High concentration of human lactoferrin in milk of rhLf-transgenic cows relieves signs of bovine experimental Staphylococcus chromogenes intramammary infection

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Six transgenic cows producing recombinant human lactoferrin (rhLf) in their milk and five normal cows at the same lactation stage were experimentally infected with Staphylococcus chromogenes to study the effect of a high concentration of lactoferrin in milk. Coagulase-negative staphylococci such as S. chromogenes have become very common as agents causing mild or subclinical mastitis. All transgenic cows became infected but showed no clinical signs, unlike the control cows, which developed mild clinical mastitis. Transgenic cows eliminated bacteria faster from the quarters than did the controls. Local clinical signs were milder, and the inflammatory reaction assessed by NAGase activity in the milk and by the concentration of milk amyloid A was lower in the transgenic cows. The mild response probably reflected the rapid elimination of bacteria. The milk concentration of rhLf remained constant throughout the study period, but the total concentration of bovine lactoferrin in the milk peaked in both groups at 46 h post-challenge. Three cows, all in the control group, exhibited systemic acute phase response as increased concentrations of serum amyloid A in the blood circulation. Transgenic cows with a high concentration of human lactoferrin in their milk seemed to be protected from clinical disease and from prolonged inflammatory reaction, but not from experimental intramammary infection induced by S. chromogenes.