Abstract #T277

# T277
Intravenous challenge with lipopolysaccharide does not induce a mammary immune response in dairy cows and does not affect the blood-milk barrier.
Olga Wellnitz*1,2, Emmanouil Kalaitzakis1,2, Heinrich Bollwein2, Rupert M. Bruckmaier1, 1Veterinary Physiology, Vetsuisse Faculty University of Bern, Bern, Switzerland, 2Clinic of Reproductive Medicine, Vetsuisse Faculty University of Zurich, Zurich Switzerland.

An intramammary challenge with lipopolysaccharide (LPS) from Escherichia coli is known to induce a considerable immune response of the mammary gland and an impairment of the blood-milk barrier. The aim of the current study was to investigate a potential immune reaction in the mammary gland and potential changes of the integrity of the blood-milk barrier in response to an intravenous, i.e., systemic challenge, with LPS. Ten lactating dairy cows in wk 3 of lactation were challenged intravenously (V. jugularis) with 0.5 µg/kg BW E. coli LPS (O26:B6). Rectal temperature was measured hourly. Milk samples of one udder quarter were taken immediately before and then every 30 min until 5 h after challenge. Mammary gland biopsies of one quarter were taken immediately before and 8 h after LPS challenge for RT-qPCR of immunorelevant factors. Rectal temperature increased (P < 0.001) within 1 h of LPS administration from 38.3 ± 0.1 to 39.2 ± 0.1°C and stayed elevated throughout the 5 h of experiment. The milk somatic cell count was 83.3 ± 19.1 × 103/mL immediately before challenge and did not change throughout the experiment. Lactate-dehydrogenase concentrations in milk as a marker for blood-milk barrier impairment was 48.1 ± 6.0 U/L immediately before challenge and did not change throughout the experiment. Relative mRNA expression of immunorelevant factors; that is, the cytokines TNF-α and interleukin-1β in mammary gland tissue did not change in response to intravenous LPS injection. In conclusion, in contrast to intramammary injections, an intravenous injection of 0.5 µg/kg BW LPS induces a systemic immune response shown by an increase in rectal temperature, but has obviously no effects on factors of mammary gland immune response which typically change during LPS-induced mastitis. Also the blood-milk barrier integrity does not appear to be influenced by systemic LPS.

Key Words: intravenous lipopolysaccharide, mammary gland, blood-milk barrier