*4.3.1.6. Ceruloplasmin*

Ceruloplasmin (Cp) is a ferroxidase enzyme that is the major copper-carrying protein in the blood, and plays a role in iron metabolism [183]. Ceruloplasmin carries 70–95% of the total copper in plasma, and thus might play a role in Cu and iron homeostasis [184]. Furthermore, ceruloplasmin is involved in cellular prooxidant and antioxidant processes, and has antibacterial activities [185]. It is produced by the liver as apoceruloplasmin, an unstable non-copper-bound form, which subsequently reacts with seven copper atoms forming holoceruloplasmin, a functional and more stable product [186].

Ceruloplasmin has been evaluated as a marker of animal health and welfare [187]. Several studies in cattle indicate its diagnostic use with applications in many disease conditions, including uterine bacterial contamination, as well as clinical and subclinical mastitis [177, 188]. Hussein et al. [189] evaluated ceruloplasmin activity in dairy cows in different lactation stages, showing higher values in fresh-lactation stage. López-Alonso et al. [190] measured ceruloplasmin as a potential marker of hepatic copper accumulation in cattle. Studies in young animals have shown that the concentrations of ceruloplasmin in the serum increases during induced pneumonic pasteurellosis, with the highest concentration observed 2 and 4 hours after the inoculation [191].

*4.3.2.2. Lactoferrin*

and fungi [203].

than during lactation [207, 208].

*4.3.2.3. C-reactive protein*

Lactoferrin (Lf), also known as lactotransferrin, is a multifunctional protein of the transferrin proteins capable of binding and transferring Fe3\* ions. Lactoferrin is a globular glycoprotein with a molecular weight of about 80 kDa, which shows high affinity for iron [196]. Although the overall structure of lactoferrin is very similar to that of transferrin, they differ in their relative affinities for Fe and the propensity for release of Fe [197]. The capability of lactoferrin to bind iron is two times higher than that of transferrin [198]. This bound is very strong and can resist pH values of as low as 4 [199]. The ability to keep iron bound even at low pH is important, especially at sites of infection and inflammation where, due to metabolic activity of bacteria, the pH may fall under 4.5 [200]. The most of bacterial pathogens necessitate Fe for metabolic activities, growth, and proliferation. Since lactoferrin has Fe-binding capacity, it reduces the growth of Fe-requiring pathogenic bacteria including enteropathogenic *E. coli* [201]. Lactoferrin is a major component of the innate immune system of mammalians and represents one of the first defense systems against microbial agents, which invaded the organism mostly by mucosal tissues [202]. It affects the growth and proliferation of many infectious agents including both Gram-positive and Gram-negative bacteria, viruses, protozoa,

The Use of Serum Proteins in the Laboratory Diagnosis of Health Disorders in Ruminants

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Lactoferrin is expressed in most biological fluids, including milk, saliva, and nasal secretions. It is present in blood, plasma, or serum in relatively low concentrations, but its concentrations increase during infection, inflammation, excessive intake of iron, or tumor growth [204]. Higher concentrations of lactoferrin were observed in bovine and human milk, or colostrum. The lactoferrin values in milk of healthy cows are quite variable and may range from 1.15 to 485.63 μg/ml. On the other hand, sub-clinical and clinical mastitis may lead to rapid increase of its concentrations positively correlating with SCC, stage of lactation, and milk yield [205, 206]. The concentrations of lactoferrin are higher in colostrum (varying between 1 and 5 mg/ml), during drying-off and early mammary involution period

Lactoferrin plays a key role in the defense mechanisms of the mammary gland, contributing to the prevention of microbiological infection diseases [209]. Therefore, the concentrations of lactoferrin in milk are markedly influenced by the health status of the cows. Harmon et al. [210] induced *E. coli* infection in bovine mammary gland. In these cows, they found a 30-fold increase of lactoferrin values in the mammary secretion 90 h after the inoculation. Furthermore, they concluded that acute mastitis is associated with 30-fold increase of the concentrations of lactoferrin in the milk with the greatest production in the infected quarter.

C-reactive protein (CRP) was the first identified acute-phase protein, which was named according to its ability to bind to C-polysaccharide of Gram-positive bacteria [211]. It is a non-glycosylated protein from the group of pentraxins, and is composed of 5 subunits that firmly bind to C-polysaccharides [212]. Following bacterial infection, CRP binds to pathogen and activates the classical complement pathway leading to the opsonization of the bacteria
