BREEDING & GENETICS
PIH-39
pork industry handbook
PURDUE UNIVERSITY • COOPERATIVE EXTENSION SERVICE • WEST LAFAYETTE, INDIANA
Crossbreeding Systems for Commercial Pork Production
Authors:
William T. Ahlschwede, University of Nebraska
Charles J. Christians, University of Minnesota
Rodger K. Johnson, University of Nebraska
O. W. Robison, North Carolina State University
Reviewers:
Russell and Jane Clark, Frankfort, Indiana
Walter A. Gross, University of Rhode Island
James and Shirley Mitchell, Eaton, Ohio
Irvin Omtvedt, University of Nebraska
Years of experience and research show that crossbreeding pays. The hybrid vigor gained through crossbreeding improves performance of both the breeding herd and individual pigs. Surveys indicate that more than 90% of market hogs in the U.S.A. are crossbreds. However, crossbreeding is not sufficient to assure profitable performance. Rather, specifying which breeds to cross and how to cross them is needed to describe a crossbreeding system. Choices among crossbreeding systems can dramatically affect profit levels.

The value of crossbreeding depends upon hybrid vigor. Hybrid vigor, or heterosis, is the superiority of the crossbred compared to its parental breeds. In pigs, hybrid vigor appears important for pig survival and growth, litter size and mothering ability in sows and gilts and boar breeding performance (Table 1). Differences in performance among breeds can be utilized by some crossbreeding systems to take advantage of the best attributes of breeds while minimizing the impact of their deficiencies.

Crossbreeding became a common practice as a result of crossbreeding research in the 1930’s and 1940’s. Crossbred offspring of purebred parents were indeed superior. Following the lead of corn growers, crossbred females became the base of commercial production. However, with pigs, development of inbred lines did not prove feasible. Rotational crosses, which nicely fit the most common styles of production in the 1950’s and 1960’s, were generally adopted. Changes in the way hogs are produced have led to increased adoption of terminal crosses in the 1980’s.
Rotational Crosses
Two general types of crossbreeding systems are described. Rotational crossbreeding systems utilize replacement gilts from the market crosses and change breeds of boar each generation. A three-breed-rotation uses three
breeds of boars, rotated in order, one breed per generation (Figure 1). A rotation of two breeds is called a criss-cross. Rotations of up to six breeds have been used to advantage.

Rotations using crossbred boars take advantage of hybrid vigor in boar breeding ability. After the first full round of breeds in a rotation, some heterosis is lost. To the degree that genes of the breed of the service boar are present in the sow, heterosis is reduced. As shown in Table 2, rotations of three or more breeds retain relatively high levels of heterosis. Serious losses of heterosis in rotations occur when the planned order of breed use is not followed. This is likely when generations of sows are not kept
Table 1. Heterosis advantage for production traits.			
Item	First cross purebred sow	Multiple cross crossbred sow	Crossbred boar
	Percentage advantage over purebred		
Reproduction			
Conception rate	0.0	8.0	10.0
Pigs born alive	0.5	8.0	0.0
Littersize 21 days	9.0	23.0	0.0
Littersize weaned	10.0	24.0	0.0
Production			
21-day litter weight	10.0	27.0	0.0
Days to 220 lb.	7.5	7.0	0.0
Feed/gain	2.0	1.0	0.0
Carcass composition			
Length	0.3	0.5	0.0
Backfat thickness	-2.0	-2.0	0.0
Loin muscle area	1.0	2.0	0.0
Marbling score	0.3	1.0	0.0
			
Cooperative Extension work in Agriculture and Home Economics, state of Indiana, Purdue University and U. S. Department of Agriculture cooperating.  H. A. Wadsworth, Director, West Lafayette, IN. Issued in furtherance of the Acts of May 8 and June 30, 1914. The Purdue University Cooperative Extension Service is an affirmative action/equal opportunity institution.