Breeding goals & design

Development of a nucleus selection index for selection within elite breeding programs

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Abstract

Commercial selection indexes aim to maximize economic output in commercial herds by ranking animals based on expected profitability. In contrast, nucleus breeding programs prioritize generating elite progeny, ranked on the commercial selection indexes, for genetic advancement and marketability. Within a nucleus breeding program, commercial index values become abstract because their original economic basis is no longer relevant, as they instead serve as numerical selection targets rather than reflecting the true economic realities. This work focuses on the development of a nucleus selection index, that emphasizes the economic realities within a nucleus breeding program. Different levels of genetic progeny have different monetary values to elite breeders following a non-linear relationship with the abstract commercial index value. In a beef cattle breed such as Angus, bulls can be separated into groups such with the highest value being the very best bulls (top 50-100 born in a year based on the commercial indexes) that can be used to produce both the marketed AI bulls and the next generation of mating sires and donors, bulls with genetic value high enough to be utilized as an AI sire in commercial herds, and those that could be utilized as jumper bulls, but unable to realistically produce the breed best progeny. The value drops sharply from the best animals to those with more limited commercial use. Females may also be classified into distinct groups according to their genetic capacity to realistically produce offspring within these categories, as well as their embryo marketability, and follow a similar non-linear relationship with the abstract commercial index values. The nucleus index is calculated by determining the likelihood an animal can produce each of the specific progeny categories, within one or multiple indexes, and then multiplying those probabilities by the monetary value of each of the progeny categories. These are then summed and multiplied by the expected number of progeny the animal would produce within the nucleus breeding scheme, accounting for reproductive rate and any limits due to diversity requirements. As the likelihood of producing progeny of specific categories is dependent on both other animals in the population and genetic trends, these values need to be updated frequently to account for younger animals entering the breeding pool. Costs associated with creating the progeny can be included as well. As within the commercial selection index, these values from the nucleus selection index provide estimates of the profit that each animal will return given the specific economics of the elite breeding program.

Keywords: 2026

How to Cite:

Bjelland, D., Quinton, C., Hely, F., Crowley, J., Byrne, T. & Amer, P., (2026) “Development of a nucleus selection index for selection within elite breeding programs”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2295741. doi: https://doi.org/10.31274/wcgalp.24368

Rights: 1