An embryo transfer study of reciprocal cross differences in growth and carcass traits of Duroc and Landrace pigs.

Reciprocal cross differences have been reported for growth rate and carcass traits in F1 pigs with the Duroc (D1 as a parent breed. Such differences are synonymous with maternal effects if effects of sex linkage and genomic imprinting are negligible. In the present study, transfer of embryos (ET1 to paternal breed recipients parti- tioned effects occurring at or before fertilization from postfertilization effects for growth and car- cass traits in F1 D-Landrace (Ll pigs. Fifteen boars sired 115 F1 litters, 49 produced by ET. Growth rate of 349 barrows and 361 gilts and carcass measure- ments on 256 barrows and 159 gilts were analyzed assuming mixed linear models with animal and litter as random effects. Contrasts among geno- type (D x L, L x D) - treatment (ET, non-ET) means were tested. Reciprocal cross differences were not detected for growth rate or for carcass weight, length, average backfat thickness, estimated car- cass lean, or lean per day of age. Reciprocal cross differences for loth rib backfat thickness (BFI and longissimus muscle area (LMA) were detected only in barrows. The sexual dichotomy for reciprocal cross differences followed expectations for a Y- linked gene(s1, consistent with the fact that recip- rocal D - L crossbred barrows exhibited a paternal effect, with responses more like the sire breed than the dam breed. Barrows that were non-ET from D sires and L dams had 3.9 cm2 larger LMA and 5.8 mm less BF than barrows from L sires and D dams P .lo) than barrows sired by L boars reared by L dams (ET). In conclusion, reciprocal cross differences detected for BF and LMA in barrows were established before or at fertilization and seemed to be Y- linked.