Predicting sire fertility in artificial insemination of dairy cows by the ability of spermatozoa to bind to oviduct cell aggregates.

Abstract

This study aimed to evaluate sperm morphofunctional characteristics and the ability of spermatozoa to bind to oviduct epithelial cell (OEC) aggregates as predictors of male field fertility. Based on pregnancy per artificial insemination (P/AI) data of 1,833 services in Holstein cows from a commercial dairy herd, sires were classified as of higher (HF, P/AI = 35.0% [362/1,034], n = 3) or lower (LF, P/AI = 21.4% [171/799], n = 4) fertility. Semen quality was assessed based on sperm motility (by computer-assisted sperm analysis, plasma and acrosome membrane integrity, mitochondrial membrane potential, membrane lipid peroxidation, and membrane fluidity [by flow cytometry], and OEC binding). For the analysis of OEC binding, the oviduct isthmus region from abattoir tracts was dissected, and cells were incubated for 24 h to allow OEC aggregate formation, followed by co-incubation with 1 × 10⁵ motile sperm. Bound sperm were counted at 4 time points: 0.5, 12, 24, and 36 h. Statistical analyses were conducted using the GLIMMIX procedure in SAS 9.4 (SAS Institute Inc.). Sperm motility characteristics were not different between HF and LF sires, except for greater straight-line velocity in HF (HF: 94.7 ± 3.1 μm/s vs. LF: 80.9 ± 3.1 μm/s). Flow cytometry analysis was not able to explain the difference between fertility groups (P/AI). However, in the sperm binding test to OEC, the HF sires tended to have more bound sperm per millimeter of OEC than LF sires at 0.5 h of co-incubation (59.1 vs. 54.0). At h 12 (36.5 vs. 28.6), 24 (24.0 vs. 15.3), and 36 (26.0 vs. 12.1), HF sires had more bound sperm per millimeter of OEC than LF sires. Field fertility was positively correlated (r = 0.89) with the number of sperm bound per millimeter of OEC at 36 h of co-incubation. These results suggest that LF sires may have impaired fertility due to a reduced ability to bind to oviduct cells in vivo. In addition, the result showed the potential of sperm binding test to OEC for early evaluation or prediction of bulls' fertility, although more studies are being performed to refine the procedures during these assays, as well as to better understand other potential physiological mechanisms differing between HF and LF sires.