FERTILITY OF BULL SEMEN PACKAGED IN .25- AND .5-MILLILITER FRENCH STRAWS

The fertility of bull semen packaged in .25- and .5-mL french straws w as compared. One ejaculate from each of five Holstein bulls was split, extended to 10 x 10(6) spermatozoa/inseminate dose in whole homogeniz ed milk, packaged in .25- and .5-mL french straws, fr ozen in liquid n itrogen (LN) vapor, and stored in LN. Semen was thawed at 37 degrees C for 30 s. Synchronized heifers (n = 1,360) were inseminated (during a 12-mo period) with semen packaged in either a .25- or .5-mL french st raw. Blood was collected on the day of insemination and the serum was assayed for progesterone. Heifers with blood progesterone levels of > 1 ng/mL were eliminated from the data. Blood was collected at 30 to 45 d after insemination and the serum was assayed for the presence of bo vine pregnancy-specific protein B (bPSPB) by RIA to determine pregnanc y. Conception was 63.6 and 62.0% (P = .55) for semen packaged in the . 25- and .5-mL french straws, respectively. There was neither a bull x packaging unit interaction CP = .49) nor a day of insemination x packa ging unit interaction (P = .87). Conception among bulls ranged from 57 .1 to 68.0% (P = .19). No evidence was found that meteorological facto rs influenced conception. Under the conditions of this experiment, sem en packaged in the .25- and .5-mL french straw had similar fertility.