Interrogating the seminal fluid proteome to resolve the molecular basis of fertility in poultry

With more than 50 billion chickens reared every year for both eggs (layers) and meat (broilers), poultry is one of the largest and fastest growing food systems worldwide. Poultry already outcompetes other meat markets and by 2025 more than half of all the meat produced globally is forecasted to be chicken. In the UK, growth in the poultry sector has soared in recent years, with an estimated contribution of £3.3bn to UK GDP in 2014.

According to Defra, the UK poultry meat production increased to 1.8 million tonnes in 2017, with broilers accounting for around 85%. Currently, the UK is about 75% self-sufficient in poultry meat, and poultry meat represents the only UK livestock sector capable of quickly scaling-up production to support increased self-sufficiency of the UK. Ensuring consistently high fertility rates is key for meeting the demands of this expanding market.

Fertility in these flocks is notoriously variable and tends to decline as birds get older, through reproductive ageing. Poor male fertilising efficiency requires increased female exposure to males, which has additional repercussions because males are often aggressive to females, which reduces female condition, health and overall fecundity. Even small improvements in the fertility of breeding stocks have vast financial consequences; e.g. a 1% variation in fertility in broiler flocks was estimated to be worth hundreds of millions of US$ in the US market.

It is becoming increasing clear that in several organisms, the proteins contained in the male seminal fluid can have a drastic influence on fertility by modulating sperm swimming velocity, sperm storage within the female reproductive tract, probability of fertilisation and female behaviour after mating including female receptivity to further matings. The advent of proteomics and the publication of a draft genome of the chicken present a unique opportunity to investigate the role of seminal fluid proteins in poultry fertility.

Our recent work has characterised the seminal fluid proteome of natural ejaculates of a population of red junglefowl (the species that has given rise to the domestic chicken) and has shown that the seminal fluid proteome of these birds is complex with more than 1500 seminal fluid proteins (SFPs) identified so far, including proteins involved in various known biological functions e.g. immune responses and antibacterial defences, as well as sperm maturation and sperm motility. Our work has shown that some of these SFPs are associated with in vitro measures of sperm quality.

Importantly, our work has further shown that the seminal fluid proteome undergoes rapid and marked compositional changes in response to socio-sexual factors such as the sexual familiarity of a female partner and the social dominance of a male, and longer term changes, as males age, with males that are able to retain high sperm quality in advanced age having a distinct seminal fluid proteome. In this project, we capitalise on this wealth of preliminary knowledge to develop a research programme, to identify seminal fluid proteins (SFPs) that are important in maintaining lifelong fertility in male poultry.

We use the red junglefowl as benchmark experimental system that has not been influenced by domestication and artificial selection, to characterise proteomic repertoires associated with rapid responses to socio-sexual conditions (objective 1) and reproductive ageing (obj. 2), and identify SFP signatures causally linked to fertility. We then confirm the role of seminal fluid in driving variation in fertility (obj. 3), and validate the commercial relevance and applicability of these findings by investigating patterns of intra- and inter-male variation in fertility-linked SFPs in commercial meat-production domestic chicken lines (broiler breeders, obj. 4).

Collectively, these results will help us identify proteins linked to poultry fertility, which will inform new strategies to improve fertility in commercial stocks.