The effect of dietary Alginate Oligosaccharides on boar semen quality

China is not only the largest pork producer in the world, but also the largest pork consumer. In China, the annual production of pork exceeds 50 million tons, accounting for more than 40% of the worldwide production. Nevertheless, compared with European countries such as The Netherlands and Denmark, the swine raising technology of China is still falling behind. There are many reasons for this delay in production, of which boar semen quality is a particularly critical one. The reproductive capacity of boars not only directly determines the economic benefits, but also affects the reproductive performance of sows in large-scale pig farms. The raw semen of boars should meet the standards of artificial insemination, so that a normal conception rate of sows can be guaranteed. Therefore, it is very important to improve boar semen quality to further ameliorate reproductive performance in swine.
Maintaining the sexual desire of a boar, and increasing its sperm volume, sperm concentration and sperm motility are important objectives for animal husbandry workers in large scale boar studs. There are many factors that affect boar semen quality, such as breeding management, disease status, nutritional level, environment, and age. On the one hand, in the south of China, the summer climate is represented by high temperatures and high humidity levels, especially between June and September, and the boar semen quality and utilization rate decrease significantly in that period. On the other hand, as the age of a boar increases, the semen quality will gradually decrease as well, which results in an increased elimination rate of boars in large-scale boar studs. With the ban on antibiotics, more and more research has been shifted towards natural plant extracts. Alginate oligosaccharide, as a natural plant extract, has multiple biological functions such as immune regulation, and it has antioxidant, anti-inflammatory and even anti-cancer properties. However, the regulation mechanism of AOS on the semen quality of boars is not clear.
In a first experiment in this PhD, it was demonstrated that AOS supplementation improved sperm motility significantly (P<0.05). Advantageous blood and sperm metabolites changed. Meanwhile, the gut microbiota diversity changed at both phylum and genus level, and the relative abundance of beneficial microbes improved, while the relative abundance of harmful bacteria reduced. Therefore, AOS improved semen quality by affecting gut microbiota and metabolites in blood and sperm.
In a second experiment in this PhD, everyday temperature and humidity were recorded during the experimental period. The Temperature-Humidity index (THI) was also calculated to proof the boars were in the heat stress condition. AOS significantly improved sperm motility (P<0.001) and sperm concentration (P<0.05). AOS supplementation also improved the sperm metabolites, changed the composition of gut microbiota, changed the relative abundance of beneficial bacteria, reduced the relative abundance of harmful bacteria, and improved the amount of short chain fatty acids. Proteomic results showed that AOS improved proteins related to spermatogenesis, while decreasing heat shock protein 70 (P<0.05) and heat shock protein 90 (P<0.01). Therefore, AOS can be used as a feed additive to improve semen quality of boars to enhance reproductive performance under heat stress.

A third experiment focused on AOS in an extended service lifespan context. The results showed that in older boars AOS supplementation significantly improved sperm motility (P<0.05) and sperm validity rate (P<0.001), and significantly reduced the abnormal sperm rate (P<0.01) as well. At the same time, AOS significantly improved the testosterone levels in the blood (P<0.01) induced the presence of beneficial metabolites such as adrenic acid (P<0.05) and succinic acid (P<0.05), and significantly reduced harmful substances such as dibutyl phthalate (P<0.05). AOS supplementation changed the composition of gut microbiota, altered the relative abundance of beneficial bacteria, and reduced the relative abundance of harmful bacteria, as well as rise the level of short chain fatty acids, similar as was observed in the other two experiment on younger boars. Therefore, AOS boosted semen quality of aging boars by improving the intestinal microbiota and sperm metabolome. AOS can thus be used as a feed additive to solve the problem of high elimination rate in large scale boar studs.
In summary, this PhD thesis focused on the boar sperm metabolome, sperm proteins and gut microbiota in improving sperm parameters such as sperm motility, sperm concentration, and abnormal sperm rate. The PhD explores the effects of AOS on boar semen quality in different conditions (under heat stress and in aging boars), and provides a theoretical basis for AOS using in swine industry as feed additives.