BREEDING & GENETICS
PIH-27
pork industry handbook
COOPERATIVE EXTENSION SERVICE • PURDUE UNIVERSITY • WEST LAFAYETTE, INDIANA
Guidelines for Choosing Replacement Females
Authors
William T. Ahlschwede, University of Nebraska
Robert H. Grummer, University of Wisconsin
Reviewers
C. Melvin Fink, University of Illinois
Ron Liittjohann, Wiggins, Colorado
Grant Sherritt, Pennsylvania State University
The productivity of the sow herd is the foundation of commercial pork production. The sow herd also contributes half of the genetic makeup of growing-finishing pigs. These factors together indicate the importance of careful selection of replacement gilts and wise decisions on their retention in the sow herd. It is recommended that the fastest growing, leanest gilts that are sound and from large litters be kept for sow herd replacements. Among sows which have farrowed and will rebreed, only sows with physical problems, bad dispositions, extremely small litters (2 pigs below herd average) and poor mothering records should be culled.

The Sow’s Job
For a commercial pork operation to be successful, the sow herd needs to wean large litters of pigs regularly. This means that a large percentage of the sows and gilts show estrus and breed, farrow large litters of vigorous pigs, keep a high percentage of the pigs alive and get their pigs off to a good start. All of these functions are affected in large part by environmental situations and management practices. Although differences among breeds for these traits are apparent, the genetic influence is such that no direct selections can be made among replacement gilts for these functions.

The size of litter in which a gilt is born and the weaning weight of the litter genetically are traits of the gilt’s mother. Selecting gilts for these traits would be selection on the dam’s record, which dilutes the selection effort. Our understanding of the genetic basis for these traits indicates that economically important genetic changes can be made by selection. The large non-genetic variation in these traits, particularly litter size, makes it difficult to detect the change.
Keeping baby pigs alive and getting them off to a good start generally are classed as maternal effects. Successful management schemes usually assign the job of keeping
Cooperative Extension Work in Agriculture and Home Economics, State of Indiana, Purdue University and U S Department of Agriculture Cooperating. H. G. Diesslin, Director, West Lafayette, Ind. Issued in furtherance of the Acts of May 8 and June 30, 1914. It is the policy of the Cooperative Extension Service of Purdue University that all persons shall have equal opportunity and access to its programs and facilities without regard to race, religion, color, sex or national origin.