BREEDING & GENETICS
PIH-39
pork industry handbook
COOPERATIVE EXTENSION SERVICE • PURDUE UNIVERSITY • WEST LAFAYETTE, INDIANA
Crossbreeding Programs for Commercial Pork Production
Authors
Charles J. Christians, University of Minnesota
Rodger K. Johnson, Oklahoma State University
Reviewers
Pete Clark, Frankfort, Indiana
Kenneth Drewry, Purdue University
Irvin Omtvedt, University of Nebraska
Crossbreeding is a widely accepted and recommended practice in commercial swine production. Nearly 90% of our commercial producers raise crossbred hogs for slaughter. Although breed selection is important, to capitalize on heterosis, genetic improvement will come basically through selection of superior sires from within each breed.

Crossbreeding is used to combine desirable characteristics of different breeds and to capitalize on hybrid vigor (heterosis). Heterosis is defined as the average superiority of the crossbred progeny over the average of their parents. When crossbred pigs perform above the average of the two parental breeds, heterosis results (Fig. 1). This superiority may be more (Fig. 1) or less (Fig. 2) than one of the breed’s performance, depending on the breeds crossed; however, it must be above the parental average. When the crossbred pigs perform at parental breed average, no heterosis exists.

Heterosis occurs when genetically different lines or breeds are crossed, and it is greatest for traits with low heritabilities. Traits such as litter size, litter weaning weight and survival rate respond best to crossbreeding. Carcass traits are highly heritable and are not improved by crossbreeding (Table 1). If the crossbred is to produce an excellent carcass, both parents must have superior carcass characteristics.

When a boar of a different breed is used on purebred dams, litter size (0.5%) is not significantly increased (Table 1). Since the mother breed in the original cross will influence litter size, breeds that are noted for large litters should be used as foundation females.
Even if litter size at farrowing is not increased, purebred sows will wean about 10% more crossbred than purebred pigs. A greater survival rate results from heterosis responses in the crossbred pigs. A 24% increase in litter weaning size can be expected when a crossbred sow is
used. This improvement is due to an increased number of pigs born alive and greater baby pig survival to 21 days.

Pig survival and growth are the real benefits of a systematic crossbreeding program. When crossbred sows are used, about 28% greater 21 -day litter weights can be realized per female exposed as compared to purebreds.
Table 1. Average percent heterosis advantage for various swine traits.*
Trait	First cross using purebred female.^	Multiple cross using crossbred female.^^
	               % advantage over purebreds	
          Reproduction		
No. pigs born alive	0.5	8.0
Litter size—21 days	9.0	23.0
Litter size—weaning	10.0	24.0
          Production		
21 -day litter wt.	10.0	27.0
21 -day litter wt. /female exposed	5.0 28.0	
Days to 220 lb.	7.5	7.0
Feed/lb. gain	2.0	1.0
          Carcass composition		
Length	0.3	0.5
Backfat	1.5	1.5
Loin eye area	1.0	2.0
Marbling score	0.3	1.0
* Composite results from Oklahoma and Iowa NC-103 regional swine project.
^ 997 litters using Duroc, Chester, Hampshire, Yorkshire breeds and all possible crosses.
^^ 611 litters using Duroc, Chester, Hampshire, Yorkshire breeds and all possible crosses.
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, IN. 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, color, sex. religion, national origin, age or handicap.