Caseinate protects stallion sperm during semen cooling and freezing.

: Extenders with a defined composition containing only components with clearly protective effects on sperm during storage would be an advantage. The aims of the present work were to assess whether caseinate, improves cooled and frozen equine semen quality. Semen from six stallions were suspended with four different cooling extenders C1) Kenney extender; C2) 0.6 % caseinate; C3) 2.7 % caseinate ; and C4) C1 + 2.1 % caseinate, and frozen extenders: F1) INRA 82 extender; F2) 1.35 % caseinate; and F3) 2.7 % caseinate. Although there was no significant difference between the motility rate among the cooled (C1:45.0, C2:36.7, C3:38.3 and C4:48.3) and frozen extenders (F1:16.9, F2:21.1 and F3:18.6), significant higher values of sperm velocity variables were observed with the 1.35 % caseinate extender compared to the control (VSL: 40.8 x 18.9 and VAP: 46.8 x 25.0 µm/s), respectively. Caseinate seemed to be responsible for sperm protection during preservation and showed to be as efficient as milk.