[Grey, curly and short-haired Swiss Holstein cattle show genetic traces of the Simmental breed].

INTRODUCTION Occasionally black-and-white spotted calves appear in Switzerland, which show a special fur only in the pigmented area. Otherwise these animals are normally developed. The white hairs are normal, but they appear relatively long and smooth, because the pigmented hairs are curly and thus appear shortened. In addition, the affected animals show a variable intensity of coat colour in the pigmented area. At birth affected calves often appear black, whereas older cattle show bright colours from reddish brown to grey. This is associated with a variable hair loss that increases during growth and is limited to the pigmented area of the coat. In adult cattle the coloured hairs appear rather smooth, but they are considerably shorter. This phenomenon of pigmentation-associated hypotrichosis was previously described internationally in various beef cattle populations. The affected cattle are often solid black and show only small white spots. Therefore, the loss of hair at the pigmented fur and most visibly at the pigmented tail is called rat-tail syndrome. Another name used is also crossbreeding-related congenital hypotrichosis. Molecular genetic investigations showed that the affected animals are heterozygous carriers for two variants in two different genes associated with pigmentation. The same genotype constellation was found in the 33 similarly affected cattle from Switzerland presented here. On one hand, they each carry a copy of the MC1R gene gain-of-function variant causing dominant black, as well as a copy of the recessively inherited red factor loss-of-function variant in the MC1R gene. On the other hand, all cases are heterozygous carriers for a variant in the PMEL gene that is associated with a semi-dominantly inherited form of colour dilution (dun or silver) in Simmental, Hereford and Highland Cattle. The introgression of Holstein cattle into the Original Simmental breed, which has been practised for decades, explains the occasional occurrence of this phenomenon in Swiss cattle breeding.