Eight breeding companies contributed foundation stock for a joint experiment on lean growth at the Animal Breeding Research Organisation (ABRO) and Wye College. All animals were test-mated to halothane positive (HP) reactors and incidences of HP reaction among progeny were used to estimate the frequency of the halothane gene (n) in the original herds. Estimated incidences of HP were compared with those observed in an earlier 1979 survey.

260 British Landrace (LR) were test-mated to HP (expected nn) LR at Wye, and 186 Large White (LW), including 18 boars standing at national AI centres, were test-mated to HP LR, Pietrain-Hampshire or LR x (LW x Norwegian Landrace) at ABRO.

Offspring were given a 4-minute halothane test at an average age of 50 days in LW and 76 days in LR. Numbers tested and incidences of reaction are shown in Table 1. Herds are coded ‘A’ to ‘I’ for anonymity. Purebred LR in herds A, C, D, E, H and I were halothane testec in advance and only halothane negatives (HN) were supplied for test-mating.