In Iranian Holstein cattle [36], on chromosome 2, the ADP ribosylation factor-like GTPase 5A (ARL5A), calcium voltage-gated channel auxiliary subunit β 4 (CACNB4) gene associated with calving to first service was identified, which is the same gene that was associated in the present work with HF (Table S1). This evidence concerns the gene CACNB4 and hydrops fetalis.