Breeding for improved fertility for over 40 years

By Lars Peter Sørensen, Genetic Development Manager, VikingGenetics

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.

Management strategies related to the replacement of culled cows have changed over time. Today, many dairy farmers use sexed semen to produce 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 positive as cow longevity is improving, which means cows have a longer useful life and the need for replacement heifers is lower than it used to be. What´s more, many dairy farmers now know that it is expensive to raise heifer calves both for their own use and to sell.

In the Nordic countries, we have been breeding for improved fertility for more than 40 years. Even before the Nordic Cattle Genetic Evaluation (NAV) or VikingGenetics were created, breeding values for fertility were being calculated in the Nordic countries. 

In the 1980s and 90s, the target was very much about increasing milk production, which meant imported semen, mainly from North America. Due to the negative genetic correlation between milk production and female fertility, this led to a decline in fertility, both 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 where a rapid increase in genetic level has been observed until today. A similar trend can be observed in Jersey and the red breeds but at a lower level because these have better fertility in general than Holstein.

Figure 1 shows genetic trends for fertility in Holstein, based on the Interbull Fertility Index. Shown here is the comparison of Nordic (DFS) bulls with bulls from other countries. The effect of the change in breeding strategy for fertility mentioned 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.
 
Figure 1: How VikingGenetics bulls compare with bulls from other countries. 
DFS = Denmark, Finland, Sweden
Source: NAV: Nordic Cattle Breeding Evaluation 
From a VikingGenetics point of view it is also important to know how VikingGenetics bulls compare with bulls from other countries. 
Accurate breeding values for fertility as a target 

With regard to fertility, it is easy to conclude that VikingGenetics bulls are highly sought after on the world market. The reason for this success is very much the focus on fertility. For example, for Holstein the weighting given to fertility in the Danish Total Merit Index, the S-index, was 0.18 in 1989, later increased to 0.26. When NTM was introduced in 2008, the weighting for fertility was increased to 0.41. This was subsequently 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 inseminations. This included collecting registrations and insemination of each bull planned for an insemination, together with accurate dating and recording of calving, registration of reproductive disorders, elimination of genetic defects etc.
On many dairy farms, visual inspection of cows in heat is supplemented with activity data measured by pedometers hung around the necks of cows and heifers. This kind of data enables more accurate detection of cows in heat and subsequently fewer inseminations to achieve pregnancy. 

Activity data have not yet been included in breeding value estimates, but research has shown that this is possible. Moreover, activity data can provide information about strength of heat and insemination time. The latter is of interest because research has shown that the time windows for insemination with conventional and sexed semen are different to maximise the chance of conception. According to farmers who use activity data for heat detection, they have seen an increase in fertility results compared to not using activity data. The greatest challenge to the use of activity data in breeding value estimation seems to be access to data as transferring large volumes of activity data from measuring equipment to the respective databases in the Nordic countries is not that simple.
Improving daughter and male fertility

The last 40 years of breeding for improved fertility in the Nordic countries has purely focused on improving daughter fertility – achieving pregnancy with the fewest possible semen doses and as quickly as possible after calving. With the introduction of genomic selection in 2008, we have seen a clear difference in the age of the insemination bulls. 

A typical age for a proven bull before genomic selection was at least six years whereas some of the insemination bulls used today are less than one year of age.
Semen quality from very young bulls after maturity is known in general to have lower pregnancy rate than an old bull. Due to this reality, VikingGenetics are focusing more on the evaluation of semen quality from young bulls. Little research has been done within this aspect, mainly because data are not readily available. In addition to cow data, we will need data on the bulls themselves. This should be detailed enough to give us data on each individual jump and be able to trace each dose from jump to insemination. VikingGenetics have initiated “The Digital Bull” project to shed light on male fertility and find areas for improvement. 

In conclusion, it is clear that VikingGenetics not only offer good opportunities for excellent fertility at Nordic dairy farms, but also for dairy farmers abroad who choose to use VikingGenetics products in their herd. The shift in focus to also include male fertility means that VikingGenetics remain an important company when it comes to achieving excellent fertility results around the world. 

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