Temperatures from 4 to 15 °C are suitable for preserving the fertilizing capacity of stallion semen stored for 22 h more in INRA96 extender

This study tested whether variable temperatures (from -0.5 to 15 degrees C) and air exposure could be used under laboratory and under field conditions to store stallion sperm diluted in extender INRA96 without loss of fertility. Experiment 1 (laboratory conditions) measured the effects of two 72 h storage conditions (5 degrees C with air vs. 15 degrees C without air). Experiment 2 (fixed field conditions) measured the effects of 22 h of storage without air in disposable containers maintained at four ambient temperatures (7 degrees C, 17 degrees C, 27 degrees C, 39 degrees C with semen at -0.5 degrees C to 3 degrees C, 4 degrees C to 7 degrees C, 8 degrees C to 10 degrees C, 12 degrees C to 15 degrees C, respectively). Per cycle pregnancy rate (PC) was measured after one artificial insemination (AI) in uterine body of 200 X 10(6) total spermatozoa, 7 h (Experiment 1) or 17 h (Experiment 2) before ovulation. In Experiment 1, PC was similar for both conditions (60% (n = 40 cycles) vs. 63% (n = 40), respectively, 5 stallions X 8 cycles). Only velocity VCL and ALH were slightly higher at 15 degrees C. In Experiment 2, PC was reduced when ambient temperature was low (semen at -0.5 degrees C to 3 degrees C; PC = 25%) rather than intermediate (semen at 4 degrees C to 7 degrees C; PC = 53%) or high (semen at 8 degrees C to 10 degrees C; PC = 50%) (4 stallions X 8 cycles) (P = 0.002). Sperm stored at -0.5 degrees C to 3 degrees C had lower acrosome integrity/responsiveness, similar membrane integrity (HOS test) and motilities, and higher VCL and ALH, than semen stored between 4 and 15 degrees C. These results demonstrate a wide tolerance of equine sperm to variable positive temperatures and air exposure for 22 h storage and more. However, temperatures close to 0 degrees C are detrimental for fertility