DELAYED INSEMINATION IS SUCCESSFUL WITH A NEW EXTENDER FOR STORING FRESH EQUINE SEMEN AT 15-DEGREES-C UNDER AEROBIC CONDITIONS

Milk-based semen diluents are known to be practical and effective in p rotecting equine spermatozoa during storage before artificial insemina tion. Milk is a biological fluid with a complex composition and contai ns components which are beneficial or harmful to spermatozoa. The aim of this study was to test the fertility of stallion semen after long-t erm storage using different milk diluents (INRA 82 or Kenney's diluent ) vs one diluent chemically defined (INRA 96), which is composed of ef ficient milk components and optimized for sperm survival and storage t emperature. The milk fraction used was that which best maintained sper matozoal survival based on motility measured in previous studies. Four breeding trials were conducted to determine the influence of combinat ion of new diluent and storage conditions on fertility of the stallion . We compared the standard protocol of storing semen in a skim milk di luent (INRA 82 or Kenney's diluent) at 4 degrees C under anaerobic con ditions with the experimental protocol which consisted of storing in a chemically defined, milk-free diluent (INRA 96), at 15 degrees C, und er aerobic conditions. After 4 breeding trials, in which the semen was stored for 24 h under the 2 protocols, we obtained 57% (n=178) and 40 % (n=173) of fertility per cycle using the experimental and the standa rd protocol respectively (p<0.001). Another breeding trial was conduct ed to determine the influence of storage time on the fertility of sper matozoa. We have compared the fertility of semen inseminated immediate ly (68% of fertility per cycle, n=50) vs the fertility of semen stored under the experimental protocol for 72 h before insemination (48% of fertility per cycle, n=52). The experimental protocol improved sperm f ertility compared to the standard protocol and seems to be a particula r alternative for stallions with cold shock sensitive spermatozoa. Sto ring semen for 72 h under the experimental protocol seems to be useful in the field. (C) 1998 by Elsevier Science Inc.