SUMMARYThe inheritance of reaction to halothane anaesthesia (so-called malignant hyperthermia syndrome) in pigs was studied in a series of 61 litters by 18 sires from an F3–F4 Pietrain–Hampshire crossbred population. A single locus two allele model allowing for reactors from all three genotypes, was fitted by maximum likelihood. It was concluded that the reaction is due to a single autosomal recessive gene with a frequency of 0·46 (0·44–0·48) and penetrance of 0·95 (0·92–0·98) in this stock.

The data used in these analyses were compiled from individual feeding records of 1832 pigs from 70 sire families using FIRE (food intake recording equipment) system from Hunday Electronics Ltd at the Cotswold Pig Development Company. Pigs were on test between 45 (s.d. 2·76) kg and 95 (s.d. 6·78) kg. Daily food intake (DFI kg), food intake per visit (FlV kg), number of visits per day (NV), duration of each visit (TV min), time in the feeder per day (TD min), feeding rate (FR kg/min) and number of non-feeding visits per day (NFV), were measured as means of test and DFI was also recorded as means of bi-weekly periods of test. Performance test traits ofbackfat depth off test (BF mm), food conversion ratio (ECR kg/kg) and average daily gain (ADG kg), over the test period, were also measured.Parameters were estimated by restricted maximum likelihood with a multivariate individual animal model. DFI had a heritability of 0·21 ranging from 0·18 to 0·26 over the four test periods. Correlations between DFI in each test period were high (rg = 0·75 to 0·99). DFI was highly correlated with performance test traits (0·61 to 0·78) but had low correlations with feeding pattern traits (0·0 to 0·24). The heritabilities of feeding pattern traits were low (0·06 to 0·11) with the exception of FIV (0·27) and NV (0·34) but correlations between feeding pattern traits were high. FIV, NV and TV were moderately correlated with ADG (rg = 0·49, -0·29, 0·33 respectively), BF (rg = 0·35, -0·15, 0·17 respectively) and ECR (rg = -0·12, 0·31, -0·27 respectively). Feeding patterns may be changed substantially by selection and the genetic correlations with performance test traits indicate that feeding patterns traits can be usefully incorporated in selection criteria to improve somewhat the accuracy of selection.

Data from 14 074 gilts, performance-tested on 66 farms, were matched with those from 3835 station-tested boar sibs, the whole comprising progeny test results on 456 sires. Both groups of data were adjusted independently for effect of month of test and the farm data further adjusted to a constant weight of 91 kg. Analysis of variance and covariance was carried out within herds using weighted sire progeny means. Phenotypic correlations between the same traits recorded 'on-farm' and in station, ranged from 0-12* (weight/ age) to 0-25** ('C' + 'K' fat depth) while genetic correlations, computed using the estimated accuracy of each test, ranged from 0-23* (weight/age) to 0-49** (simple performance test index). Correlations were generally higher in Large White than in Landrace pigs. 1 1 8 H z 0°• d § t = Percentage lean in rump back.

Data were extracted from Meat and Livestock Commission records from 44 herds with 392 progeny-tested sires in both farm and station environments. The farm data contained 4182 and 17 251 male and female progeny respectively, and the station data 2982 and 1490 male and female progeny respectively. Both sets of data were adjusted separately for the effects of month of test within sex. The farm data were also corrected to a constant end-of-testweight corresponding to that at the station. Comparisons were made between both different and the same sexes in the two environments. Phenotypic correlations between a simple index measure in both environments ranged from +0-20 (farm females:station males) to +030 (farm females:station females). Genetic correlations between similar traits ranged from -018 (weight/age, farm males:station females) to +081 (simple index, farm males:station females). The correlations between female farm progeny and station male progeny were generally lower than for any other comparisons.