Genetics of mastitis in dairy ruminants.

Abstract

Mastitis is a multifactorial infectious disease, mainly caused by bacteria that infect the mammary gland. It is one of the major diseases in dairy ruminants, with respect to industry and public concern, economic impact, zoonotic potential and animal welfare. Genetic control of mastitis has been widely demonstrated. Accordingly, most countries have developed breeding programmes to improve udder health. Most evidence for host genetic variability, and its application for genetic improvement, is principally based on a few basic phenotypic traits related to healthy versus diseased status such as milk somatic cell counts (SCC) and clinical mastitis (CM) occurrence. Additionally, considerable progress has been made in the last decade to scrutinize immune mechanisms and genes that play key roles in the mammary gland defences. Accumulating QTL detection studies have allowed localization of regions of the genome that explain a large part of genetic variability for either SCS or CM traits on almost all autosomal chromosomes. However, resistance to mastitis is a highly complex trait, the genetically determined biological basis of which is mostly unknown. There is still an open field for development of additional relevant phenotypes that can be routinely collected. Further, additional studies are necessary to better understand the genetic basis of mastitis resistance, to predict long-term responses to selection and to develop new tools and strategies for genetic improvement of udder health.

Immune response from a resource allocation perspective

“…Clinical mastitis cases are principally associated with one of the following bacteria: S. Aureus, E. Coli, Streptococcus dysgalactiae, Streptococcus uberis, CNS, Arcanobacterium pyogenes , or Klebsiella spp (Rupp and Foucras, 2010). The genetic antagonism between milk yield and mastitis resistance has been well established (Rupp and Boichard, 2003).…”

Response of the goat mammary gland to infection with Staphylococcus aureus revealed by gene expression profiling in milk somatic and white blood cells

“…However, it is not certain how well SCS predicts immune response to infection with a mastitis causing pathogens, or incidence of clinical mastitis. Nevertheless, breeding programmes for mastitis resistance in dairy cattle [14,15] and sheep [16] have used SCS as a selection criterion. For goats, the relevance of SCS as a predictor of parameters of udder health and the susceptibility against mastitis is still untested.…”

Association of subclinical mastitis prevalence with sheep breeds in Greece

“…However, it is difficult to implement at a large scale and also has various limitations. Moreover, bacterial shedding is variable and levels may sometimes be too low to be detected by conventional techniques (Rupp & Foucras, 2010). Simple, indirect methods have also been widely applied, based on evaluation of inflammation.…”

“…Traditional Greek sheep breeds have shown reduced frequency of subclinical mastitis. In a broader sense, resistance could be defined as the ability to avoid any infection and/or the quick recovery from an infection (Rupp & Boichard, 2003) and involves different components: avoiding entry of the pathogen into the teat, mounting an immune response capable of limiting its development in the mammary gland and clearing the infection, as well as controlling the pathogenic effects of the infection, such as tissue damage (Rupp & Foucras, 2010). In Karagouniko ewes, lymphoid follicles have been identified in the teat duct and have been repeatedly shown to play a clear protective role against invading pathogens (Fragkou et al 2010).…”

“…In addition, udders with bad conformation can predispose to development of mastitis (Gelasakis et al 2012). Further, differences in somatic cell counts in milk of healthy animals recorded between sheep breeds (Rupp & Foucras, 2010) can reflect the immunological competence of the respective mammary glands against invading microorganisms and the final result (Albenzio et al 2012).…”