rut 2 
(rŭt)
(rŭt)n.
1. A regularly recurring condition of fertility during which breeding occurs in certain mammals, especially deer and various other ungulates: a buck in rut.
2. The period during which this condition occurs.
intr.v. rut·ted, rut·ting, ruts
To be in rut.
[Middle English rutte, from Old French rut, from Vulgar Latin *rūgitus, from *rūgere, to roar, from Latin rūgīre, to roar.]