Kinship and inbreeding in the Dutch Fjord population analyzed

Published on
February 17, 2022

At the moment the inbreeding rate in the Dutch Fjord population is not alarming, but vigilance is necessary in order to keep the status quo. The inbreeding rate is now below 0.5% per generation. An inbreeding rate between 0.5% and 1% requires strict monitoring and a rate of >1% requires additional management to reduce the rate of inbreeding.

Prospects of inbreeding in future generations are shaped by the kinship of the parents, and the rate of kinship within the Fjord population is currently >1%. Consequently, it is recommended to limit the increase in kinship. These are the conclusions drawn from a studbook analysis performed by student Marjorie Byrne of Wageningen University & Research, Animal Breeding and Genomics, supervised by researchers Harmen Doekes and Jack Winding.

Kinship and inbreeding rates in the Dutch Fjord population

To keep a population genetically healthy, it is recommended that the inbreeding rate should be kept below 1% (or preferably below 0.5%) per generation. In the Dutch Fjord population, the inbreeding rate, estimated for periods of 10 years, has been below 0.5% per generation almost continuously (Table 1). However, at the moment the average kinship rate in the Dutch Fjord population is increasing with more than 1% per generation (!). Since the kinship of the parents determines the inbreeding of the offspring, we can expect a (substantial) rise in inbreeding rate in the near future. Therefore, the advice is to take actions to limit the kinship rate at population level, alongside the current mating restrictions.

Table 1.

Inbreeding and kinship rate per generation for periods of 10 years.

Period Inbreeding rate (%) Kinship rate (%)
1950-1960 -0.20 -0.65
1961-1970 0.48 1.48
1971-1980 0.53 0.35
1981-1990 0.48 0.37
1991-2000 0.26 -0.52
2001-2010 -0.33 0.55
2010-2019 0.36 1.04

How can we reduce kinship rate?

One option to reduce the kinship rate (and, consequently the inbreeding rate) is to set so-called “sire restrictions”. In other words, to set a limitation to how often a stallion can breed. However, if a stallion that has reached its limit is consequently replaced by a close relative (e.g. a son or a brother), the inbreeding rate will still rise rapidly. An alternative option is “mean kinship selection”, where the average kinship of each breeding-candidate is calculated with all the other breeding-candidates and breeding-candidates with a high average kinship are excluded from breeding. This is one of the most effective methods to reduce kinship rate and it has been successfully implemented for several dog breeds.

In conclusion, it is recommended to take actions to reduce kinship rate within the Dutch Fjord population. A quick intervention will prevent a steep rise in inbreeding rate and forestall the need for more drastic measures.

De data Data for this research was provided by the Dutch Fjordhorse Association.