9 BIRTH OF CALVES AFTER ARTIFICIAL INSEMINATION WITH CRYOPRESERVED BOVINE EPIDIDYMAL SPERMATOZOA HARVESTED FROM POSTMORTEM BULLS

Abstract

Recently, interest in the preservation of epididymal sperm as a potential source of valuable genes for genome resource banks has increased. The ability to recover and cryopreserve postmortem epididymal sperm will allow the use of valuable gametes from a breeding male that dies unexpectedly. The objective of this study was to produce pregnancies and live births from AI by using frozen–thawed bovine caudal epididymal sperm. Paired testes were obtained from mature, mixed-breed beef bulls (n = 3) from a local abattoir and transported to the laboratory (within 5 h postmortem) in a Styrofoam box at a temperature that ranged between 28 and 29°C. The mean ± SEM weights of the pair of testes and caudae epididymides were 345 ± 9g and 10 ± 2g, respectively. Epididymal sperm from each bull were harvested by multiple incisions from the caudae epididymides, pooled, and then rinsed with 4 mL of egg yolk Tris-glucose citric acid monohydrate extender (EYT-GC). Harvested sperm samples were placed in a refrigerator at 4°C for 4 h before the addition of cryoprotectant. Samples were diluted slowly over a period of 30 min 1:1 in EYT-GC extender containing 14% glycerol to obtain a final concentration of 7% glycerol. Sperm concentration was adjusted to 35 million/straw and loaded into previously cooled 0.5-mL plastic straws. Straws were placed 2 cm above liquid nitrogen (LN₂) vapors for 10 min and then plunged into LN₂. Sperm were stored for 1 year before thawing. Luteal-phase crossbred beef cows were synchronized with a single 25-mg injection (i.m.) of prostaglandin, and those displaying standing estrus (n = 6) were each inseminated with 1 straw by a single technician from 1 bull 12 to 18 h after the onset of standing estrus. Straws were thawed for AI in a 37°C water bath for 40 s. Three of the 6 cows inseminated (50%) were diagnosed as pregnant by transrectal ultrasonography at 45 days post-AI. All 3 pregnant cows (100%) delivered healthy singleton calves (2 males and 1 female, with an average birth weight of 37 ± 2.5 kg), resulting in a mean gestation length of 286 ± 1.9 days (range: 282–288 days). We can conclude that epididymal sperm can be extracted by 5 h postmortem from bull testes, frozen, and subsequently used for the production of live offspring from AI. Further research is needed to improve this technology to optimize the utilization of valuable bovine male gametes.