[Breeding adaptation to avoid antagonisms between production and health in swine]

Lerner (1954) with his hypothesis of genetic homeostasis has provided the explanation for most of our present antagonism-problems in high performing farm animal populations. Effective artificial selection for highly heritable traits (such as lean content and muscularity in pigs) leads to negatively correlated responses in other traits, particularly the components of reproductive fitness. There are three main antagonisms in our present breeding populations of meat type pigs, which are all caused by the dramatic genetic changes in lean content and muscularity: 1. Poor meat quality and high stress susceptibility. 2. Decreasing reproductive performance. 3. Increased leg weakness problems. The most efficient breeding strategies against these antagonisms are 1. Elimination of the recessive Halothane stress gene from at least one parental population by systematic progeny test procedures. Crossbred progeny from one homozygous stress resistant parent are at least heterozygous stress resistant and have good meat quality. 2. Use of crossbred sows from two parental breeds leads on an average of 10% to a better litter performance than purebred sows. Hybrid sows from selected dam lines can have a markedly better litter performance than 10%. 3. Avoidance of extreme muscularity or carcass length as well as tests and the selection of the breeding stock under practical (strawless) management conditions reduces the incidence. Moreover crossbred boars from unrelated parent breeds show much less leg and libido problems.