Crossbreeding in dairy cows – new breeding tools for more sustainable milk and meat production

Background

Crossbreeding has long been a natural part of breeding work in certain animal species, particularly pigs and poultry. Interest in crossbreeding dairy cows has increased in recent years, but pure breeding still dominates.

Breeding within breeds, especially within the Holstein breed internationally, has led to problems such as reduced fertility, poorer health, and shorter life expectancy in many countries. In some countries, such as New Zealand, crossbreeding has become a common way to avoid these problems. Breeding tools such as sex-sorted semen and genomic breeding values available at an early age, combined with the use of beef semen, offer new opportunities for crossbreeding in milk production.

About this project

The main objective of Julie Clasen's doctoral project was to study systematic crossbreeding and other breeding tools in Swedish dairy herds. Julie investigated the economic and genetic consequences of introducing crossbreeding between SRB and Holstein in an average Swedish herd in conjunction with the use of sex-sorted semen, beef breed semen, and genomic breeding values. Julie also studied a conservation strategy for herds with SKB where the least valuable cows are crossed with SRB.

In a survey, Julie asked Swedish farmers about their opinions on the use of sex-sorted semen, beef breed semen, genomic breeding values, dairy breed crossbreeding, and embryo transfer.

The final part of the doctoral project involved investigating a method for genomic breeding value estimation of crossbred animals using a summary of SNP effects if genomic data is not available for all breeds included in the crossbreeding.

Crossbreeding with SRB and Holstein improves the economic performance of the herd.

The first simulation study compared herd structure, production results, and economic results for herds with purebred cows and herds with crossbred cows. We used the SimHerd Crossbred simulation program for this. We examined both conventional and organic production, as the average results for cows and costs and revenues differ between these production systems. The simulation showed that the economic results for milk producers improve when switching from a purebred herd to a crossbred herd, and this applies to both conventional and organic production.

In a later simulation study, we used the results from SimHerd Crossbred to simulate the genetic development in the herd using the ADAM simulation program. The use of sex-sorted semen, beef semen, and genomic analysis of purebred animals increases the genetic level. If there are 30% F1 crossbreds, the genetic level in the herd decreases because the crossbred cows are produced from the genetically poorest cows in the purebred core. Despite this, the advantages of crossbreeding outweigh the genetic loss, and the overall economic result is better than in a purebred herd.

Crossbreeding could potentially preserve old cattle breeds

We also used SimHerd Crossbred to investigate how much the economic return could be increased in a herd of native cows (SKB) if 25% of the cows were crossed with SRB. As expected, there was a fairly large economic increase, but the increase was not sufficient to cover the economic support for purebred native animals from the state. Together with the marketing of niche products from native breeds, crossbreeding can contribute to the preservation of endangered breeds, as milk yield and slaughter yield can be increased from the herd and therefore preserve herds with these animals. However, this requires that the crossbreeding strategy be carefully controlled.

Farmers like different breeding tools

Our survey, conducted in the fall of 2020, showed that Swedish farmers have a strong preference for using sex-sorted semen and beef semen. When the survey was conducted, these tools were only used in 10-15% of all inseminations, which means that there was room to increase their use. Farmers were also positive about genomic analysis, provided that milk prices were not too unstable. When it came to dairy crossbreeding, there were two groups of farmers: those who liked dairy crossbreeding and those who were strongly opposed to it. Embryo transfer did not prove popular with farmers if they were to flush their own animals. However, they were neutral about purchasing embryos.

Genomic breeding evaluation of crossbred cows

When Julie wrote her thesis, there was no commercial breeding evaluation for crossbred animals in European countries. To date, there have not been enough genotypes from crossbred animals to enable genomic breeding evaluation. Another challenge is that many crossbred animals are three-way crosses of the ProCross type, and no country has access to data from all three breeds included in the ProCross system. The aim of the study was to find a method for genomic breeding evaluation that does not require genotypic information from the pure breeds in the reference population. Instead, the breeding value estimation is based on summary data on the different breeds.

Links

• Julie's doctoral thesis "Crossbreeding as a strategy in dairy cattle herds" (2021)
  
• Crossbreeding with dairy cows – effects on herd dynamics and economic performance
• Economic consequences of dairy crossbreeding in conventional and organic herds in Sweden
• Genetic consequences of terminal crossbreeding, genomic test, sexed semen, and beef semen in dairy herds
• Conservation of a native dairy cattle breed through terminal crossbreeding with commercial dairy breeds
• Multibreed genomic prediction using summary statistics and a breed-origin-of-alleles approach