Farmers philosophy key to fertility success All about a dairy farm begins with a calf, and a satisfying 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 related to 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 favourable 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 realise that it is expensive to raise heifer calves both for their own use and for 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 was created, breeding values for fertility have been calculated in the Nordic countries. In the 1980s and 90s, the target was very much about increasing milk production which meant import 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 such that more bulls were selected from pedigrees with an increased focus on fertility and at the same time avoiding some international pedigrees with poor fertilityrelated performance. The effect of this change was most evident in Holstein where a rapid increase in genetic level has been observed until this day. A similar trend can be observed in Jersey and the red breeds but at a lower level because these breeds, in general, have better fertility than Holstein. Figure 1 shows genetic trends for fertility in Holstein, based on the Interbull fertility index, and comparing 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. From a VikingGenetics point of view it is also important to know how our bulls compare with bulls from other countries. 4 INNOVATIVE BREEDING MAY 2020
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