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Abstract/Summary
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<jats:title>Abstract</jats:title><jats:sec>
<jats:title>Background</jats:title>
<jats:p>In dairy cattle, mastitis causes high financial losses and impairs animal well-being. Genetic selection is used to breed cows with reduced mastitis susceptibility. Techniques such as milk cell flow cytometry may improve early mastitis diagnosis. In a highly standardized in vivo infection model, 36 half-sib cows were selected for divergent paternal <jats:italic>Bos taurus</jats:italic> chromosome 18 haplotypes (Q <jats:italic>vs</jats:italic>. q) and challenged with <jats:italic>Escherichia coli</jats:italic> for 24 h or <jats:italic>Staphylococcus aureus</jats:italic> for 96 h, after which the samples were analyzed at 12 h intervals. Vaginal temperature (VT) was recorded every three minutes. The objective of this study was to compare the differential milk cell count (DMCC), milk parameters (fat %, protein %, lactose %, pH) and VT between favorable (Q) and unfavorable (q) haplotype cows using Bayesian models to evaluate their potential as improved early indicators of differential susceptibility to mastitis.</jats:p>
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<jats:title>Results</jats:title>
<jats:p>After <jats:italic>S. aureus</jats:italic> challenge, compared to the Q half-sibship cows, the milk of the q cows exhibited higher PMN levels according to the DMCC (24 h, <jats:italic>p</jats:italic> < 0.001), a higher SCC (24 h, <jats:italic>p</jats:italic> < 0.01 and 36 h, <jats:italic>p</jats:italic> < 0.05), large cells (24 h, <jats:italic>p</jats:italic> < 0.05) and more dead (36 h, <jats:italic>p</jats:italic> < 0.001) and live cells (24 h, <jats:italic>p</jats:italic> < 0.01). The protein % was greater in Q milk than in q milk at 0 h (<jats:italic>p</jats:italic> = 0.025). In the <jats:italic>S. aureus</jats:italic> group, Q cows had a greater protein % (60 h<jats:italic>, p</jats:italic> = 0.048) and fat % (84 h, <jats:italic>p</jats:italic> = 0.022) than q cows. Initially, the greater VT of <jats:italic>S. aureus</jats:italic>-challenged q cows (0 and 12–24 h, <jats:italic>p</jats:italic> < 0.05) reversed to a lower VT in q cows than in Q cows (48–60 h, <jats:italic>p</jats:italic> < 0.05).</jats:p>
<jats:p>Additionally, the following findings emphasized the validity of the model: in the <jats:italic>S. aureus</jats:italic> group all DMCC subpopulations (24 h-96 h, <jats:italic>p</jats:italic> < 0.001) and in the <jats:italic>E. coli</jats:italic> group nearly all DMCC subpopulations (12 h-24 h, <jats:italic>p</jats:italic> < 0.001) were higher in challenged quarters than in unchallenged quarters. The lactose % was lower in the milk samples of <jats:italic>E. coli</jats:italic>-challenged quarters than in those of <jats:italic>S. aureus</jats:italic>-challenged quarters (24 h, <jats:italic>p</jats:italic> < 0.001). Between 12 and 18 h, the VT was greater in cows challenged with <jats:italic>E. coli</jats:italic> than in those challenged with <jats:italic>S. aureus</jats:italic> (3-h interval approach, <jats:italic>p</jats:italic> < 0.001).</jats:p>
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<jats:title>Conclusion</jats:title>
<jats:p>This in vivo infection model confirmed specific differences between Q and q cows with respect to the DMCC, milk component analysis results and VT results after <jats:italic>S. aureus</jats:italic> inoculation but not after <jats:italic>E. coli</jats:italic> challenge. However, compared with conventional milk cell analysis monitoring, e.g., the global SCC, the DMCC analysis did not provide refined phenotyping of the pathogen response.</jats:p>
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