Abstract
BackgroundIn dairy herds, mastitis causes detrimental economic losses. Genetic selection offers a sustainable tool to select animals with reduced susceptibility towards postpartum diseases. Studying underlying mechanisms is important to assess the physiological processes that cause differences between selected haplotypes. Therefore, the objective of this study was to establish an in vivo infection model to study the impact of selecting for alternative paternal haplotypes in a particular genomic region on cattle chromosome 18 for mastitis susceptibility under defined conditions in uniparous dairy cows.ResultsAt the start of pathogen challenge, no significant differences between the favorable (Q) and unfavorable (q) haplotypes were detected. Intramammary infection (IMI) with Staphylococcus aureus 1027 (S. aureus, n = 24, 96 h) or Escherichia coli 1303 (E. coli, n = 12, 24 h) was successfully induced in all uniparous cows. This finding was confirmed by clinical signs of mastitis and repeated recovery of the respective pathogen from milk samples of challenged quarters in each animal. After S. aureus challenge, Q-uniparous cows showed lower somatic cell counts 24 h and 36 h after challenge (P < 0.05), lower bacterial shedding in milk 12 h after challenge (P < 0.01) and a minor decrease in total milk yield 12 h and 24 h after challenge (P < 0.01) compared to q-uniparous cows.ConclusionAn in vivo infection model to study the impact of genetic selection for mastitis susceptibility under defined conditions in uniparous dairy cows was successfully established and revealed significant differences between the two genetically selected haplotype groups. This result might explain their differences in susceptibility towards IMI. These clinical findings form the basis for further in-depth molecular analysis to clarify the underlying genetic mechanisms for mastitis resistance.
Highlights
In dairy herds, mastitis causes detrimental economic losses
The success of intramammary infection was confirmed by clinical signs of mastitis: changes in milk secretion and udder firmness were observed after challenge with both pathogens (Tables 1 and 2)
At the start of the experiment, no significant differences regarding udder-specific parameters were found between the two haplotypes, Quniparous cows had shown a lower incidence of metritis, lower blood concentrations of betahydroxbutyrate compared to q-uniparous cows, numerical lower incidence of Clinical mastitis (CM) and subclinical mastitis (SCM) in the postpartum period and significant differences in somatic cell count (SCC) as recently published [37,38,39]
Summary
The objective of this study was to establish an in vivo infection model to study the impact of selecting for alternative paternal haplotypes in a particular genomic region on cattle chromosome 18 for mastitis susceptibility under defined conditions in uniparous dairy cows. Mastitis has caused large-scale economic losses worldwide in dairy farming due to treatment costs, discarded milk, reduced milk yield and increased culling rates [1,2,3,4,5,6]. Dollars per milking cow per year, in which nearly half of the costs were associated with subclinical mastitis [7]. Indirect costs arise due to reduced fertility of cows suffering from clinical or subclinical mastitis [8,9,10].
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