Fertility of ram semen after storage at 5°C

Abstract

In five experiments, fertilization, early (18–19-day) pregnancy, and lambing were examined after insemination with semen stored at 5°C in tris-fructose-egg yolk diluent. After deposition into uterine horns by surgical insemination of semen stored for 0 (control), 2, 4, 6, 8, 9 or 10 days, fertilized eggs were recovered in 32 34 , 16 16 , 21 22 , 15 20 , 9 17 , 2 18 and 1 15 ewes; the 18–19-day pregnancy rates determined by progesterone assay were 32 48 , 15 28 , 11 20 , 12 20 , 9 20 , 2 20 and 1 21 for the respective storage periods. There was a linear decrease in fertilization rates beyond 4 days of storage and in early pregnancy rates after 6 days of storage ( P<0.001). The decline with time of storage in the fertilization rate was not associated with an increase in early embryonic loss. Surgical insemination with semen stored for 0, 4, 6, 8, 9 and 10 days resulted in 53, 35, 40, 25, 5, and 0% lambing. Single cervical (normal) insemination of a total of 281 ewes with 0, 1, 2 or 3-day-old semen, using within each semen treatment 90 × 10 6 and 180 × 10 6 spermatozoa, yielded mean lambing rates of 60.0, 34.3, 33.8, and 17.1%; and after using 150 × 10 6 and 300 × 10 6 spermatozoa in a total of 393 ewes the mean lambing rates for the above semen treatments were 69.0, 46.4, 36.1, and 24.2% (linear, P < 0.001). In both tests the lambing results were better after insemination of the higher number of spermatozoa, but the slope of decline in fertility with age of semen was not affected by the sperm dose. When single and double cervical inseminations were performed in a total of 411 ewes, with 150 × 10 6 and 300 × 10 6 spermatozoa per inseminate, the lambing rates for semen stored for 0, 1, 2 and 3 days were 57.7, 30.4, 26.8, and 4.7% after single insemination, and 66.7, 56.8, 46.4, and 41.5% after double inseminations. The sperm dose within method of insemination and semen treatment had no effect. The lambing rate was better after double than single insemination ( P<0.001), but the slope of decline in fertility with age of semen was not significantly affected by number of inseminations. In the final experiment, involving 408 ewes, 300 μg of prostaglandin F 2α added to the inseminate did not improve the fertility of fresh semen or semen stored for 1 day.