Low temperature preservation: Influence of putative bioactive microalgae and hop extracts on sperm quality and bacterial load in porcine semen

Abstract

The frequent use of antibiotics in artificial insemination promotes the development of antibiotic resistance. Therefore, alternatives must be considered. In this study, putative bioactive microalgae and hop extracts were examined to estimate their effect on quality and bacterial load of preserved porcine semen when used a low-temperature storage at 5 °C in Androstar® Premium (ASP) extender (Minitüb). Firstly, five algae extracts (Neochloris oleoabundans (NEO), Pseudococcomyxa simplex (PSEY), Phormidium ambiquum (PHA), Schizochlamydella minutissima (SCH), Cyanidioschyzon merolae (CYA)) and one hop extract (Humulus lupulus (HOP)) in four concentrations (0.2, 2, 20 and 200 μg/mL) were tested on their sperm-compatibility at 17 °C. All extracts in the concentrations 0.2 and 2 μg/mL appeared to be sperm compatible. After 72 h of storage at 5 °C, variants showed an increase of total bacterial subcultures from 103 (ASP w/o supplements) to 113/136/135/136/126/118 (ASP w/NEO/PSEY/PHA/HOP/SCH/CYA). Even though bacterial growth was not inhibited in general, all extracts showed an antimicrobial effect on specific bacteria, including Gram-positive (Trueperella pyogenes, Streptococcus porcinus) and Gram-negative bacterial species (Alcaligenes faecalis, Pseudomonas aeruginosa, Ralstonia sp., Pasteurella sp., Proteus sp., Providencia stuartii, and Escherichia coli). While the proportion of these species was 10% in the control (ASP w/o supplements), their proportion in the supplemented variants ranged from 8% (NEO, HOP) to as low as 3% (PSEY). Although the tested extracts are not suitable to replace conventional antibiotics due to their lack of broad-spectrum antimicrobial activity, they nevertheless present promising opportunities for bacteria-specific, customizable usage in boar semen extenders combined with antibiotics or other antimicrobial agents.