Milk, caseinate and lactoferrin addition to equine semen cooling extenders.

Summary Cooled semen has been used routinely to prolong sperm viability until artificial insemination time. However, spermatozoa are subjected to oxidative stress. The aim of the present work was to investigate the protective and antioxidant effect of the milk proteins lactoferrin (Lf) and caseinate added to equine semen cooling extenders. Semen from six stallions was cooled at 5 °C after resuspension with C1) milk- and glucose-based, C2) 0.6% caseinate, C3) C2 + Lf 200 μg ml−1, C4) C2 + Lf 500 μg ml−1 and C5) C2 + Lf 1000 μg ml−1 extenders, and kept at 5 °C for 24 h. Sperm motility characteristics and intact membrane rates were not different among the treatments (P > 0.05). As a result of the cooling process, the nitrite concentration increased significantly in the cooled semen (69.6 ± 78.9 μm per ×106 spermatozoa) compared with the fresh semen (8.6 ± 1.9 μm per ×106 spermatozoa). In contrast, the H2O2 concentrations were lower in the 0.6% caseinate extender (265.9 ± 221.3 μm per ×106 spermatozoa) than in the milk extender (430.9 ± 199.8 μm per ×106 spermatozoa, P < 0.05), showing an antioxidative effect of the caseinate compared with the milk. However, in all groups, hydrogen peroxide concentrations were similar to the undiluted fresh semen (332.8 ± 151.3 μm per ×106 spermatozoa). Caseinate showed to be as efficient as milk to protect equine-cooled spermatozoon.