The frequency of Calf Recumbency has increased significantly since 2010: its increased from less than 5% up to 11% of the total amount of the genotypized female Holstein pupulation.
The test for this genetic condition is now available and, from the first results, some A.I. bulls have been identified as MW carriers. The origin of the mutation is attributed to Southwind Bell of Bar-Lee, a bull from 1984. Also Supersire is mentioned as one of the most important carrier in the last decade.
However, the expression of this genetic defect is characterized by incomplete penetrance, which means that not all carriers manifest the problem (a characteristic of numerous genetic diseases).