BREEDING ▶▶▶


Breeding for improved fertility


A dairy farm begins with a calf, and satisfactory female fertility is therefore an important part of any dairy business. A cow needs a calf periodically to be able to re-start lactation and continue milk production while heifer calves are also needed to replace older cows.


BY LARS PETER SØRENSEN, GENETIC DEVELOPMENT MANAGER, VIKINGGENETICS M


anagement strategies relating to the replace- ment of culled cows have changed over time. To- day, many dairy farmers use sexed semen to pro- duce replacement heifers from the best cows/


heifers and use conventional semen, usually in combination with beef semen for the remaining cows. From a financial point of view, this is very favourable as cow longevity is improving, which means cows have a longer use- ful life and the need for replacement heifers is lower than it used to be. What’s more, many dairy farmers now realise that it is expensive to raise heifer calves both for their own use and for selling.


Nordic countries In the Nordic countries breeding for improved fertility has been taking place for more than 40 years. Even before the Nordic Cattle Genetic Evaluation (NAV) or VikingGenetics was created, breeding values for fertility have been calculated in the Nordic countries. In the 1980s and 90s, the target was very much about in- creasing milk production which meant imported semen, mainly from North America. Due to the negative genetic cor- relation between milk production and female fertility this led


Table 1 – Number of VikingGenetics (VG) bulls on the Interbull top 20 list for fertility and NTM.


Breed


Holstein 6 Jersey 12 Red breeds


1 Source: Nordic Cattle Genetic Evaluation (NAV) 8 ▶DAIRY GLOBAL | Volume 7, No. 1, 2020


Fertility, number of bulls in top 20 NTM, number of bulls in top 20 7


17 20


to a decline in fertility, phenotypic and genetic, which soon became a practical problem on dairy farms. Breeding strategies were then changed so that more bulls were selected from pedigrees with an increased focus on fertility and at the same time avoiding some international pedigrees with poor fertility-related performance. The effect of this change was most evident in Holstein cows where a rapid increase in the genetic level has been observed up until today. A similar trend can also be observed in Jersey cows and the red breeds but at a lower level because these in general have better fertility than Holsteins. Figure 1 shows genetic trends in fertility in Holstein cows, based on the Interbull fertility index. Shown here is a compar- ison of Nordic (DFS) bulls with bulls from other countries. The effect of the change in breeding strategy for fertility men- tioned can be clearly seen from the year 2000. The trend is similar for all countries, but the Nordic Holstein bulls remain at a higher genetic level. Given the VikingGenetics share of the Holstein world population our bulls are performing very well. For Jersey bulls, the main competitors regarding fertility are New Zealand bulls. However, eight of the ten highest ranking bulls for daughter pregnancy rates in the United States of America (US) are still VikingGenetics bulls. In the case of the red breeds, the list is dominated by Nor- wegian bulls, however for the Nordic Total Merit (NTM), the list is totally dominated by VikingGenetics (VG) bulls.


Accurate breeding values With regards to fertility, it is easy to conclude that Viking- Genetics’ bulls are highly sought after on the world market. The reason for this success is very much the focus on fertility. For example, for Holsteins the weighting given to fertility in the Danish total merit index, the S-index, was 0.18 in 1989, later it increased to 0.26. When NTM was introduced in 2008 the weighting for fertility was increased to 0.41. This was sub- sequently adjusted to 0.36 in 2019. Accurate breeding values for fertility are the key to achieving big genetic progress in fertility. The Nordic countries have a long tradition of extensive and accurate registration of insem- inations. This includes collecting registrations and insemina- tion of each bull planned for an insemination, together with accurate recording of dates and calving, registration of repro- ductive disorders, elimination of genetic defects etc.


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