Mass motility assesses the three-dimensional collective movement of a group of spermatozoa. While it is well established that motility (regulated by the energy generated by metabolism) rapidly declines post-collection, the metabolic indicators associated with this decline in ram semen have not been described. Therefore, the aim of this study was to describe how ram sperm metabolism alters the pH and sugar content of the seminal environment. We hypothesised that pH would decline as acidic metabolic by-products are produced and the concentration of simple sugars would be exhausted as a result of glycolytic metabolism.
Ejaculates (n = 9) were collected from Merino rams via artificial vagina and incubated at 30°C. Mass motility, assessed on a scale from 0 (no motion) to 5 (numerous rapid waves) and the pH of undiluted ejaculates was recorded every 2 minutes until motility ceased. The sugar concentration (fructose and glucose) of ejaculates was assessed (D-Fructose/D-Glucose Assay Kit; Megazyme, Ireland) immediately post collection and once motility stopped.
Immediately post ejaculation, semen exhibited a mass motility of 5.0±0.00, pH 6.9±0.08 and sugar content of 7.9±0.80 g/L. After 34±3.5 minutes, the mass motility of semen reached 0.0±0.00 and pH and sugar content decreased to 5.7±0.09 and 5.3±1.28 g/L, respectively. This suggest that the motility of undiluted ram semen does not cease because of a lack of available substrates for glycolytic metabolism. Although motility and pH were correlated (r= 0.63, p= < 0.001), previous studies have found that mammalian sperm can retain motility within a pH range of 5.0 to 8.5 [1]. It therefore remains unclear if pH decline is the cause of the reduction in mass motility or if these are two separate events occurring simultaneously. The next stage of this work is to explore this link further, as well as the influence of seminal plasma on sperm metabolism.