Photo: Shutterstock Kinship and inbreeding in Holstein Friesian bulls have been increasing fast in recent years, PhD student Harmen Doekes has ascertained. Thanks to targeted pairing, inbreeding among the cows has not increased so much. He advises safeguarding genetic diversity.
Most of the dairy cows in the Netherlands are of the Holstein Friesian breed. Livestock farmers use a select group of AI bulls that produce calves with useful traits. Doekes studied kinship and diversity among AI bulls born between 1986 and 2015, using DNA markers.
Genetic progress
Inbreeding is problematic if it happens at the expense of the productivity and health of the cows. That is then known as inbreeding depression. The level of inbreeding depression is negligible at the moment in comparison with the genetic progress, says Doekes. Through the genetic progress, today’s cows produce more milk, are more fertile and have healthier udders than the cows of 10 to 20 years ago. ‘I also saw that expanding the breeding goal around the year 2000 reduced inbreeding. Until then, breeders focussed mainly on the milk yield. Since 2000, more traits, such as fertility and health, have been added to the breeding goal.’
DNA markers
Diversity still deserves attention, says the PhD student, now that it has become clear that kinship and inbreeding have increased faster in the past 10 years. He established the kinship between the bulls with the aid of 75,000 DNA markers. This method is more precise that the old calculation method using a pedigree. ‘With a pedigree, you assume that a calf gets 50 per cent of its genetic material from the father and 50 per cent from the mother, but you don’t know exactly which 50 per cent. With DNA data, you do know this and you can pinpoint kinship and inbreeding more precisely.’
Top bull
In this era of genomics, breeding organizations would sooner select calves on the basis of DNA information, says Doekes. ‘That way you get more genetic progress and there is more competition to get a top bull in the short term. That partly explains why inbreeding is increasing fast.’ He advises breeders to monitor kinship and inbreeding at the DNA level and to limit it through their selection of bulls.
Doekes graduated on 18 September with a PhD supervised by Roel Veerkamp, professor by special appointment in Numerical Genetics.