In the Netherlands, the total number of sperm in a pig AI dose has decreased from 4.0 billion (1985) to 1.5 billion (started in 2008), resulting in a better use of the genetic potential of AI boars. Decreasing the number of sperm is only possible when the exact relationship between dose and fertility is known. Topigs Norsvin ran an analysis on the effect of number of sperm in the AI dose on fertility from 2007 to 2013, involving 584,787 fertility records from 6,241 boars. There was no effect of AI dose on farrowing rate (FR) (P=0.2366) nor on total number of piglets born (TNB) (P=0.1314) [1].
Next to using low doses of sperm, storage time also has a large impact on efficient use of boar semen. Until 2019, semen in the Netherlands was predominantly used in the first 3 days after collection (cut-off value of 70% motility for fresh semen, 60% motility after 3 days of storage). Detailed studies have been performed to prolong the useable length of storage. An in vitro semen quality trial was conducted with extenders from 4 different suppliers with semen stored up to 10 days. A study with 8 different extender variations (commercial and custom made), split sample testing one boar ejaculate from 29 boars with fair semen motility performance, revealed that some extenders outperformed the others over 10 days of storage (measured by motility and morphology). After a linear decrease, at day 5 the difference in motility and progressive motility between the highest and lowest performing extender was respectively 22% and 20%. Four hundred gilts were inseminated with semen stored up to 7 days and slaughtered at 35 days of pregnancy. There was no significant difference between extenders in pregnancy rate and embryo development. The best performing extender, SOLUSEM Bio+, was used to preserve semen at a further 12 commercial farms, with storage times up to 7 days. After a trial period of 11 weeks (6,543 animals inseminated with semen from 156 boars), no effect of storage time (0-3 days, 3605 animals inseminated, or 4-7 days 2938 animals inseminated) was found on FR (P=0.1548) and TNB (P=0.2684). Therefore, this new extender was used in daily routine AI semen processing at 1.3 billion cells per dose with extended storage guarantees (cut-off value of 70% for fresh semen and 65% and 60% motility for semen after respectively 3 and 5 days of storage). The results show that boars of high genetic merit can be used in the most efficient way, with semen stored for up to 7 days, in a geographically large area within and outside the Netherlands.