Variance components for susceptibility to Mycobacterium bovis infection in dairy and beef cattle

Abstract

Open Access Research Variance components for susceptibility to Mycobacterium bovis infection in dairy and beef cattle

Ian W Richardson12, Dan G Bradley1, Isabella M Higgins3, Simon J More3, Jennifer McClure4 and Donagh P Berry2*

* Corresponding author: Donagh P Berry Donagh.berry@teagasc.ie

Author Affiliations

1 Smurfit Institute of Genetics, University of Dublin, Trinity College, Dublin, Ireland

2 Animal and Grassland Research and Innovation Center, Teagasc, Moorepark, Fermoy, Co. Cork, Ireland

3 UCD Centre for Veterinary Epidemiology and Risk Analysis, UCD School of Veterinary Medicine, University College Dublin, Belfield, Dublin 4, Ireland

4 Irish Cattle Breeding Federation, Bandon Co. Cork, Ireland

For all author emails, please log on.

Genetics Selection Evolution 2014, 46:77 doi:10.1186/s12711-014-0077-1

The electronic version of this article is the complete one and can be found online at: http://www.gsejournal.org/content/46/1/77

Received: 28 November 2013 Accepted: 29 October 2014 Published: 18 November 2014

© 2014 Richardson et al.; licensee BioMed Central Ltd.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Formula display: Abstract Background

Infection of livestock with bovine tuberculosis (bTB; Mycobacterium bovis) is of major economical concern in many countries; approximately 15 000 to 20 000 cattle are infected per year in Ireland. The objective of this study was to quantify the genetic variation for bTB susceptibility in Irish dairy and beef cattle. Methods

A total of 105 914 cow, 56 904 heifer and 21 872 steer single intra-dermal comparative tuberculin test records (i.e., binary trait) collected from the years 2001 to 2010 from dairy and beef herds were included in the analysis. Only animal level data pertaining to periods of herd bTB infection were retained. Variance components for bTB were estimated using animal linear and threshold mixed models and co-variances were estimated using sire linear mixed models. Results

Using a linear model, the heritability for susceptibility to bTB in the entire dataset was 0.11 and ranged from 0.08 (heifers in dairy herds) to 0.19 (heifers in beef herds) among the sub-populations investigated. Differences in susceptibility to bTB between breeds were clearly evident. Estimates of genetic correlations for bTB susceptibility between animal types (i.e., cows, heifers, steers) were all positive (0.10 to 0.64), yet different from one. Furthermore, genetic correlations for bTB susceptibility between environments that differed in herd prevalence of bTB ranged from 0.06 to 0.86 and were all different from one. Conclusions

Genetic trends for bTB susceptibility observed in this study suggest a slight increase in genetic susceptibility to bTB in recent years. Since bTB is of economic importance and because all animals are routinely tested at least once annually in Ireland and some other countries, the presence of genetic variation for bTB susceptibility suggests that bTB susceptibility should be included in a national breeding program to halt possible deterioration in genetic susceptibility to bTB infection.