This is the first study describing an experimental
mastitis model using transgenic cows expressing recombinant human
lactoferrin (rhLf) in their milk. The aim of the study was to investigate the concentrations in milk and protective effects of bovine and recombinant human
lactoferrin in experimental Escherichia coli
mastitis. Experimental intramammary
infection was induced in one udder quarter of seven first-lactating rhLf-transgenic cows and six normal cows, using an E. coli strain isolated from cows with clinical
mastitis and known to be susceptible to Lf in vitro. Clinical signs were recorded during the experimental period, concentrations of human and bovine Lf and indicators of
inflammation and bacterial counts were determined for milk, and concentrations of
acute-phase proteins and
tumor necrosis factor alpha were determined for sera and milk. Serum
cortisol and blood hematological and biochemical parameters were also determined. Expression levels of rhLf in the milk of transgenic cows remained constant throughout the experiment (mean, 2.9 mg/ml). The high Lf concentrations in the milk of transgenic cows did not protect them from intramammary
infection. All cows became infected and developed clinical
mastitis. The rhLf-transgenic cows showed milder systemic signs and lower serum
cortisol and
haptoglobin concentrations than did controls. This may be explained by
lipopolysaccharide-neutralizing and immunomodulatory effects of the high Lf concentrations in their milk. However, Lf does not seem to be a very efficient
protein for genetic engineering to enhance the
mastitis resistance of dairy cows.