Genetic resistance of pigs to neonatal enteritis caused by E. coli
Genetics Selection Evolution
some reason had been excluded from the testing. After this merging exactly io 00o individuals remained. The disease records and certain production traits have been analysed statistically, whereby the health registrations were regarded as all-or-none traits (o = healthy, I = sick), i.e. the degree of affection is disregarded. The results from these analyses shows that Landvace pigs seems to have far fewer lung lesions than Yovkshive, whereas the relation for AR is with weak significance the
... gnificance the reverse. The sex differences indicate that castrates are somewhat more susceptible to the infectious diseases than gilts are. The heritability estimates for the diseases, considered as all-or-none traits lie between 0 . 12 and o.r4. The phenotypic correlations between lung-and snout lesions and production traits show that generally speaking a disease pig grows more slowly, is leaner, has a smaller M. Longissimus dorsi area and has rather more meat in the side, compared with healty animals. The strains of E. coli which are usually associated with neonatal diarrhoea in the piglet possess the K88 antigen. This antigen is a virulence determinant and it functions as such by adhering the organisms to the intestine of the piglet. In some pigs the gut cell receptor for K88 is absent, K88 positive organisms do not attach themselves to the intestinal wall of these pigs which animals are therefore almost wholly resistant to the disease. Resistance is inherited as a simple autosomal recessive designated s; the dominant allele S conferring adhesiveness and disease susceptibility on the animal. In spite of the advantage conferred upon the homozygous recessive ss neonate, allele S seems common, indeed predominant. The probable reason for this paradox lies in the relative failure of ss sows to respond immunologically to the K88 positive E. coli in the gut. This causes heterozygous piglets out of homozygous recessive sows to be at a large disadvantage compared with all other piglets. Since s is the less common allele, selection against this heterozygote tends to eliminate it. Despite the prevalence of allele S, there is no disadvantage to s unless S is also present in the same breeding population; the ss animal should therefore be economically valuable. Mortality data of 3 Leghorn lines and their crosses from the years 1972 , 1973 and 1975 , totalling about 12 ooo female offsprings from more than 150 sires and 2 ooo dams were analysed. The hens were kept in the Institute for Small Animal Research at Celle under conditions of normal exposure to disease. The investigation leads to the following results: i) Most mortality traits were influenced by the line combinations as well as paternal-and maternal-line effects. 2 ) Even under conditions of normal exposure crossbreds had less mortality than purebreds. 3 ) For Marek Disease heritability estimated on a " liability " scale seems to be such that it is worthwhile to seek for a normally distributed alternative trait when selecting for livability.