Use of parthenogenetic embryos to improve dairy-cow fertility following artificial insemination
Publication Date
July 30, 2026
Creator
Danielle Priestley
Abstract
Background: There is a need to improve conception rates to first service in high-yielding dairy cows, which is currently around 39% based on UK national records. In vitro produced (IVP) embryos or trophoblastic vesicles transferred one week after artificial insemination (AI) can improve pregnancy outcomes. However, the former increases twinning rates whilst the latter are laborious to generate. The production of parthenogenetic embryos (bPaEs), in contrast, is straightforward and can improve conception rates to AI in repeat breeder cows. The current study sought to determine the benefit of prophylactically transferring two bPaE 6-8 days following first service insemination on dairy-cow fertility.
Methods: Experiment 1 was undertaken on two commercial dairy farms in Devon, UK involving 256 Holstein-Friesian or Holstein-Friesian cross cows. Farm 1, autumn block-calving, grass-based system, milking 2x daily. Farm 2, all year-round calving with housed cows milked 3x daily. At AI, cows within each farm were paired according to parity, semen type (sexed vs unsorted), and randomly assigned to one of two treatment groups: AI (n=128), or AI + bPaE (n=128). Two IVP frozen-thawed bPaEs were transferred 6-8d following AI. Milk yield and body condition (BCS) were recorded, as was pregnancy establishment, determined by ultrasound at 30-40d gestation, and returns to oestrus. Pregnancy outcomes were analysed by logistic regression, and service intervals using general linear models (fitted terms in final models: ‘farm’, ‘days-in-milk; DIM’, ‘treatment’); data presented as means ± SEM.
Experiment 2 took place on a further two commercial dairy farms, one in Devon and one in Cornwall, UK involving 252 Holstein-Friesian cross cows. Farm 3, all year-round calving with housed cows milked 3x daily. Farm 4, autumn block-calving, grass-based system, milking 2x daily. Cows were enrolled if their first insemination was ≤70 days postpartum, but otherwise animals were paired with variables and outcomes recorded as per Experiment 1.
Results: Neither milk yield nor BCS affected fertility outcomes in either experiment. In Experiment 1 conception rates to AI alone increased (P = 0.007) with days since parturition on both farms (≤56d = 29.0±9.06; ≥70d = 57.7±6.74). Method of conception interacted with DIM to determine conception rate (P = 0.033), live birth rate (P = 0.020) and inter-service interval (P = 0.016) for those cows that returned to oestrus. Mean conception rates for bPaE v AI at ≤63d (i.e., date of transfer) = 45.8±8.84 v 27.0±8.22%; and at ≥77d = 59.6±7.00 v 62.8±6.25%. Similarly, mean inter-service intervals for bPaE v AI at ≤63d = 29.3±3.18 v 33.2±2.56 days; and at ≥77d = 29.9±2.26 v 24.9±2.21 days.
Experiment 2 revealed a 13-percentage point improvement in conception rate in the bPaE group, when AI occurred not after day 70 postpartum (P = 0.044). More specifically, the greatest advantage could be seen in primiparous cows, where mean conception rates for bPaE v AI at ≤77d (i.e., date of transfer) = 69.4±8.1 v 31.1±8.45% (P = 0.002). Mean birth rates for bPaE v AI of primiparous cows at ≤77d = 63.1±8.45 v 30.2±8.52% (P = 0.008). Inter-service interval was unaffected by treatment.
When data from primiparous cows inseminated ≤70d from both experiments was combined and analysed alone, bPaE treatment increased conception rate (P = 0.002) and live birth rate (P = 0.008), while inter-service interval and survival rates beyond day 40 remained unaffected.
Conclusions: Transfer of bPaE during the early postpartum period (≤ 77 days postpartum), when fertility is low, improves pregnancy rates to AI and does not adversely affect inter-service intervals for cows returning to oestrus. This effect is most notable in primiparous cows. In contrast, the transfer of bPaE beyond 77 days postpartum, when fertility is higher, reduces pregnancy rates to AI and delays returns to oestrus by around one week on average.
Item Type
ethesis
Thesis Type
MRes
Supervisors
Sinclair, Kevin
University of Nottingham
University of Nottingham
Subjects (LC)
Associated Schools / Departments
UoN Repository URI
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