The effects of selection for lean growth and the halothane allele on growth performance and mortality of pigs in a tropical environment

Abstract

The effects of the halothane allele and other genes for rapid lean growth were examined in pigs grown in an environment of high temperature/transport stress. The halothane allele n was segregating with its normal alternative N in a line which had been selected for rapid lean growth and in an unselected control line. Pigs of the three halothane segregants, NN, Nn and nn from both lines were grown on ad lib. feeding from 25 to 90 kg liveweight. Relative to the control, the selected line had faster, more efficient growth with lower 90 kg backfat thickness. Least square means in the selected and control lines were 0.87 and 0.77 ± 0.01 kg for daily liveweight gain, 2.63 and 2.98 ± 0.03 for food conversion ratio and 13.1 and 18.7 ± 0.3 mm for backfat. The halothane allele reduced appetite, growth rate, food conversion ratio and backfat. Means of the NN, Nn and nn segregants were 2.46, 2.31 and 2.10 ± 0.04 kg for daily food intake, 0.86, 0.84 and 0.78 ± 0.01 kg for daily liveweight gain, 2.89, 2.77 and 2.74 ± 0.03 for food conversion ratio and 16.7, 15.8 and 15.1 ± 0.4 mm for backfat. The average effect of the n allele on food intake and growth rate was higher in the selected than the control line. Mortality rates were increased by the halothane allele. Its effect on mortality was greatest in the selected line in summer while pigs were on road to the abattoir. Mean mortality rates were 1.4 ± 0.4, 2.6 ± 0.4 and 13.7 ± 1.1% for the NN, Nn and nn segregants.