**1. Introduction: serum proteins**

Proteins are the main and most abundant constituents of the blood serum or plasma, having many essential physiological functions. The most of proteins present in the blood are biochemically not pure; usually, they are a mixture of simple proteins combined with other

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

substances: glycoproteins, lipoproteins, and other conjugated proteins [1]. Proteins have a specific intramolecular structure and amphoteric nature, containing the balanced portions of hydrophilic and hydrophobic groups [2]. They are macromolecules built from one or more unbranched chains of amino acids linked by peptide bonds. The chemical properties of the amino acids determine the biological activity of the protein [3].

Proteins play a central role in biological processes; some of them are involved in structural support of connective tissues, while others play important roles in biochemical reactions. Proteins also serve as buffers, helping in maintaining the acid-base balance and colloid osmotic structure. Some of them act as carriers of lipids, hormones, vitamins, and minerals in the circulatory system, and are involved in the regulation of cellular activity and immune system [4]. Other blood proteins play important roles as enzymes, complement components, or protease inhibitors. Certain blood proteins are essential for hemostasis and have important functions in platelet adhesion and aggregation, as well as coagulation [5].

Hepatocytes play the major role in the synthesis and secretion of blood proteins [6]. The major exceptions are the immunoglobulins that are produced by the immune system consisting of the reticuloendothelial tissues, lymphoid cells, activated B cells, and plasma cells in response to exposure to antigens [7, 8]. Further studies showed that nonhepatic tissues, including the intestine, lung, adipose tissue, and mammary gland, also have the capability to synthesize some serum proteins for specific functions [9, 10].

**2. Analyses of serum proteins**

to automated analysers [7].

favored its wide application in veterinary medicine.

**2.1. Chemical methods**

Blood proteins are an important indicator of health state and their evaluation represents a basis in general biochemistry [22]. The first step in the analysis of protein pattern is the quantification of total serum or plasma protein concentrations. Several methods have been developed for their determination, which are based on different analytical methods [23]. Several techniques, including chemical and physical methodologies, may be applied to analyze the concentrations of total proteins in blood and other biological fluids. Chemical methods belong to the more commonly used procedures in clinical biochemistry, since they may be to adapt

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

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**Figure 1.** Normal serum (a) and plasma (b) protein electrophoretogram in a clinically healthy cattle.

In biochemical laboratories, the most widely used analytical technique to assess the concentrations of total proteins is the biuret method. This method is based on colorimetric principle, in which the copper ions from the biuret reagent react with the amide groups from the proteins at strong alkaline pH, creating a violet color [24, 25]. However, this method is not sensitive enough to measure lower protein concentrations found, for example, in cerebrospinal fluid [26]. Despite of this disadvantage, the biuret assay is still frequently used because of simple analytical procedure, easy preparation of reagents, and when compared with other copper-based assays, this method is less susceptible to chemical interference [27]. Many of the total protein assay kits developed for the automated use in wet biochemical analyzers, as well as dry chemistry analyzers, are based on this principle. This technique is very cheap and this

The biuret method was modified by using the Folin phenol reagent (Folin-Ciocalteu), which is more sensitive and thus more appropriate to measure low concentrations of proteins [28]. In this method, the phenolic groups of tyrosine and tryptophan in proteins react with the Folin-Ciocalteu reagent producing a blue-purple colored complex [29]. The disadvantages of the Lowry method are the sensitivity to the amino acid composition of the protein and the interference with a range of substances, including buffers, drugs, and nucleic acids [30].

The protein constituents of the blood serum are qualitatively different from that of plasma, in which fibrinogen has been removed by conversion into a fibrin clot together with some other coagulation factors [11, 12]. Although serum and plasma are considered suitable samples for many chemistry tests, including serum total proteins, differences in the results obtained between these 2 sample types have been reported by some authors [13, 14]. The principal advantage of plasma over serum is the smaller amount of blood specimen that can be collected from some small animal species. In these species, heparinized plasma is the preferred sample for clinical chemistry, including protein analyses [15]. However, according to some authors, plasma and serum are not equally suitable samples for protein analyses due to noticeable differences in the electrophoretic pattern of proteins in serum and plasma. It should be taken into consideration that fibrinogen, which migrates at the end of the β region on the electrophoretogram, may influence the correct separation and identification of protein fractions [16] (**Figure 1**). Errico et al. [17] concluded also that electrophoretic analysis of proteins in plasma may provide inaccurate results unless plasma is defibrinated, caused predominantly by the possible overestimation of the β-globulin fraction.

The concentrations of proteins in serum are tightly controlled to balance their physiological functions in areas of immunity, coagulation, small molecule transport, and inflammation. Any dysfunction and out-of-balance in their concentrations can cause or result from disease processes [18]. Blood serum contains many different proteins. Some of them are present in the blood serum in concentrations higher than mg/ml, including albumin, immunoglobulins, haptoglobin, transferrin, and lipoproteins [19]. In addition to these major constituents, blood serum also contains many other proteins that are secreted by cells, and tissues in very low concentrations (measured in ng/ml or pg/ml) and in veterinary clinical biochemistry are relatively underutilized [20, 21].

**Figure 1.** Normal serum (a) and plasma (b) protein electrophoretogram in a clinically healthy cattle.
