Importance of purebreeding and conservation of native breeds . 58

It is essential to maintain purebred lines for the benefit of genetic gain and heterosis in crossbreeding. The parental breeds need to be economically equivalent if crossbreeding is expected economically superior (Freyer et al.

2008; Sørensen et al. 2008), and therefore they need to improve simultaneously. The numerically largest dairy breeds in the Nordic countries, are economically equivalent (Stålhammar 2014; Kargo et al.

2020) – at least for now. Statistics in Swedish dairy cattle show that the SH is currently improving in milk yield, reproduction, and health traits – and

improving faster than SR (Växa Sverige 2019, 2021) – meaning that if this trend continues, the SR and crossbreds between SH and SR will no longer be economically competitive to SH in the future. The study in paper II showed that crossbreeding was no longer economically beneficial if the relative ratio in milk yield between the two breeds went below 0.92.

Nevertheless, crossing Holstein with SR may be a way to keep SR attractive on the international market, if not the Swedish.

Using crossbreeding as a strategy for the conservation of breeds needs to be carefully managed but can potentially turn out successfully (Verrier et al. 2005; Lambert-Derkimba et al. 2019). It has already been decided globally (UN 1992; FAO 2007) and nationally (Swedish Board of Agriculture 2009) and nationally that native livestock breeds should be conserved for sustainable and cultural reasons. Governments are paying farmers to keep the native breeds and breed them according to breeding plans (Swedish Board of Agriculture 2021). Nevertheless, the native breed populations are still decreasing in size, at least the Swedish native cattle breeds, and therefore calls for other conservation strategies.

In the future, more economic emphasis may be put on the milk composition instead of the quantity of fat and protein, which is the current situation in the Nordic countries. Some native dairy breeds carry high frequencies of favorable alleles for cheese production, such as the kappa-casein A2-allele and beta-kappa-casein B-allele (Petrovska et al. 2017; Poulsen et al. 2017). There is also evidence that the fatty acid and mineral composition in milk from some native dairy breeds is more healthy for human consumption, compared with e.g., Holstein (Gottardo et al. 2017; Poulsen et al. 2020). These properties of native cattle breeds are worth considering in creating a niche market of locally produced dairy products. Those favorable milk alleles also exist in modern dairy breeds (Gustavsson et al.

2014; Poulsen et al. 2016; Chessa et al. 2020), and therefore crossbreeding native breeds with modern breeds may improve the yield of niche products (Saha et al. 2017) if modern AI bulls used also carry the desired alleles.

There is also a great potential for utilizing GT and select cows and bulls based on desired alleles.

Genomic selection can be a valuable tool for improving also small cattle populations (Hozé et al. 2014; Thomasen et al. 2014; Schöpke & Swalve 2016; Karaman et al. 2021), and exploiting information on crossbred animals may even be a key to conserve the local breeds (Stock et al. 2021).

5.8 Farmers’ perception of crossbreeding

The study in paper I revealed that dairy farmers could (roughly) be divided into two groups: those supporting crossbreeding and those not supporting it. Believing that crossbreeding threatens the pure breeds is valid, especially for breeds from a small or decreasing breed population, such as SR. Unlike poultry, beef, or sheep breeders, dairy farmers tend to be more personally attached to their animals (Bock et al. 2007), which probably makes them more attached to animals with specific characteristics (breeds). Thus, introducing a new breed or crossbreeding may be considered a significant change for dairy farmers.

In France, farmers who changed to crossbreeding had to ‘stand on their own feet,’ giving up on breeding advisors and genetic merit indices, and basically, they had to ‘figure it out’ by themselves (Ollion et al. 2018;

Quénon et al. 2020; Magne & Quénon 2021). Some farmers even indicated that the feeling of being ‘locked into a system’ and following ‘mainstream’

purebreeding and following specific breeding goals led them to consider crossbreeding. Furthermore, breeding associations, advisors, and public research institutions showed limited support for crossbreeding (Magne &

Quénon 2021). Farmers did not seem to be giving up on breeding advisors in our study in paper I, but since none of them had herds of entirely crossbreds, it is unknown if they only used the breeding advisors for purebreeding. Several negative comments from the respondents about the breeding goal and selection of bulls in the Nordic countries could reflect a

‘locked in’ feeling. Thus, more support from breeding advisors and breeding companies may motivate more farmers to consider crossbreeding.

In paper I, more of the responding farmers in the CROSS group had used or tried SS, BS, and GT than the average of all respondents (Table 4), suggesting that farmers using crossbreeding may be more open-minded to try various breeding tools. It supports the findings from the French studies that farmers using crossbreeding dared to change breeding strategy without the support from breeding advisors (Ollion et al. 2018; Quénon et al. 2020;

Magne & Quénon 2021).

¾ Swedish dairy farmers can be divided into two groups: those supporting dairy crossbreeding and those against it.

¾ Swedish dairy farmers who have tested dairy crossbreeding seem to be more interested in using sexed semen, beef semen, and genomic testing

¾ Terminal and rotational crossbreeding strategies between Swedish Holstein and Swedish Red are economically beneficial in average Swedish conventional and organic dairy herds

¾ Terminal and rotational crossbreeding strategies between Swedish Holstein and Swedish Red reduces the number of replacement heifers, compared to a herd having purebred Swedish Holstein.

This gives opportunities for reduced costs of keeping young stock in the herd and potentially a reduced environmental footprint from the dairy herd

¾ The economic benefits of terminal crossbreeding can be improved by combining the strategy with the use of sexed semen, beef semen, and genomic testing

¾ There is an economic potential for dairy farmers of using terminal crossbreeding as a conservation strategy, although it may not be economically beneficial for the government. Crossbreeding alone cannot compensate for the economic gap between native and modern breeds

¾ In the situation where sharing of genotype and phenotype data from different breeds is impossible, the use of summary statistics can yield accuracies on genomic prediction for crossbred animals almost as high as having full data available