181 FERTILIZATION CHARACTERISTICS OF SPERMATOZOA FROM BULLS GRAZING TALL FESCUE PASTURES

Abstract

Fertilization with spermatozoa from bulls ingesting elevated concentrations of ergovaline [i.e. consumption of toxic endophyte-infected (E+) tall fescue] results in reduced cleavage rates. Thus, the objectives of the current study were to evaluate motility and penetration rates of spermatozoa from bulls grazing tall fescue pastures and intracellular calcium (Ca²⁺) parameters of presumptive zygotes (PZ). During a 3-month study, 6 Angus bulls (average age = 15.1 ± 0.04 months) were appointed to graze Kentucky 31 tall fescue (Festuca arundinacea Schreb.) infected with Neotyphodium coenophialum, an ergot alkaloid-producing endophyte (n = 3), or Jesup tall fescue infected with non-ergot alkaloid-producing endophyte (NTE) MaxQ™ (n = 3). Bulls were grouped by bodyweight (BW) and scrotal circumference (SC) to graze pastures from April 18 to June 26. Blood samples, BW, SC, semen and rectal temperatures (RT) were collected every 7 days. Semen was evaluated for gross motility, morphology and computer assisted semen analysis (CASA) parameters. Semen from a subset of bulls (n = 2 per treatment; acceptable motility after 3-h stress test) was used to assess spermatozoa function using in vitro assays; that is, in vitro production of embryos, penetration rates obtained 6.5 to 7.5 h post-insemination (hpi) and intracellular Ca²⁺ measured 8.0 to 10.0 hpi. Data were analyzed using a mixed models procedure (semen data), generalized linear mixed models (in vitro data) and nonlinear regression (intracellular Ca²⁺ data) of SAS 9.2 (SAS Institute Inc., Cary, NC, USA). Concentrations of serum prolactin were higher in bulls grazing NTE compared with those of the bulls grazing E+ tall fescue pastures (123.43 ± 9.23 ng mL^–1 vs 97.13 ± 9.23 ng mL^–1, respectively; P = 0.05). Gross motility of spermatozoa (90.95 ± 2.67% vs 85.62 ± 2.67%, NTE and E+ respectively; P = 0.17) and percent normal morphology (77.14 ± 1.93% vs 77.61 ± 1.93%, NTE and E+ respectively; P = 0.87) before cryopreservation did not differ. However, motility immediately post-thaw (58.27 ± 2.81% vs 43.84 ± 5.30%, NTE and E+, respectively; P = 0.02) and following a 3-h stress test (51.13 ± 3.88% vs 23.33 ± 3.23%, NTE and E+, respectively; P < 0.0001) were decreased for spermatozoa from bulls grazing E+ tall fescue. The percentage of PZ that cleaved was higher for oocytes fertilized with spermatozoa from bulls grazing NTE (76.30 ± 3.93%) compared with that of the bulls grazing E+ tall fescue pastures (58.92 ± 3.9%; P = 0.007; n = 1539 PZ, n = 10 replicates). Penetration rates were higher in oocytes fertilized with spermatozoa from NTE bulls (87.42 ± 1.63%) compared with that of E+ bulls (64.54 ± 3.28%; P < 0.0001; n = 2547 oocytes, n = 33 replicates). Meiotic progression of maternal chromatin was hastened in oocytes penetrated by spermatozoa from bulls grazing E+ compared to that from bulls grazing NTE tall fescue. Intracellular Ca²⁺ parameters (baseline, P = 0.01; amplitude, P = 0.0002; and area under the curve, P = 0.006) were reduced in PZ fertilized with spermatozoa from E+ bulls (n = 192 oocytes, n = 4 replicates). These findings indicate impaired spermatozoa function in bulls grazing E+ tall fescue pastures that extends beyond gross semen characteristics and may provide direction for future studies.