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Department of Dairy Science, University of Wisconsin, Madison 53706
E-mail: weigel{at}calshp.cals.wisc.edu.
The availability of sexed semen in dairy cattle has been eagerly anticipated for many years, and recent developments in fluorescence activated cell sorting have brought this technology to the brink of commercial application. Two limitations still exist, namely sorting speed (hence, availability and price) and in vivo conception rates. Presently, about 150 to 200 straws of X-bearing sperm can be sorted per machine per day, and this comprises less that 0.5% of the daily domestic dairy semen requirement. Furthermore, conception rates in field trials involving virgin heifers have typically ranged from 35 to 40% with sexed semen, as compared with 55 to 60% for unsexed semen, and this limits the willingness of producers to pay a premium price for the product. The focus of this paper is to discuss 3 potential breeding schemes that can lead to widespread usage of sexed semen today, in spite of its aforementioned limitations. The first strategy, earlier (than normal) breeding of virgin heifers with sexed semen, followed by the use of unsexed semen for repeat services, would provide 62 to 66% female offspring at first calving with no detrimental effects on average age at calving or dystocia. Semen cost per heifer calf would increase by $47 to 56, $123 to 137, or $199 to 217, depending on conception rate, for sexed semen priced at $50, $100, or $150 per unit, respectively. The second strategy, in vitro embryo production using known donors with dairy heifers as recipients, could provide extra heifer calves at an added cost of $81 to 118 or $212 to 286 for female embryos costing $50 or $100, respectively. The third strategy, in vitro embryo production with anonymous donors and beef recipients, could increase net calf value per recipient by $52 to 97 (single transfers) or $171 to 240 (double transfers) for embryos costing $25 each and by $11 to 59 (single transfers) or $95 to 161 (double transfers) for embryos that cost $50. Thus, strategies exist for near-term application of sexed semen within the routine management of commercial dairy farms. Early adopters of this technology will capture economic benefits associated with extra replacement heifers, as well as enhanced biosecurity via the ability to expand rapidly from within a closed herd.
Key Words: sexed semen • replacement heifer • embryo transfer • in vitro production
Abbreviation key: ET = embryo transfer, IVP = in vitro embryo production, MAS = marker-assisted selection, MOET = multiple ovulation and embryo transfer
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