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ANIMAL PRODUCTION |
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* Key Laboratory for Animal Biotechnology of Jiangxi Province and the Ministry of Agriculture of China, Jiangxi Agricultural University, 330045, Nanchang, China; and
Department of Biology, Jiangxi Science and Technology Normal University, 330038, Nanchang, China
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Key Words: enterotoxigenic Escherichia coli F4 adhesion phenotype • performance • pig • relationship
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). The bacteria adhere to their specific receptors on the brush border of epithelial cells in the small intestine. Colonizing bacteria synthesize enterotoxins that trigger secretion of water and electrolytes into the gut lumen of the small intestine and then lead to diarrhea (Chandler et al., 1994; Van den Broeck et al., 2000).
Susceptibility to F4 is inherited as an autosomal dominant Mendelian trait (Gibbons et al., 1977). Three antigenic variants of ETEC F4 have been described (F4ab, F4ac, and F4ad; Mooi and de Graaf, 1978). The locus determining susceptibility to F4ab and F4ac has been mapped to pig chromosome 13q41 (Joller et al., 2006), and several positional candidate genes and closely linked markers have been recently identified (Peng et al., 2007; Zhang et al., 2008).
Susceptibility to F4 is correlated with the F4 adhesion phenotypes, which can be determined with an in vitro microscopic brush border adhesion test (Baker et al., 1997). Six F4 adhesion phenotypes have been found in earlier studies (Baker et al., 1997; Python et al., 2005). More recently, we identified 2 novel adhesion phenotypes in Chinese indigenous pig breeds (our unpublished data). Studies of the relationship between the F4 adhesion phenotypes and performance traits in pigs are contradictory. Edfors-Lilja et al. (1986) reported that pigs with the F4ac receptor (F4acR, adhesive) had greater BW gain from 24 to 100 kg, whereas poorer daily gain during the first weeks of life than pigs without the receptor. However, this contradicts other studies in which no increased growth rates were observed for the presence of the F4 receptors (Gibbons et al., 1977; Baker et al., 1997). The aim of this study was to investigate the relationship of the F4 adhesion phenotypes with different performance traits in a White Duroc x Erhualian intercross population.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Animals and Measurement of Performance Traits
All experimental animals were from a 4-generation White Duroc x Erhualian intercross. In this pedigree, 2 White Duroc boars and 17 Chinese Erhualian sows were mated to produce 9 F1 sires and 59 F1 dams. These F1 animals were then intercrossed to generate F2 animals (n = 1,912) in 6 replicates, from which 62 F2 boars and 149 F2 sows were selected to produce 1,530 F3 animals. All piglets were weaned at 46 d and were then moved into a nursery (males were castrated at 90 d) where they received an ad libitum diet (on a DM basis) containing 21% CP, 3,300 kJ of DE, and 1.25% lysine until 120 d at the experimental farm of Jiangxi Agricultural University. Some animals were then transferred to a performance test station (Jiaoqiao, Nanchang, China), where an ACEMA 64 electronically auto-feed intake recording equipment (ACEMO, Pontivy Cedex, France) was used for measuring feed conversion ratio and feeding behavior. The other animals were raised at the original farm. During the study from 120 to 240 d, all animals were group-housed in pens each for 10 to 12 animals with an average of 2 m2 per pig. The ad libitum diet was changed to 16% CP, 3,100 kJ of DE, and 0.78% lysine. All diets were fortified with vitamins and minerals for approximate age of pig. Water was provided ad libitum. After the fattening period, animals at 240 ± 3 d were slaughtered in a commercial slaughter facility following Chinese industry standards.
Pigs were weighed at d 0, 46, 120, 210, and 240, and ADG during the sucking, fattening, and lifetime periods were calculated. Feed conversion ratios at these periods were measured for the animals (n = 97) raised in the performance test station. Backfat thickness at shoulder, chest, waist, and hip was measured with a vernier caliper after slaughter. Leaf fat, veil fat, and abdominal fat were weighed with an electrical balance. Longissimus muscle was taken from the left-side carcass within 30 min postmortem. The pH values of the LM between 11/14th ribs were recorded with a Delta 320 pH Meter (Mettler Toledo, Greifensee, Switzerland) at 45 min and 24 h postmortem. At the same time, muscle color and marbling were subjectively assessed according to the color standard (1 = pale; 6 = dark) and the subjective photographic reference standard provided by the US National Pork Producers Council, respectively.
