BREEDING AND GENETICS
PIH-58
pork industry handbook
COOPERATIVE EXTENSION SERVICE • PURDUE UNIVERSITY • WEST LAFAYETTE, INDIANA
Selection Guidelines For The Seedstock Producer
Authors
Gene A. Isler, Ohio State University
Lauren Christian, Iowa State University
Reviewers
Ben Bereskin, USDA, Beltsville, Maryland
Carl Hirschinger, University of Wisconsin
R. Keith Leavitt, University of Missouri
Max Waldo, DeWitt, Nebraska
The seedstock industry is undergoing a revolution which emphasizes supplying genetic material to more adequately meet the needs of the commercial producer. This is the sole purpose of its existence. The dynamic nature of the commercial industry has dictated the need for this change and for reassessment of priorities by the seedstock supplier. If the progressive seedstock producer expects to continue to be a viable force in the pork industry, his goals should include the following:
•	Supply the genetic material for the production of healthy, fast growing, efficient, lean and high quality pigs.
•	Provide animals capable of conceiving and raising large litters of uniform, thrifty pigs.
•	Produce seedstock with the structural soundness necessary to breed and perform under a wide range of environmental conditions.
•	Maintain sufficient production volume to insure year-round availability of stock.
•	Provide seedstock that will permit the commercial producer to maximize heterosis and utilize the superior characteristics of each breed or strain through systematic use of them in a crossing program.

Traits to Measure
Sow Productivity Traits
Litter size, number reared per litter, total litter weight at 21 days and litters per sow per year have generally been considered lowly-heritable traits. Because of their immense economic importance, these traits can be improved upon or maintained at satisfactory levels within seedstock populations by removing families extremely low in performance, keeping the rate of inbreeding low, and selecting sows with superior records. Some selection pressure on litter size is automatic since more selection choices exist in larger litters.

Attention to these traits is warranted, especially in breeds chosen by commercial producers primarily for their desirable maternal characteristics. Equalizing litters, when
possible, to approximately 10 live pigs to provide every sow with the opportunity to raise a standard number and to provide subsequent measurement of 21-day litter weight (a trait largely a function of milk production) should provide an equitable method for measuring mothering ability. This also provides an opportunity for young gilts to develop unhampered by the "competitive effects" of being raised in very large litters.

Emphasis on number of live pigs farrowed per litter (NBA) is a measure of prolificacy. (See Figure 1). This
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.