Proceedings of the World Congress on Genetics Applied to Livestock Production, 11.529 ChronMast - a model to study functional genetic variation of mastitis susceptibility Biologically informed breeding requires detailed knowledge on the genomic variants modulating the target phenotype as well as on the potential (patho)physiological consequences of those variants. In dairy cattle, mastitis is one of the most frequent and costly diseases. However, there is limited progress in elucidating the genomic and physiological background of its genetic variation. Based on a previously established animal model and on further data from the literature, we set up an experimental design with halfsib ships of heifers inheriting alternative paternal haplotypes on a target interval on Bos taurus chromosome 18 (BTA18). Sires were selected for highly divergent SNP effects of the alternative haplotypes for somatic cell score, a surrogate trait for mastitis incidence, and heifers were assigned to experimental groups according to their inheritance of either the favourable (GQ) or unfavourable (kq) paternal haplotype. The animals were allocated six weeks prior to first calving as either long-term cell donors (LT) until day 42 of the second lactation (n=6) or for experimental challenge with mastitis pathogens (E. coli, S. aureus) (IC) at day 36 ± 3.4 of the first lactation (n=36). Significantly more kq animals compared to GQ individuals were diagnosed with one or more infectious diseases (P<0.05) between parturition and the start of the mastitis challenge at about five weeks after calving. Furthermore, during the course of lactation the kq animals of the long-term group displayed significantly higher somatic cell score compared to GQ. Interestingly, in the first six weeks after calving the proportion of quarters with extremely low somatic cell count (< 10,000 cells/ml) was significantly higher in both kq groups (LT, IC) compared to their GQ counterparts (P < 0.01, P < 0.05, respectively). The differences in disease incidence and in somatic cell score particularly during the second stage of lactation indicate that indeed the groups GQ and kq comprise animals of divergent susceptibility for infectious diseases. The mastitis challenge experiment and comprehensive subsequent immunological, endocrinological, immunohistochemical and transcriptomic analyses will reveal potential differences concerning the response towards the intramammary infection. These differences will provide knowledge on the (patho)physiological background of divergent mastitis susceptibility and will aid the detection of the underlying genetic variation. Keywords: mastitis, somatic cell count, challenge, animal model

Marie Meyerholz, Annika Heimes, Johanna Brodhagen, Laura Rohmeier, Tordis Eickhoff, Sebastian Jander, Alina Huelsebusch, Rosemarie Weikard, Juliane Günther, Hans-Martin Seyfert, Holm Zerbe, Wolfram Petzl, Martina Hoedemaker, Hans-Joachim Schuberth, Susanne Engelmann, Christa Kuehn

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume Biology - Disease Resistance 1, , 529, 2018
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