Genetics of tuberculosis in Irish Holstein-Friesian dairy herds

Abstract

Information is lacking on genetic parameters for tuberculosis (TB) susceptibility in dairy cattle. Mycobacterium bovis is the principal agent of tuberculosis in cattle. The objective of this study was to quantify the genetic variation present among Irish Holstein-Friesian dairy herds in their susceptibility to M. bovis infection. A total of 15,182 cow and 8,104 heifer single intradermal comparative tuberculin test (SICTT, a test for M. bovis exposure and presumed infection) records from November 1, 2002, to October 31, 2005, were available for inclusion in the analysis. Data on observed carcass TB lesions from abattoirs were also available for inclusion in the analysis. The only animals retained were those present in a herd during episodes in which at least 2 animals showed evidence of infection; this ensured a high likelihood of exposure to M. bovis. Linear animal models, and sire and animal threshold models were used to estimate the variance components for susceptibility to M. bovis-purified protein derivative (PPD) responsiveness and confirmed M. bovis infection. The heritability estimates from the threshold sire models were biased upward because the relatedness between dam-daughter pairs was ignored. The threshold animal model produced heritability estimates of 0.14 in cows and 0.12 in heifers for susceptibility to M. bovis-PPD responsiveness, and 0.18 in cows for confirmed M. bovis infection susceptibility. Therefore, exploitable genetic variation exists among Irish dairy cows for susceptibility to M. bovis infection. Sire rankings from the linear and threshold animal models were similar, indicating that either model could be used for the analysis of susceptibility to M. bovis-PPD responsiveness. A favorable genetic correlation close to unity was observed between susceptibility to confirmed M. bovis infection and M. bovis-PPD responsiveness, indicating that direct selection for resistance to M. bovis-PPD responsiveness will indirectly reduce susceptibility to confirmed M. bovis infection. Data from the national TB eradication program could be used routinely to estimate breeding values for susceptibility to M. bovis infection.

Risk factors for visible lesions or positive laboratory tests in bovine tuberculosis reactor cattle in Northern Ireland

“…However, a similar finding was found in cattle that were classified as reactors after being subjected to the gamma interferon test (DEFRA, 2005). Other explanations include genetic/breed differences in susceptibility to bTB (Bermingham et al, 2009;Driscoll et al, 2011) and the higher within-herd transmission coefficient in dairy herds compared to non-dairy herds (Alvarez et al, 2012) There was no significant association between the number of lifetime moves or the number of animals purchased in the last three years and the VL status and bTB status of reactor animals in this study. The importance of movement and purchase of cattle as a risk factor to bTB infection has been supported by several studies (Gilbert et al, 2005;Ramirez-Villaescusa et al, 2009;Ramirez-Villaescusa et al, 2010).…”

Bovine tuberculosis: the genetic basis of host susceptibility

“…Indeed, it is only recently that effort has been directed towards quantifying the host genetic influence (Bermingham et al 2009;Brotherstone et al 2010).…”

An analysis of effects of heterozygosity in dairy cattle for bovine tuberculosis resistance

“…Previous studies have demonstrated genetic variation in resistance to bTB (Bermingham et al . 2009; Brotherstone et al . 2010) and have shown the feasibility of genomic selection for bTB resistance using information from markers dispersed throughout the genome (Tsairidou et al .…”