Crossbreeding and Hybrid Vigor

Niche Pork Production Reproduction and Genetics

Authors Crossbreeding and Hybrid Peter J. Lammers David R. Stender Vigor Mark S. Honeyman IPIC NPP410 2007

How pigs perform is the result of two ♦ Berkshire Better in conception rate, influences: genetics and environment. The intramuscular fat, and pork quality. genetics or heredity of a pig sets the upper More backfat. limit or potential of its performance. The ♦ Chester White Better in conception environment of a pig sets the actual level of rate, litter size weaned, and growth rate. performance. Environment includes the ♦ Duroc Better in growth rate, pigs’ surroundings, the feed, and the intramuscular fat, and pork quality. diseases it encounters. The genetics of a pig More backfat. are passed from the boar and sow that ♦ Hampshire Less backfat and lean pork. produce the pig. The pig producer has two ♦ Landrace Better in litter size weaned, primary tools to influence the genetics of a litter weight. More backfat. pig: selection and hybrid vigor. ♦ Poland More backfat. ♦ Selection is the process of picking which Spotted Better in growth rate. ♦ breeds or lines of pigs to use and which Yorkshire Better in litter size weaned, litter weight, and growth rate. individuals within the breed to mate. 1 Based on NC-103 and NPPC NGEP, 1995. Breeds There are eight major U.S. swine breeds Heritability of traits plus several minor breeds. There are also Individual boars and sows pass on traits many lines that have been developed by to their offspring based on the heritability of commercial swine companies. The three the traits (Table 1). The maternal/ white breeds, Yorkshire, Landrace and reproductive traits have low heritability Chester White are known for maternal traits, about (5 to 30%). The growth traits are i.e., they excel as sows with large litters. The moderately heritable (24 to 30%), and the five dark breeds, Duroc, Hampshire, Poland carcass traits have high heritability (40 to China, Spotted and Berkshire, are known for 60%). Pork quality traits are moderately carcass or terminal traits, i.e., they excel as heritable (15 to 30%). Traits with a low boars to produce market pigs. In niche heritability change more slowly due to markets, Berkshire and Duroc breeds are selection than traits with a high heritability. often used because they excel in meat Heterosis quality traits. Hybrid Vigor (or heterosis) is the Breed Attributes1 improved performance of offspring There is considerable variation within a compared to the average of their parents. breed, however there are some differences Hybrid vigor is maximized by crossing between breeds. different breeds or lines. This is known as crossbreeding. Hybrid vigor is greatest for reproductive and early pig survival/growth traits. Most sows and market pigs in the U.S. are crossbred pigs. Table 1. Estimates of heritability of traits1 For example a Berkshire boar mated to a Reproductive traits Yorkshire x Duroc sow would produce pigs Conception rate 30% that are ½ Berk, ¼ York, ¼ Duroc (Diagram Pigs born alive 10% 1). Litter birth weight 30% Prewean survival 5% Pigs weaned 7% Weaning weight 17% Rebreed Interval 23%

Growth traits Average daily gain 30% Feed/Gain 30% Average daily feed intake 24%

Advantages Carcass traits Simple to manage Backfat 50% 100% hybrid vigor Loin muscle area 45% Genetically uniform pigs from year to year Lean percent 48% Crossbred sows

Uses breeds where their strengths exist Pork quality traits (terminal or maternal) Pork color 28% Works well for small herds Muscle pH 21%

Drip loss 16% Disadvantages Tenderness 26% 1 Replacement gilts must be introduced to the Adapted from PIH 06-01-05. herd (usually purchased) Gilt availability Gilts may introduce disease Crossbreeding Strategies Gilt cost Crossbreeding systems are designed to maximize hybrid vigor. Crossbred sows are especially advantageous with better 2) Rotation System conception rates, more pigs born and Rotation cross systems involve rotating weaned, and heavier litters than purebred breeds of boars each generation. Usually sows. For extensive niche pork production two, three, or four breeds are used in settings (outdoor or in hoop barns), a rotation. When the rotation is complete, the crossbred sow with some dark breed first breed in the rotation is used again and ancestry may be more rugged and durable the sequence repeats. Replacement gilts are than an all-white sow. There are three basic saved from the pigs and bred to the breed of crossbreeding systems. boar next in the sequence. A typical 3-breed rotation used by niche pork producers is a 1) Terminal System Berkshire/Yorkshire/Duroc sequence Terminal cross systems usually use a (Diagram 2). boar (purebred or crossbred) on crossbred sows of different breeds. All the pigs are marketed. Replacement gilts are purchased.

Page 2 IPIC NPP410 2007 Advantages Simple to manage Disadvantages Replacement gilts are produced in herd Somewhat complicated to manage Crossbred sows Requires about 200 litters per year to work Boars or semen are only addition to the herd Less than 100% hybrid vigor in sows Less risk of bringing disease into herd Less genetically uniform pigs from year to Works well for small herds year and within a year Maternal white barrows and cull gilts may Disadvantages require a separate market Less than 100% hybrid vigor 2-breed has 67% PHV Each system has its own advantages and 3-breed has 86% PHV disadvantages. Beginning niche pork 4-breed has 92% PHV producers should use either the terminal or (PHV = possible hybrid vigor) rotation approach, based on whether they Less genetically uniform pigs from year to plan to raise or purchase replacement gilts. year Remember to always isolate incoming Breeds must be dual-purpose (both terminal breeding stock for 30-60 days and consult and maternal) with your veterinarian about tests and vaccinations before mixing the new stock 3) Combination or Rotaterminal System with your herd. By combining the terminal and rotational systems, the advantages of both can be achieved. A few of the sows are bred rotationally to maternal boars to produce replacement gilts, and the rest of the sows are Additional Resources bred to terminal boars to produce market pigs. Iowa Pork Industry Center. 109 Kildee Hall. Iowa State University, Ames, IA, 50011. Advantages 515-294-4103. Replacement gilts are produced within the in Iowa: 1-800-808-7675 herd http://www.ipic.iastate.edu/about.html Crossbred sows

Boars or semen are only addition to herd U.S. Pork Information Gateway Less risk of bringing disease into herd http://pork.porkgateway.org/web/guest/home 100% hybrid vigor in market pigs Uses breeds where their strengths exist (terminal or maternal)

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