The role of Haemophilus somnus in early embryonic death. I. The effect of the organism on embryos by day 8 postbreeding.

A study using 23 healthy, mature, virgin Holstein-Friesian heifers was designed to determine if H. somnus caused detrimental effects in early bovine embryos and the mechanism(s) that induced these effects. Superovulated heifers were artificially inseminated 12 and 24 h after standing estrus using highquality, Haemophilus-free semen from a single ejaculate of one bull. Treatment heifers (n=12) were exposed by intrauterine infusion 12 h after the second insemination to approximately 1.5 x 10(9)H. somnus organisms (Iowa strain 1229) suspended in 10 ml of sterile 0.85% phosphate buffered saline (PBS). Control heifers (n=11) were inseminated and the infused with sterile PBS. Embryos were recovered 8 d after the second insemination using non-surgical technique and evaluated microscopically and graded on their estimated survivability. Representative embryos were also examined for in vitro culture survival time, histopathological changes, vital stain uptake and bacterial contamination. Following embryo recovery, uterine flush solution was centrifuged at 10,000 x G. Sediment was submitted for bacteriologic examination and supernatant preserved for quantitation of H. somnus immunoglobulins. Results to date indicate that H. somnus had a detrimental effect on early bovine embryos. H. somnus was recovered from the tissues of one treated animal. Significantly more (P </= 0.005) degenerated embryos were recovered from H. somnus -infected heifers than from control heifers. Embryos from H. somnus -infected heifers survived in culture media for a significantly (P </= 0.005) shorter time than embryos from control heifers.