Summary Associations between production traits and the genes for halothane sensitivity (HAL), S, A and H blood group systems and phosphohexose isomerase (PHI) and 6-phosphogluconate de- hydrogenase (6-PGD) enzyme systems were investigated in two lines of pigs selected for an index. The phenotypic variance-covariance matrix of the index included backfat thickness and daily gain, whereas the genetic variance- covariance matrix included daily gain, feed conversion and percentage of lean meat. The experiment was conducted at the experimental station of the Institute of Animal Produc- tion and has been underway since 1973. The same index was applied but in two opposite directions to give a superior and inferior line in relation to the production traits. One hundred twenty-nine animals of the superior line in the seventh generation and 88 animals of the inferior line in the sixth generation were studied. Forty-two percent (54/129) of the animals of the superior line were halothane- positive. No animals in the inferior line were halothane reactors. Of the halothane-positive pigs, 70.4% (38/54) in the superior line had the Hall a and 94.4% (51/54) had the SsSS geno- type, whereas only 4% (_3/75) of the Hall a and 12% (9/75) of the Sss s pigs were halothane- negative. By practicing selection at the H and S loci, it seems possible to efficiently reduce halothane sensitivity in Swiss Landrace pigs. In pigs of the superior line, there were significant differences in percentage of lean meat, carcass length, pill (pH value at 45 min to 1 h postmortem, M. longissimus) and reflec- tance values among genotypes of the HAL, S and H systems and among some genotypes of the 6-PGD system. Poorest meat quality, highest percentage of lean meat and shortest carcass length were observed in pigs homozygous for the alleles HAL n, S -~, Ha, PHIB and 6-PGDA. In the inferior line, these associations were absent. As the HAL locus is associated with the above mentioned production traits, linkage disequilibria may explain the observed asso- ciations among the H, S, PHI and 6-PGD types and production traits.

To clarify the relationship between growth, carcass characteristics as well as meat and fat quality opposite to genotype and feeding regimen, three crossbred genotypes were performance tested. Moreover this experiment was expected to render information about the economical result of the crossbred genotypes. The sire breeds were chosen according to their differences in meat performance: Piétrain (PI) represented a lean type, the Swiss Large White (LW) stood for an intermediate and Duroc (DU) for a less meaty type. The Swiss Landrace (SL) was used as dam breed. 500 crossbred animals were tested under three different feeding intensities (low = RAT, medium = ALR, according to appetite e.g. ad lib = ADL) from 25 to 103 kg live weight. According to the experimental plan, lean meat content was mainly determined by genotype, whereas feed intake and average daily gains were influenced above all by feeding regimen. When fed to scale, a smaller maintenance requirement for less meaty types could be established. Lower feed consumption in PI x SL crosses was connected with reduced daily gains, less subcutaneous and intramuscular fat, but also with higher lean meat content and a lower feed conversion ratio. Meat quality was mainly determined by genotype, only intramuscular fat content and fat quality traits were influenced by the feeding regimen. Production of first quality pig meat requires a restricted lean meat content and an increased daily intake. Considering fat quality traits, an optimal feed conversion ratio must be established. An increase of average daily gain does not seem to have any negative effect on the meat quality traits investigated. Under conventional payment systems meaty animals of the PI x SL cross had the highest gross margins. It was concluded that a quality paying system including on one hand lean meat content and on the other meat and fat quality traits tends to minimize the differences in the gross margins between different genotypes.

Associations between production traits and the genes for halothane sensitivity (HAL), S, A and H blood group systems and phosphohexose isomerase (PHI) and 6-phosphogluconate dehydrogenase (6-PGD) enzyme systems were investigated in two lines of pigs selected for an index. The phenotypic variance-covariance matrix of the index included backfat thickness and daily gain, whereas the genetic variance-covariance matrix included daily gain, feed conversion and percentage of lean meat. The experiment was conducted at the experimental station of the Institute of Animal Production and has been underway since 1973. The same index was applied but in two opposite directions to give a superior and inferior line in relation to the production traits. One hundred twenty-nine animals of the superior line in the seventh generation and 88 animals of the inferior line in the sixth generation were studied. Forty-two percent (54/129) of the animals of the superior line were halothane-positive. No animals in the inferior line were halothane reactors. Of the halothane-positive pigs, 70.4% (38/54) in the superior line had the HaHa and 94.4% (51/54) had the SsSs genotype, whereas only 4% (3/75) of the HaHa and 12% (9/75) of the SsSs pigs were halothane-negative. By practicing selection at the H and S loci, it seems possible to efficiently reduce halothane sensitivity in Swiss Landrace pigs. In pigs of the superior line, there were significant differences in percentage of lean meat, carcass length, pH1 (pH value at 45 min to 1 h postmortem, M. longissimus) and reflectance values among genotypes of the HAL, S and H systems and among some genotypes of the 6-PGD system. Poorest meat quality, highest percentage of lean meat and shortest carcass length were observed in pigs homozygous for the alleles HALn, Ss, Ha, PHIB and 6-PGDA. In the inferior line, these associations were absent. As the HAL locus is associated with the above mentioned production traits, linkage disequilibria may explain the observed associations among the H, S, PHI and 6-PGD types and production traits.

An experiment with pigs, using a selection index, combining the scores for backfat thickness and daily gain has been conducted since 1973. The population was divided into two lines, on which the selections were made. The same index was applied in both lines, but in opposite directions, to give a positive and a negative line. Thus, 251 animals of the positive line in the seventh generation and 89 animals of the negative line in the sixth generation were studied.