Hur påverkar inavel fruktsamheten hos häst?

Sammanfattning: Inbreeding has become a problem in some horse breeds. Studies show that it may lead to inbreeding depression which affects e.g. reproduction traits. In the wild there are mechanisms that make horses avoid mating with close relatives. When selection is done by humans this mechanism is removed and intensive breeding for a few traits, for example good racing results, can become a problem. A small population may have more difficulties to maintain a large genetic diversity, for example the Friesian horse and the Hucul horse. The Friesian population has decreased substantially in number over the past hundred years and the population of the Hucul horse is small and closed. This has resulted in an increased rate of retained placenta in Friesian mares and a decrease in fertility and fecundity of the Hucul horse. Larger populations may be affected by inbreeding as well. Inbreeding in the Thoroughbred horse has increased during the past ten years, which may explain a shorter and more intense racing season. It is more profitable to have a high turnover of horses instead of focusing on sustainable breeding individuals. Studies of the Norwegian trotter have shown that inbreeding has an effect on early abortions. Studies of Standardbred trotters and Finnhorses in Finland show that a higher inbreeding coefficient is significantly correlated with a lower foaling rate. A high inbreeding coefficient results in a reduced semen quality in Shetland pony stallions. A major challenge today is to get a high genetic gain in breeding and still avoid inbreeding caused by too few selected breeding animals.