Ram semen frozen in pellets or straws has been shown to have comparable motility, morphology and fertility in research conducted by Westbreed and The University of Sydney, New South Wales and presented at the recent 11th International Ruminant Reproduction Symposium in Galway, Ireland.
Westbreed's Harry Wilson said the fertility of ram semen frozen in pellets versus straws had been a discussion for at least the past 35 years when Elders Genetics Services began marketing straws from Collinsville Merino stud in South Australia in the late 1980s.
"The arguments in favour of straws were mainly the ability to individually identify each single dose of semen, provide a uniform dose volume for each insemination and eliminate possible storage contamination through bio-secure packaging," Mr Wilson said.
"On the other hand, pellets require minimal capital investment in equipment, minimal consumables and a more simplified freezing process - resulting in significantly less production costs."
In 2021, semen was collected from four rams bred at three different Merino studs.
About 30 ejaculates were collected, split, and processed in either pellets or straws using techniques in common use across the artificial breeding industry.
A sample of pellets and straws from every ejaculate was analysed by The University of Sydney to determine numbers of sperm, morphology, post-thaw motility and incubation criteria.
Only those ejaculates where both the pellets and straws exceeded the minimum quality standards for frozen semen commonly accepted by the artificial breeding industry, were selected for insemination.
In November 2021, 536 ewes were inseminated in groups of about 70 head over six days within a two-week period.
Each group of 70 ewes was inseminated with either pellet or straw frozen semen from the same ejaculate on an approximate 50:50 ratio.
At 50 days post insemination, ewes were pregnancy tested and the number of foetuses from AI recorded.
Mr Wilson said results showed no statistically significant difference between pellet and straw frozen semen in post thaw motility incubation, sperm morphology or in vivo fertility.
"There is no difference in the fertility of ram semen frozen in pellets or straws when inseminated via laparoscopic AI," Mr Wilson said.
"Breeders can be confident that ram semen frozen in pellets or straws is of equal fertilising capacity."
Special thanks to the Button family, Manunda stud, Tammin, for the provision of animals in this project.