Microscopic Brush Border Adhesion Test
Enterotoxigenic E. coli F4 strains 1496 (O139:K+:F4–), 195 (O8:K87:F4ab), 200 (O149:K91:F4ac), and 216 (O8:K87:F4ad) were purchased from the China Institute of Veterinary Drug Control (Beijing). Strain 1496 was used as a negative control. The ability of 3 variants (F4ab, F4ac, and F4ad) to express specific fimbriae was confirmed by agglutination assay before each assay as described previously (Osek and Svennerholm, 1991). An in vitro adhesion assay was performed as described previously (Zhang et al., 2008) to determine the ETEC F4 adherence phenotypes of 981 F2 animals in the White Duroc x Erhualian intercross in this study. Briefly, a 2-cm segment of the center part of the jejunum was collected from F2/F3 animals 30 min postmortem, and brush borders were isolated for the microscopic adhesion assay. The incubation of brush border and bacteria was then checked by phase contrast microscopy (Leica, Wetzlar, Germany). Twenty well-separated and intact brush borders were scored for each specimen. In cases in which less than 4 brush borders bound more than 2 bacteria, an additional 20 brush borders were examined. According to the criteria provided by Baker et al. (1997), a pig was classified as adhesive (susceptible) to ETEC F4 strains if at least 2 of 20 brush borders bound more than 2 bacteria. Pigs with all brush borders bound by less than 2 bacteria were judged as non-adhesive (resistant) animals. Otherwise when 2 bound, they were considered weakly adhesive animals.
Statistical Methods
The following model was used to evaluate relationships between F4 adhesion phenotypes and performance traits:
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where Yijk = the ijkth observation; µ = the general mean; bi = the fixed effect of the ith replicate; sj = the fixed effect of the jth sex; ak = the fixed effect associated with the kth F4 adhesion; and eijk = the random error effect of the ijkth animal. Moreover, BW was used as a covariate for growth traits, and carcass weight at 240 d was included as a covariate for fatness traits. The statistical analysis was performed with GLM procedure (SAS Inst. Inc., Cary, NC).
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RESULTS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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For each F4 strain, both adhesive and nonadhesive phenotypes were observed in the tested pigs. Most of the pigs of adhesive phenotypes had their brush border binding more than 2 bacteria. None of the nonfimbriated control bacteria bound brush borders. Animals with F4ab, F4ac, and F4ad adhesive phenotypes accounted for 30.3, 44.9, and 28.2% of the total population, respectively (Table 1).
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The relationships of the F4ab receptor (F4abR) adhesion phenotypes with the traits measured is shown in Table 1
. Pigs with F4abR (adhesive animals) had greater (P < 0.01) BW at birth, ADG at the testing period (from 46 to 240 d), and carcass weight and length than those lacking F4abR (nonadhesive animals). No difference was observed (P > 0.05) in G:F and traits related to meat quality and length of the small intestine between susceptible and resistant animals. Moreover, no difference was found (P > 0.05) in fatness traits including backfat thickness, weight of leaf, and veil fat except for the abdomen fat weight, which was heavier in pigs having F4abR.
Similarly, animals with the F4acR showed greater (P < 0.01) BW at 240 d, ADG during the fattening period, carcass weight, and length at 240 d than those lacking F4acR. No difference was observed (P > 0.05) in BW, ADG at the sucking period, G:F, fat deposition, meat quality, and length of the small intestine between 2 groups of pigs.
The F4ad adhesion phenotype displayed distinct relationships with performance traits compared with the F4ab and F4ac adhesion phenotypes. Pigs of the F4ad adhesive phenotype had smaller (P < 0.01) ADG during the fattening period, carcass weight, and fat deposition except for leaf fat than those having F4ad nonadhesive phenotype.
