design: RNA was extracted from 36 samples (each containing the sperm of 20 males of one selection line) in six batches of six samples each, using a custom. 1l small RNA spike-ins (Exiqon) were added after lysis and before the extraction. RNA was extracted in 8l nuclease-free water. NGS libraries were prepared from 6l RNA using NEB small RNA library prep kit (E7330) protocol. All 36 samples were processed in a single batch, with an end library volume of 100l.