title: Milk prolactin response and quarter milk yield after experimental infection with coagulase-negative staphylococci in dairy heifers.
abstract: Coagulase-negative staphylococci (CNS) are the most common bacteria involved in subclinical mastitis in dairy cows. Remarkably, CNS-infected dairy heifers produce more milk than uninfected heifers. Because the lactation hormone prolactin (PRL) is also involved in mammary gland immunity, we investigated the milk PRL response and the mammary quarter milk yield following experimental CNS challenge. Eight healthy Holstein-Friesian heifers in mid-lactation were experimentally infected using a split-udder design with 3 different CNS strains: one Staphylococcus fleurettii (from sawdust bedding) and 2 Staphylococcus chromogenes strains (one isolate from a teat apex, the other isolate from a chronic intramammary infection). Three mammary quarters per heifer were simultaneously inoculated with 1.0×10(6) cfu, whereas the remaining mammary quarter was infused with sterile phosphate-buffered saline, serving as a control. An existing radioimmunoassay was modified, validated, and used to measure PRL frozen-thawed milk at various time points until 78h after challenge. The mean milk PRL level tended to be higher in the CNS-challenged mammary quarters compared with the control mammary quarters (7.56 and 6.85ng/mL, respectively). The increase in PRL over time was significantly greater in the CNS-challenged mammary quarters than in the control mammary quarters. However, no difference was found in the PRL response when comparing each individual CNS strain with the control mammary quarters. The mean mammary quarter milk yield tended to be lower in the CNS-infected mammary quarters than in the control mammary quarters (1.73 and 1.98kg per milking, respectively). The greatest milk loss occurred in the mammary quarters challenged with the intramammary strain of S. chromogenes. Future observational studies are needed to elucidate the relation between PRL, the milk yield, and the inflammatory condition, or infection status, of the mammary gland.
authors.affiliation: M-team and Mastitis and Milk Quality Research Unit, Department of Reproduction, Obstetrics and Herd Health, Faculty of Veterinary Medicine, Ghent University, 9820 Merelbeke, Belgium. Electronic address: Kristine.Piccart@UGent.be.
authors.forename: K
authors.initials: K
authors.lastname: Piccart
authors.affiliation: M-team and Mastitis and Milk Quality Research Unit, Department of Reproduction, Obstetrics and Herd Health, Faculty of Veterinary Medicine, Ghent University, 9820 Merelbeke, Belgium.
authors.forename: S
authors.initials: S
authors.lastname: Piepers
authors.affiliation: M-team and Mastitis and Milk Quality Research Unit, Department of Reproduction, Obstetrics and Herd Health, Faculty of Veterinary Medicine, Ghent University, 9820 Merelbeke, Belgium.
authors.forename: J
authors.initials: J
authors.lastname: Verbeke
authors.affiliation: Laboratory of Animal Endocrinology and Reproduction, Faculty of Veterinary Medicine, University of Liege, 4000 Liege, Belgium.
authors.forename: N M
authors.initials: NM
authors.lastname: de Sousa
authors.affiliation: Laboratory of Animal Endocrinology and Reproduction, Faculty of Veterinary Medicine, University of Liege, 4000 Liege, Belgium.
authors.forename: J F
authors.initials: JF
authors.lastname: Beckers
authors.affiliation: M-team and Mastitis and Milk Quality Research Unit, Department of Reproduction, Obstetrics and Herd Health, Faculty of Veterinary Medicine, Ghent University, 9820 Merelbeke, Belgium.
authors.forename: S
authors.initials: S
authors.lastname: De Vliegher
mesh_terms: D000818:Animals; D002417:Cattle; D004195:Disease Models, Animal; D005260:Female; D007774:Lactation; D008321:Mammary Glands, Animal / Q000382:microbiology; D008414:Mastitis, Bovine / Q000382:microbiology; D008892:Milk / Q000378:metabolism*; D011388:Prolactin / Q000378:metabolism*; D013203:Staphylococcal Infections / Q000662:veterinary*; D013210:Staphylococcus / Q000254:growth & development* / Q000302:isolation & purification
chemical_list: D011388:Prolactin
keywords: coagulase-negative staphylococci; dairy heifer; experimental mastitis; prolactin