Equine

Inbreeding depression in racing performance of Coldblooded Trotters

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Abstract

The Coldblooded trotter descends from old, native horse breeds in Norway and Sweden and is primarily bred for racing performance. Intense use of popular stallions has led to a rapid increase in inbreeding, posing a risk of inbreeding depression. Managing inbreeding and keeping this numerically small breed healthy is important for animal welfare, owner economy, and the trotting industry's social license to operate. The aim of this study was therefore to estimate inbreeding depression in racing performance traits of Coldblooded trotters. Start status (whether a horse started or not as a three- to six-year-old) and inbreeding coefficients were available for a total of 63,781 Swedish and Norwegian horses born 1978-2020, of which 29,560 also had summarized performance records (earnings, record time per kilometre, and proportion of races with placings) as three- to six-year-olds, provided by the Swedish Trotting Association. The summarized performance traits were transformed to be approximately normally distributed, and the earnings were standardized within registration country and year. Inbreeding coefficients were estimated using the full pedigree, as well as seven ancestral generations, using the Pedig software. Linear mixed single-trait animal models including the interaction of birth year, country and sex as fixed effect, and inbreeding coefficient as a linear covariable, were used in the AIREMLF90 software to estimate the effect of inbreeding on performance traits and start-status. Inbreeding coefficient was also added as a quadratic covariable in preliminary analysis but was found nonsignificant. The mean pedigree completeness based on 7 ancestral generations varied from 85% for animals born in 1978 to above 99% for animals born after 2010. The generation interval based on foals born 1999-2018 was on average 11.4 years. The mean inbreeding coefficient for animals born in 2023 was 8.5% based on the full pedigree data and 5.9% based on 7 generations. The results showed significantly (P In conclusion, this study demonstrates inbreeding depression in racing performance and start status in Swedish and Norwegian Coldblooded trotters, confirming results from previous studies. The results are important for designing and communicating breeding measures to decrease the rate of inbreeding in the breed.

Keywords: 2026

How to Cite:

Eriksson, S., Berglund, P. & Berg, P., (2026) “Inbreeding depression in racing performance of Coldblooded Trotters”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2285763. doi: https://doi.org/10.31274/wcgalp.23787

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