13 MOTILITY CHARACTERISTICS OF SPERMATOZOA FROM BULLS GRAZING TALL FESCUE PASTURES

Abstract

Fertilisation is less than expected with spermatozoa from bulls consuming toxic endophyte-infected (E+) tall fescue. The objective of this study was to evaluate motility characteristics of spermatozoa from bulls grazing tall fescue pastures using computer-assisted sperm analysis (CASA). Semen was collected from six Angus bulls (average age = 15.1 ± 0.04 months) during a three-month grazing study. Bulls grazed Kentucky 31 tall fescue (Festuca arundinacea Schreb.) infected with Neotyphodium coenophialum, an ergot alkaloid-producing endophyte (n = 3), or Jesup tall fescue with Max-Q™ (NTE), a non-ergot alkaloid producing endophyte (n = 3), and grouped by body weight and scrotal circumference to graze pastures from April 18 to June 26. Semen was collected once per week between 0600–0800 h beginning in mid-May and ending the last week of June. Gross motility and morphology was evaluated before extending with Bioxcell® animal protein-free formula (IMV, Aigle, France) and antibiotics (CSS 100, 2% of total volume). Extended semen was then evaluated using CASA to determine final dilution and packaged into straws (20 million sperm/straw), where equilibration occurred over 3 h in a cold room at 4°C. Straws were frozen for 7 min in static vapor of liquid nitrogen and plunged into goblets filled with liquid nitrogen. Semen was thawed and assessed using CASA at 0 and 3 h post-thaw. Data were analysed as a randomised block design with the fixed effects of treatment, blocking on semen collection date, utilising the mixed models procedure of SAS 9.2 (SAS Institute Inc., Cary, NC, USA). Data were tested for normality (Shapiro-Wilk W ≥ 0.90), and treatment differences were determined using F-protected least significant differences. Path velocity (P = 0.001) and progressive velocity (P = 0.003) were lower in spermatozoa from bulls grazing E+ during the last 2 weeks of collection in June independent of time of assessment post-thaw. Sperm head area decreased in size in spermatozoa from E+ grazing bulls at 3 h post-thaw (P = 0.04) compared with NTE grazing bulls. Percent of rapid (progressive % with path velocity >50 μm s^–1) and medium (progressive % with path velocity <50 μm s^–1 but > 30μm s^–1) velocity spermatozoa was decreased for E+ grazing bulls compared to NTE grazing bulls (P < 0.0001 and P = 0.004, respectively) and was accompanied by an increase in static (immobile) spermatozoa from E+ bulls (P < 0.0001). These findings indicate that spermatozoa movement and velocity are impaired in bulls grazing E+ tall fescue pastures compared to bulls grazing NTE tall fescue pastures after the freeze and thaw process, which may explain decreased fertilisation and cleavage rates of oocytes co-incubated with these spermatozoa.