Milk, caseinate and lactoferrin addition to equine semen cooling extenders

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 degrees C after resuspension with C1) milk- and glucose-based, C2) 0.6% caseinate, C3) C2+Lf 200gml(-1), C4) C2+Lf 500gml(-1) and C5) C2+Lf 1000gml(-1) extenders, and kept at 5 degrees C for 24h. 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 +/- 78.9m per x10(6) spermatozoa) compared with the fresh semen (8.6 +/- 1.9m per x10(6) spermatozoa). In contrast, the H2O2 concentrations were lower in the 0.6% caseinate extender (265.9 +/- 221.3m per x10(6) spermatozoa) than in the milk extender (430.9 +/- 199.8m per x10(6) 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 +/- 151.3m per x10(6) spermatozoa). Caseinate showed to be as efficient as milk to protect equine-cooled spermatozoon.