Gene editing in breeding

Simulation analysis of breeding strategies for Sub-Saharan Africa dairy cattle production

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Abstract

Sub-Saharan African (SSA) dairy systems predominantly rely on local breeds with lower milk production potential; however, they still play a significant role in the SSA economy. Exotic breeds introduced to increase milk production often underperform due to their low heat tolerance and susceptibility to disease. A research project initiated by Acceligenâ„¢ focused on multiplex gene editing for heat tolerance, tuberculosis resistance, and trypanosomiasis to generate Holstein and Gir gene-edited lines. The project aimed to develop a high-yielding, heat-tolerant, and disease-resistant crossbreed dairy Holstein and Gir lines. Currently, Holstein and Gir edit lines are generated by Acceligenâ„¢ in Eagan, MN, and the next step is to cross-breed them to produce a synthetic breed called Slick Girolando and introduce to the selected study countries (Ethiopia, Kenya, Nigeria, and Uganda). The current study determined optimal breeding strategies through simulation analysis for sire lines over 20 generations and aimed to enhance economically important traits in SSA. The traits evaluated were milk yield, disease resistance, survival rate, reproductive performance, heat tolerance, and longevity. The simulated breeding population consisted of 132 females and 10 sires. Slick Girolando was used as the base population, and the sire line was exchanged according to the proposed strategies. All animals were assumed to be gene-edited to carry heat-tolerance and disease-resistance genes, which were inherited by subsequent generations. Four breeding strategies were evaluated: (1) crisscrossing Holstein-edited with Gir-edited sires (HG), (2) crisscrossing Gir-edited with Holstein-edited sires (GH), (3) modified crisscrossing strategies for Holstein-edited sires (HHG): use of Holstein-edited sires for two generations, then switching to Gir-edited sires for one generation, and (4) modified crisscrossing strategies for Gir-edited sires (GGH): use of Gir-edited sires for two generations, then switching to Holstein-edited sires for one generation. Restricted maximum likelihood (REML) was used to estimate genetic parameters and predict breeding outcomes for economically important traits and inbreeding. Variance components were estimated using REML, and breeding schemes were implemented and simulated with the lme4 in R software version 4.4.3. Visualization was with ggplot2, and sensitivity analyses were also conducted within R. The HHG modified strategy achieved the highest milk yield, reaching 5,720 kg per lactation by G20. In contrast, Gir-emphasized edited lines, especially GH and GGH, demonstrated stronger disease resistance and improved adaptation traits. Standard crisscrossing strategies generally outperformed others in reproductive performance, longevity, and survival. The HHG strategy reduced inbreeding over 20 generations. The sensitivity analysis identified that selecting a breeding strategy based on milk production was critical for the long-term success of dairy production in SSA. This study provided valuable insights into breeding strategies that can significantly enhance milk production and overall genetic improvement in SSA dairy production systems.

Keywords: 2026

How to Cite:

Gebeyehu, S., Heins, B. & Sonstegard, T., (2026) “Simulation analysis of breeding strategies for Sub-Saharan Africa dairy cattle production”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2286132. doi: https://doi.org/10.31274/wcgalp.23859

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