Effects of Inbreeding, Selection, Linecrossing and Topcrossing in Swine. II. Linecrossing and Topcrossing

Abstract

Results are presented from an experiment in which inbred lines of swine were tested in linecross and topcross combinations in an experimental breeding herd and in which inbred and linecross boars were compared with outbred boars in two-sire farm herds. Data from 270 litters farrowed in 4 years were studied in the 1st part of the experiment. The farm topcross tests involved a total of 1648 litters in 93 herds over an 8-year period. Data from 228 litters in 14 of these herds were analyzed separately because the effect of topcrossing could not be separated from that of cross-breeding. Linecrossing resulted in a recovery of the vigor lost during inbreeding, but showed no average advantage for the linecrosses over outbred controls. Topcrosses by inbred boars carrying Landrace breeding were significantly heavier by 11 pounds at 5 months of age than non-topcrosses in the same herds. No other topcrosses by inbred boars showed any significant advantage in viability or rate of gain. Top-cross gilts by inbred boars were consistently superior to their controls in size and weight of litters raised to 5 months. Results from 27 herds showed significant increases for the topcross gilts of 1.0 pig and 156 pounds in these 2 traits respectively. There was an indication that in-bred and linecross boars differed in their performances in topcrossing.