|Hong, Yeong Ho -|
Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 15, 2009
Publication Date: February 1, 2010
Citation: Kim, E., Hong, Y., Lillehoj, H.S. 2010. Genetic effects analysis of MLF2 and TCR-B on resistance to coccidiosis in chickens. Poultry Science. 89:20-27. Interpretive Summary: Avian coccidiosis is caused by ubiquitous intestinal protozoan that significantly impair the growth and feed efficiency of infected chickens. Although coccidiosis has been under control by coccidiostatic drugs, vaccination and genetic selection , emergence of coccidiosis resistant strains is decreasing the effectiveness of approaches. Finding genes associated with coccidiosis resistance will be useful to efficient genetic selection for disease resistant lines and understanding mechanisms underlying disease resistance in chickens . In this report, ARS scientists used QTL mapping studies to identify genes associated with disease resistance to avian coccidiosis, a parasitic disease caused by several distinct species of Eimeria. Resistance to coccidiosis can be considered as multigenic trait based on the variation of sickness after infection with Eimeria . Using the methods of evaluating resistance or susceptibility to coccidiosis by multiple phenotypic measurements, the current study was conducted to identify SNPs that may play a role in the host response to coccidia infection defined by oocyst shedding. The current results showed that a statistically significant association between five SNPs in two genes (MLF2 and TCR-ß) and oocyst shedding which is major index for the resistance to avian coccidiosis. In addition to oocyst shedding, associations between SNPs in MLF2 and body weight support the relationship between MLF2 and coccidiosis resistance. Single marker association analysis for 16 traits of coccidiosis resistance showed that a TCR-ß SNP and two MLF2 SNP were significantly associated with oocyst and body weights. Development of additional markers for candidate genes relevant to protective immunity will enhance feasibility of developing coccidiosis-resistance chickens.
Technical Abstract: Associations between parameters of resistance to coccidiosis and single nucleotide polymorphisms (SNPs) in three candidate genes located on chromosome 1 (TCR-ß, MLF2, and Lymphotactin) were determined. SNPs were genotyped in 24 F1 generation and 290 F2 generation animals. Four SNPs were identified in the Lymphotactin gene, 10 were located in the TCR-ß gene and 4 in the MLF2 gene. At various times following experimental infection of the F2 generation with Eimeria maxima, body weights, fecal oocyst shedding, and biochemical parameters were measured as parameters of resistance. Single marker association test was applied to determine the associations between the 20 SNPs and the parameters of coccidiosis resistance. The maximum allele substitution effect on disease resistance of a SNP in MLF2 was explained by body weight (p = 0.0002). The SNP in MLF2 significantly associated with body weight was also associated with both oocyst shedding (p = 0.001). Four SNPs associated with oocyst shedding were found within coding region of TCR-ß. While none of the Lymphotactin SNPs was associated with oocyst shedding, interferon-' level was associated with 2 SNPs in Lymphotactin. These results suggest that MLF2 is a potential gene associated with resistance to experimental avian coccidiosis.