional semen would reduce the number of male dairy calves, which have poor beef traits and low economic value 2. Genetic gain for EBI could be accelerated by selecting the best dams to breed replacements 3. All dams that are not selected for breeding replacements should be inseminated with beef semen. This will help to increased the value of beef output from the dairy herd. The superior quality attributes of beef-cross calves relative to male dairy calves is vital for a sustainable beef industry 4. Dairy heifer rearing will be more streamlined, as all the female replacement animals will be born together within a short window of time at the start of the calving period; 5. Biosecurity can be improved by maintaining a closed herd.
Background
Research trials were carried out to evaluate the performance of sexed semen in lactating dairy cows in 2018 and 2019. During these trials, there was no sorting lab in Ireland, the trials were undertaken in collaboration with Irish AI companies, Cogent in the UK, and ST Genetics in the Netherlands.
The findings highlight large herd variation in conception rates achieved, and also the relative difference between conventional semen and sexed semen. This may indicate that decision rules regarding timing of AI is better suited to sexed semen on some farms compared with others.
2018 dairy cow field trial 1: Semen from both resident bulls (i.e. located at or near the sorting lab) and shipped ejaculates (i.e. bulls collected in Ireland, and ejaculates shipped to sorting lab within 6 to 7 h) were included in the study. Ejaculates were split and processed as either conventional semen (15m sperm per straw) or sexed (4m sperm per straw). Cows were inseminated after detected heats, and neither the farmer nor the AI technician was aware which straws were conventional semen and which straws were sexed semen.
2019 dairy cow field trial 2: A trial to evaluate the effect of timing of AI was conducted using semen from 3 bulls resident at Cogent. Ejaculates were split and processed as either conventional semen (15m sperm per straw) or sexed semen (4m sperm per straw). Enrolled cows were synchronised using a 10-day P4-Ovsynch protocol. 24 herds participated in the study, and each provided cows that were ≤4 parity and ≥50 days in milk on the day of AI. Cows within each herd were grouped based on parity and days in milk, and randomly assigned to one of 3 treatments:
In total, 7,236 inseminations events were analysed. The main findings were as follows: • Overall, conception rate was greater for cows inseminated with conventional semen than for those inseminated with sexed semen (59.9% vs. 45.5%; 76.0% relative to conventional semen). • The difference between conception rate achieved by conventional semen and sexed semen was less for resident bulls (60.3% vs. 50.2%; 84% relative to conventional semen) than for shipped ejaculates (58.6% vs. 40.7%; 70% relative to conventional semen). • In 33% of the herds, the conception rate achieved with sexed semen was ≥ 90% of the conception rate achieved with conventional semen.
1. 2. 3.
Conventional semen at 16 h after the final injection of GnRH (CONT) Sexed semen at 16 h after the final injection of GnRH (SEXED-16) Sexed semen at 22 h after the final injection of GnRH (SEXED-22)
Every herd was allocated an equal ratio of conventional and sexed semen from each of the three bulls. The main findings were as follows: •
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Conception rates were less in both sexed semen treatments compared with conventional semen (49.0, 51.3 and 61.1% for SEXED-16, SEXED-22 and