Development of national genetic evaluations of beef cattle for resistance to bovine tuberculosis (bTB)

Project Number:               61100033

Lead Contractor:              SAC Commercial LTD

Start & end dates:             01 November 2017– 31 October 2019

 

The Problem:

Bovine tuberculosis (bTB) is a zoonotic disease endemic in the UK and other countries, and presents a significant challenge to the UK cattle sector. The Department for Environment, Food and Rural Affairs (DEFRA) lists bTB as one of the four most important livestock diseases globally, incurring annual costs of about £175 million in the UK.

Recent research conducted by the project team has led to the development of the first national genetic and genomic evaluation for bTB resistance in dairy breeds and the launch of TB Advantage by AHDB. The research confirmed the existence of significant genetic variation among individual animals for resistance to bTB infection, mainly inferred from the intradermal (skin) test and the presence of lesions and bacteriological tests following slaughter. Building on this know-how and experience, this project is aimed at the development of a national genetic evaluation for bTB resistance in beef cattle.

 

Aims and Objectives:

The overall aim of the project is to develop a system for routine national genetic evaluations of beef cattle for bTB resistance. In order to achieve the goal the project team will:

  1. Develop a national database for the genetic evaluation based on bTB surveillance and pedigree records of beef cattle, combining data from the Animal and Plant Health Agency of DEFRA, the British Cattle Movement Service, individual breed societies, BASCO and the Edinburgh Genetic Evaluation Services
  2. Define bTB resistance phenotypes for individual animals based on their health status; the latter will be defined from skin test results and post-mortem examination records
  3. Estimate genetic parameters for bTB resistance in beef cattle using the phenotypes from step (2) after building and assessing relevant statistical models of analysis
  4. Estimate breeding values (EBV) of individual animals for bTB resistance based on phenotypes from step (2) and genetic parameters from step (3)
  5. Estimate the correlation of bTB EBVs with genetic evaluations for other traits in the breeding goal to assess the impact of selecting for enhanced resistance on beef traits
  6. Develop genomic predictions and evaluations for bTB resistance based on results from step (4) and a validation process
  7. Integrate all results into a system for routine genetic evaluations ensuring full automation of the process and including safeguards for the quality of the outcome

 

Approach:

The existing system of combining bovine Tuberculosis (bTB) surveillance records from the Animal and Plant Health Agency (APHA) with data from the British Cattle Movement Service (BCMS), breed societies and EGENES will be used to develop a national bTB database for beef cattle genetic evaluations (Objective 1). The APHA data include intradermal (skin) test records and dates, and results of post-mortem examination for visible lesions and culture for the Mycobacterium bovis (the bTB pathogen). All beef breeds available in the APHA database will be considered in this project. The BCMS data will complement those from APHA in identifying healthy contemporaries to positive skin test reactors prior to 2011 (i.e. the period when non-reactors were not recorded in the surveillance data). Pedigree data from EGENES and the breed societies will provide information on the animals’ date of birth, sire and dam, and also the percentage of each breed. The latter will be used to estimate levels of heterosis and recombination in the crosses, which will be needed for the genetic evaluation.

The health status of each animal with regards to bTB will be determined based on results of the skin test and post-mortem examination; the method has been previously applied on dairy data and is described in detail by Banos et al. (2016, J Dairy Sci). The derived health status will constitute the animal’s phenotype regarding resistance to bTB

From these data genetic parameter estimates of the trait will be determined.  Genetic evaluations (estimated breeding values – EBVs) will then be calculated for each animal based on these genetic parameters.  These steps, together with further analysis, will be integrated into a routine genetic evaluation system. The process will be fully automated and monitored throughout with regular quality assurance checks.