Morphology, membrane integrity, and mitochondrial function in sperm of crossbred beef bulls selected for residual feed intake

The objectives of this study were to compare morphology, plasma and acrosome membrane integrities, and mitochondrial function in sperm of bulls selected for low- vs. high-residual feed intake (RFI). Semen samples obtained from 10 low- and 8 high-RFI yearling crossbred beef bulls were evaluated. Assessment of sperm morphology was performed by microscopy, and sperm membrane integrity and mitochondrial membrane potential (MMP) were evaluated by flow cytometry. Parameters of sperm morphology evaluated did not differ between low- and high-RFI bulls. Compared with high-RFI bulls, low-RFI bulls had an increased proportion (least square mean ± standard error) of sperm with actively respiring mitochondria (54.2% ± 2.9% vs. 43.6% ± 3.3%, P = 0.03). However, a greater proportion of sperm from low-RFI bulls had low MMP (34.4% ± 4.2% vs. 19.0% ± 4.7%, P = 0.03). Results indicate that selection for improved feed efficiency does not compromise bull sperm morphology and viability. However, despite greater mitochondrial activity, the increased proportion of mitochondria with low membrane potential in sperm of low-RFI bulls warrants further investigation to rule out any potential negative effects on fertility.