In total, 8 adhesion patterns including A (F4ab+, F4ac+, F4ad+), B (F4ab+, F4ac+, F4ad–), C (F4ab+, F4ac–, F4ad+), D (F4ab–, F4ac–, F4ad+), E (F4ab–, F4ac–, F4ad–), F (F4ab+, F4ac–, F4ad–), G (F4ab–, F4ac+, F4ad–), and H (F4ab–, F4ac+, F4ad+) were observed in the White Duroc x Erhualian intercross. The difference in performance traits between each adhesive pattern is given in Table 2. Notably, the adhesive phenotype B had a beneficial influence on production traits during the fattening period. Pigs of this phenotype were heavier (P < 0.01) at 240 d and had greater (P < 0.01) ADG during the fattening period and carcass weight and length compared with pigs of the nonadhesive phenotype (phenotype E). In comparison, animals having the adhesive phenotype D showed significantly less (P < 0.01) ADG during the fattening period than pigs of the phenotype E. No difference was found (P > 0.05) between adhesive and nonadhesive phenotypes regarding traits related to G:F, fatness, and meat quality.
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DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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and was inconsistent with the report by Baker et al. (1997).
Although pigs expressing F4ab/ac receptors have greater mortality rate during early life because of a greater susceptibility of neonatal diarrhea (Sellwood, 1979), our data indicated that pigs with F4abR or F4acR, or both, exhibited desirable production traits, which might influence their selection for use as breeding stock. The F4ab/ac receptors have been characterized as intestinal mucin-type sialoglycoproteins (Erickson et al., 1994), which cover the apical surfaces of epithelial cells in gastrointestinal tracts. The normal intestinal microbiota (e.g., lactobacilli and bifidobacteria) can recognize and bind intestinal mucin-type sialoglycoproteins to exert a barrier against attachment and colonization of pathogenic bacteria and to promote digestion and absorption of food (Meng et al., 1998). This could be the main reason that the F4ab/ac receptors have a beneficial effect on growth and development of pigs. In a modern breeding scheme, the culling of pigs with or without F4abR and F4acR might be a counterbalance of susceptibility to diarrhea and desirable production traits. In long-term selection, both susceptible and resistant phenotypes could be retained in a balanced selection. This hypothesis is consistent with the prevalence of F4 bacteria in different pig commercial populations. For instance, a large proportion (ranging from 37 to 80%) of pigs with the F4ab/ac adhesive phenotypes have been observed in Belgian (Cox and Houvenaghel, 1988), Australian (Snodgrass et al., 1981), and Americac (Baker et al., 1997) pig populations.
Pigs with F4abR showed greater ADG during the sucking period than those lacking the receptor. This contradicts the fact that the burden of colibacillosis has negative influence on growth of pigs with the receptor. The reason for this could be that the F4ac strain rather than F4ab is the main pathogen causing diarrhea in neonatal and early weaned pigs (Choi and Chae, 1999).
The influence of F4adR on growth in pigs was unknown before this study. These results revealed that pigs with F4adR had unfavorable production traits, showing poorer BW gain at the testing period and smaller carcass weight at 240 d. The F4adR showed a distinct effect on growth traits compared with F4abR and F4acR, which could be caused by different characteristic and function of these receptors. The F4adR is composed of a neutral glycosphingolipid (Grange et al., 1999), whereas F4ab/acR are intestinal mucin-type sialoglycoproteins (Van den Broeck et al., 2000). Because more pigs of the White Duroc-Erhualian cross have the F4adR, it may be implied that this receptor might have other unknown beneficial functions for survival or growth of the pig.
No difference in traits related to fatness, meat quality, and length of the small intestine was found between adhesive and nonadhesive phenotypes. This is in accordance with the previous reports (Edfors-Lilja et al., 1986). We did not observe a difference in G:F, a trait that is highly correlated with ADG. This could be due to limited number of animals measured for this trait (n = 97).
In summary, we evaluated the relationships between F4 receptors and performance traits in the White Duroc x Erhualian intercross, finding that the F4ab/ac receptors had a beneficial influence on growth traits during the fattening period and had no significant effect on length of the small intestine, meat quality, and fatness traits. This confirms the 2-sided effects of the F4ab/ac receptors: an undesirable effect on viability during the early life and a beneficial influence on performance during the fattening period, supporting the hypothesis that the prevalence of susceptible animals having the F4ab/ac receptors in Western commercial pig populations is attributable to balance selection.
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Footnotes |
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2 These authors contributed equally to this work and should be considered first co-authors.
3 Corresponding author: Lushenghuang{at}hotmail.com
Received for publication April 17, 2008. Accepted for publication August 13, 2008.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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