A 100-cow herd in 2013 could expand to 530 cows in nine years with the help of fresh-sexed semen, say Teagasc researchers.
The benefit of sexed semen in the Irish dairy industry is the increased numbers of heifer calves born, with 90% of successful pregnancies resulting in a heifer calf.
The increased availability of replacement heifers could be a pivotal component of the 50% increase in milk output targeted in the Food Harvest 2020 strategy.
The researchers assumed conception rates in heifers at 70% for conventional frozen-thawed semen, 66% for fresh-sexed semen, and 53% for frozen-thawed sexed semen.
They estimated herd expansion for maiden heifers, using sexed semen for the first and second services. From 100 cows in 2013, using conventional frozen-thawed semen could take numbers to about 220 in 2022. Numbers could increase to 245 with frozen-thawed sexed semen; 300 with fresh-sexed semen.
They also looked at using sexed semen on heifers, and also on lactating cows inseminated in the first six weeks of the breeding season.
Conception rates in lactating cows are assumed to be 50%, 47% and 38% for conventional, frozen-thawed, fresh-sexed and frozen-thawed sexed semen, respectively.
In this case, from 100 cows in 2013, using conventional, frozen-thawed semen could still take numbers to about 220 in 2022. But numbers could go to 330 with frozen-thawed sexed semen; and 530 with fresh-sexed semen (about 350 cows by 2020).
Researchers visualised that in 2013 and 2014, 20 replacement heifers would be retained to maintain a herd size of 100 cows. Thereafter, all available heifers were retained for herd expansion.
The mating start date was assumed to be Apr 25 every year. Mean herd calving dates every year would be Mar 1 for both conventional frozen-thawed semen and fresh-sexed semen, and Mar 2 for frozen-thawed sexed semen, when only maiden heifers are inseminated with sexed semen. When sexed-semen use is extended to include lactating cows, mean herd calving dates are Mar 1, 2 and 7 for conventional, frozen-thawed, fresh sexed and frozen-thawed sexed semen, respectively.
Use of sexed semen could have other beneficial effects:
* Reduced incidence of calving difficulty (because heifer calves are smaller than male calves).
* Improved biosecurity by allowing farmers to increase herd size, while maintaining a closed herd.
* Reduced numbers of low-value male dairy calves born.
* Male offspring from easy-calving beef bulls after the first six weeks of breeding to generate higher value male calves for beef.
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