OLFACTORY AND VOMERONASAL CHEMORECEPTION AND THE DISCRIMINATION OF ESTROUS AND NON-ESTROUS EWE URINE ODORS BY THE RAM

Four sexually experienced adult rams were trained using operant conditioning techniques to discriminate between fresh oestrous (Day 1 of the oestrous cycle) and fresh non-oestrous (Days 7-11) ewe urine odours. Two selective sensory deprivation techniques were used to localise the chemoreceptors mediating the discrimination: (1) vinyl polysiloxane bungs to occlude the nasopalatine canals (NPC) and block stimulus access to the vomeronasal organs (VNO); (2) irrigation of the nasal cavities with zinc sulphate solution to induce reversible olfactory deficits. Ram's abilities to flehmen and detect aversive odours following each treatment were also recorded. Both normal and NPC-occuluded rams could discriminate between oestrous and non-oestrous urine odours, perform flehmen and detect aversive odours. One of the 2 rams treated with zinc sulphate had olfactory deficits in all tests and did not flehmen. A second ram treated with zinc sulphate initially showed similar deficits, but retained the ability to detect aversive odours. The deficits in the second ram were temporary. These results demonstrate that odour access to the VNO is not necessary for adult rams to discriminate between oestrous and non-oestrous ewe urine odours. The chemoreceptors mediating this discrimination are located intranasally, probably in the main olfactory epithelium. Zinc sulphate solution, applied intranasally, may selectively destroy intranasal chemoreceptive fields and maintain some olfactory function, such as the detection of strongly aversive odours. © 1990.