Genetic evaluation for bovine tuberculosis resistance in dairy cattle

Abstract

Genetic evaluations for resistance to bovine tuberculosis (bTB) were calculated based on British national data including individual animal tuberculin skin test results, postmortem examination (presence of bTB lesions and bacteriological culture for Mycobacterium bovis), animal movement and location information, production history, and pedigree records. Holstein cows with identified sires in herds with bTB breakdowns (new herd incidents) occurring between the years 2000 and 2014 were considered. In the first instance, cows with a positive reaction to the skin test and a positive postmortem examination were defined as infected. Values of 0 and 1 were assigned to healthy and infected animal records, respectively. Data were analyzed with mixed models. Linear and logit function heritability estimates were 0.092 and 0.172, respectively. In subsequent analyses, breakdowns were split into 2-mo intervals to better model time of exposure and infection in the contemporary group. Intervals with at least one infected individual were retained and multiple intervals within the same breakdown were included. Healthy animal records were assigned values of 0, and infected records a value of 1 in the interval of infection and values reflecting a diminishing probability of infection in the preceding intervals. Heritability and repeatability estimates were 0.115 and 0.699, respectively. Reliabilities and across time stability of the genetic evaluation were improved with the interval model. Subsequently, 2 more definitions of "infected" were analyzed with the interval model: (1) all positive skin test reactors regardless of postmortem examination, and (2) all positive skin test reactors plus nonreactors with positive postmortem examination. Estimated heritability was 0.085 and 0.089, respectively; corresponding repeatability estimates were 0.701 and 0.697. Genetic evaluation reliabilities and across time stability did not change. Correlations of genetic evaluations for bTB with other traits in the current breeding goal were mostly not different from zero. Correlation with the UK Profitable Lifetime Index was moderate, significant, and favorable. Results demonstrated the feasibility of a national genetic evaluation for bTB resistance. Selection for enhanced resistance will have a positive effect on profitability and no antagonistic effects on current breeding goal traits. Official genetic evaluations are now based on the interval model and the last bTB trait definition.

Genomic regions underlying susceptibility to bovine tuberculosis in Holstein-Friesian cattle

“…Data for the present study were sire genetic evaluations that had been previously generated from the official genetic and genomic evaluation system for bTB resistance [15, 22]. These genetic evaluations had been based on skin test and post-mortem examination records of Holstein-Friesian cows obtained from breakdowns (herds with bTB incidents) that occurred between the years 2000 and 2014.…”

“…either infected (case) or healthy (control). Three alternative definitions of “infected” from Banos et al [15] were considered:Phenotype 1: positive reactors to the skin test with positive post-mortem examination results consisting of visible lesions of bTB and/or positive M. bovis culture. This phenotype represented the conservative definition of infected, which requires infection to be confirmed by post-mortem examination.…”

“…Each sire received three EBVs, one for each of the above trait definitions. More information about the genetic model used to derive these sire EBVs may be found in Banos et al [15]. In the current study, sire EBVs were deregressed and used as phenotypes.…”

“…Each bTB trait was analysed separately. Prior to the association analyses, deregressed EBVs were weighted using the formula outlined by Garrick et al [24]:where ω i is the weighting factor of the deregressed EBV of the i th animal; h 2 is the heritability of the trait (h 2  = 0.09 [15]); r i 2 is the reliability of the deregressed EBV of the i th sire and c is the genetic variance not accounted for by the SNPs. A value of 0.20 [27] was considered for c.…”

Продуктивное Долголетие Коров Голштинской Породы Европейской Селекции В Условиях Промышленной Технологии

“…Однако коммерциализация молочного скота сопровождается и рядом негативных последствий: ухудшением качества молока, снижением иммунного статуса животных, плодовитости, сокращением периода хозяйственного использования коров в стадах (Goncharenko, 2016;Denholm, et al, 2017;Charfeddine & Pérez-Cabal, 2016). Авторы (Donnik et al, 2010;Weber et al, 2013;Compton et al, 2016;De Vries, 2017) сообщают о том, что короткая длительность хозяйственного использования у высокопродуктивных коров связанна с более высокими обменными процессами в их организме, поскольку в сложных условиях они более склоны к заболеваниям и нарушениям репродуктивной функции, чем животные со средними показателями продуктивности, не исключая при этом влияния генетических факторов (Abdalla et al, 2016;VandeHaar et al, 2016;Tsuruta et al, 2017;Banos et al, 2017). Сокращение сроков продуктивного использования животных в условиях промышленной технологии должно послужить стимулом для глубокого изучения и поиска путей решения этой проблемы.…”