201 EFFECTS OF REMOVING SEMINAL PLASMA DURING 8-h STORAGE BEFORE SEX-SORTING BOVINE SPERM

We evaluated sex-sorting parameters and post-thaw motility for sperm stored with or without seminal plasma for 8 h before sorting. One first ejaculate was collected from each of 6 bulls routinely collected via artificial vagina; ejaculates contained at least 70% motile and 75% morphologically normal sperm and sperm concentrations ranged from 0.75 to 2.21 × 109 sperm mL–1. Ejaculates were divided into 2 samples and centrifuged at 1000 × g for 15 min. Seminal plasma from 1 sample was replaced with TALP (pH 7.4) to a sperm concentration of 1.4 × 109 sperm mL–1. The seminal plasma/sperm admixture of the other sample (control) was suspended to initial ejaculate sperm concentration. Both samples were stored for 8 h at 16°C before being subjected to standard sex-sorting procedures. Sperm were analyzed and bulk sorted on a MoFlo SX (XY Inc., Navasota, TX, USA) flow cytometer/cell sorter for percentage of live-oriented cells, percentage of membrane-impaired sperm (cell membranes permeable to red food colouring, which were discarded during sorting) and resolution between X- and Y-bearing sperm populations (peak to valley ratio). Sorted sperm were frozen according to standard procedures and post-thaw motility was determined immediately after thawing using computer-assisted sperm analysis. Treatments were compared using a paired t-test. Control sperm stored with seminal plasma resulted in a higher percentage of live-oriented cells (55%) versus those stored without seminal plasma (51%; P = 0.02). The percentage of membrane-impaired sperm was lower for control sperm (19%) than that of samples without seminal plasma (28%; P < 0.001). Resolution was greater for sperm stored without seminal plasma (34%) than for control sperm (10%; P = 0.04). Post-thaw, both total and progressively motile sperm were higher for samples without seminal plasma (63 and 53%, respectively) compared with those of the control samples (52 and 45%, respectively; P < 0.04). In conclusion, sperm stored for 8 h without seminal plasma had greater resolution between X- and Y-bearing populations and higher post-thaw motility than control sperm. However, these samples had a higher percentage of membrane-impaired sperm that were removed during sorting. Long-term storage of sperm in their seminal plasma before sex-sorting appears to be detrimental to post-sorting, post-thaw sperm motility.