Gene editing in breeding

Modelling the Influence of Juvenile Embryo Transfer Techniques on Genetic Gain in a New Zealand Dairy Breeding Programme

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Abstract

Embryo transfer (ET) technologies are widely used in cattle breeding programs to enhance genetic gain by increasing the reproductive output of elite donor cows. Juvenile in vitro embryo transfer (JIVET) collects oocytes from prepubertal females, enabling faster genetic progress by reducing generation intervals compared to trans-vaginal recovery (TVR) in post-puberty animals. This study uses stochastic simulation to examine the impact of JIVET on genetic gain in Livestock Improvement Corporation (LIC)'s New Zealand dairy breeding programme. Genomic evaluation was performed using LIC's across-breed platform with a custom single-step marker-based approach. Elite animals were selected based on estimated breeding values (EBVs), with inbreeding limits set for individuals and teams. The simulation utilised a single-breed nucleus scheme, initiated with a base population of 25,000 genotyped New Zealand Jersey cows and 1,000 sires. Pedigree relationships were retained, and a single trait with a heritability of 0.25-representative of milk production-was simulated across four lactations. A stochastic simulation was conducted over a 25-year horizon, with genetic gain estimated from the mean genetic merit of female progeny between years 15 and 25. Five scenarios were evaluated, described in Table1.: (1) BASE - reflecting current LIC practice including trans-vaginal recovery (TVR) embryo transfer (ET) and contract mating; (2) RSTR - the BASE scenario, including an additional 20% increase in embryo production via JIVET; (3) INBRD - the RSTR scenario without inbreeding constraints; (4) P-LIM, investigating a practical upper limit of JIVET by assuming a 163% increase in embryos from BASE; and (5) T-LIM - a theoretical upper limit of JIVET using the assumption of universal donor success resulting in a 544% increase in embryo yield. In scenarios BASE, RSTR, P-LIM, and T-LIM, inbreeding was controlled by preventing matings with pedigree coancestry above 6.25% and ensuring no bull sired more than 10% of an annual sire cohort. Each scenario was replicated 30 times to get stable scenario results (standard error < 0.005). As shown in Table 2., the BASE scenario produced an annual genetic gain of 0.354 genetic standard deviations with an average annual inbreeding rate of 0.295%. RSTR improved gain by 6% but raised inbreeding by 21%. Eliminating inbreeding constraints in INBRD increased the genetic gain to 7.4% - an additional 1.4% over RSTR - while inbreeding increased by 76% compared to BASE. P-LIM and T-LIM yielded gains of 9.2% and 13.6%, respectively, with moderate inbreeding increases. However, both scenarios needed more donors, embryo sessions, and better ET success rates than expected, leading to higher costs and reduced efficiency. JIVET-enhanced nucleus programs accelerate genetic improvement but highlight the importance of managing inbreeding, selecting suitable embryo donors, and considering ET technique success rates.

Keywords: 2026

How to Cite:

Donkersloot, E., Harris, B., Sherlock, R., Spelman, R. & Winkelman, A., (2026) “Modelling the Influence of Juvenile Embryo Transfer Techniques on Genetic Gain in a New Zealand Dairy Breeding Programme”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2285826. doi: https://doi.org/10.31274/wcgalp.23803

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