Possible Clues:

• Who in France tucks into wild oxen as a regular event?
• Annual moments when day and night both last about 12 hours everywhere
• When the sun is directly above the equator
• Horse briefly ahead of bovine for a day in September, say?
• Time of year when zebra almost mounts zebu?
• March features one short horse with bullock following?
• Biannual occurrence in which bovine follows side of slope that's one in five
• March or September date
• In astronomy, a point on the celestial sphere at which the ecliptic intersects the celestial equator
• Vernal/autumnal --