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Hematological and immunological development from birth to six months of age in Holstein calves

Desenvolvimento hematológico e imunológico em bezerros Holandeses do nascimento aos seis meses de idade

ABSTRACT

The hematological and immunological development of calves from birth to 6 months of age was performed by hemogram and cellular phenotype. Ten male Holstein calves were assessed in 13 moments: before colostrum intake (D0), every 2 days until the 10th day of life (D2 to D10), at the 15th day after birth (D15), and then monthly up to 6 months (D180). Calves presented hemoconcentration on day (D) 0 and showed a gradual decrease in hematimetric rates until D180. The inversion of the neutrophilic for lymphocytic profile was observed on D4. The percentage of CD3+ cells on D10 was higher than D30 up to D180. The number of CD4+ and CD8+ cells did not change between time points. The number of CD21+ lymphocytes was significantly higher at early time points of D0 up to D15, compared on D30 until D150. In conclusion, the neonatal period was marked by stress leukogram in the first 4 days, and low number of B lymphocytes. These might be risk factors for bacterial infections responsible for navel inflammation and diarrhea. The increase in the number of B cells from 30 days of age demonstrated that the calves were functional and able to generate an immune response.

Keywords:
bovine; immune system; leukogram; immunophenotyping; flow cytometry

RESUMO

O desenvolvimento hematológico e o imunológico de bezerros do nascimento aos seis meses de idade foram avaliados por meio hemograma e imunofenotipagem dos linfócitos. Para tanto, 10 bezerros machos Holandeses foram avaliados em 13 momentos: antes da ingestão do colostro (D0), a cada dois dias até o 10º dia (D2 a D10), 15º dia (D15) e, em seguida, mensalmente até seis meses de idade (D180). Os bezerros apresentaram hemoconcentração em D0 e decréscimo gradual dos índices hematimétricos até D180. A inversão do perfil neutrofílico para linfocítico foi observada em D4. Os valores de CD3+ (%) em D10 foram maiores que aqueles observados em D30 até D180. CD4+ e CD8+ não apresentaram alterações entre os momentos. Os linfócitos B CD21+ aumentaram significativamente a partir dos primeiros momentos D0 até D15, em comparação com os momentos subsequentes D30 até D150. Em conclusão, o período neonatal foi caracterizado pelo leucograma de estresse nos primeiros quatro dias e o baixo número de linfócitos B. Esses fatos podem ser considerados como fatores de risco para infecções bacterianas responsáveis pelas inflamações umbilicais e pela diarreia. Por outro lado, o aumento de células B após os 30 dias de vida demonstrou que os bezerros foram capazes de gerar uma resposta imune.

Palavras-chave:
bovino; sistema imune; leucograma; imunofenotipagem; citometria de fluxo

INTRODUCTION

Newborn calves are considered immune-naïve and agammaglobulinemic at birth, because of the synepitheliochorial placenta from dams, which prevents the passage of pathogens to the fetus during pregnancy. Even though this barrier maintains the sterility of the placental environment, it is also associated with two negative consequences for the neonate: agammaglobulinemia and absence of an immunological memory at birth (Barrington and Parrish, 2001BARRINGTON, G.M.; PARISH, S.M. Bovine neonatal immunology. Vet. Clin. N. Am. Food Anim. Pract., v.17, p.463-476, 2001.).

Progesterone, prostaglandins, and the cytokines interleukin (IL)-4 and IL-10, produced by the placenta during pregnancy, are responsible for the suppression of the Th1 maternal response, which releases toxic cytokines for the fetal-placental environment. The predominance of the Th2 immune response is responsible for the susceptibility of the newborn to intracellular pathogens (Wegmannet al., 1993WEGMANN, T.G.; LIN, H.; GUILBERT, L.; MOSMANN, T.R. Bidirectional cytokine interactions in the maternal-fetal relationship: is successful pregnancy a TH2 phenomenon? Immunoly. Today, v.14, p.353-356, 1993.). Furthermore, maternal and fetal cortisol released at the end of pregnancy and during labor is responsible for stress leukogram and the decrease of the functional activity of phagocytes (Chase et al.,2008CHASE, C.C.; HURLEY, D.J.; REBER, A.J. Neonatal immune development in the calf and its impact on vaccine response.Vet. Clin. N. Am. Food Anim. Pract., v.24, p.87-104, 2008.).

The immature immune system of newborn calves at birth emphasizes the critical role of passive immunity transfer from the dam. The bovine colostrum is rich in immunoglobulin G1 (IgG1), cells, and cytokines. Mononuclear leukocytes are the predominant cells in the mammary secretion, especially CD14+ macrophages (39.6%), B lymphocytes (24.5%), CD4+ T lymphocytes (13.8%), and CD8+ T lymphocytes (19%) (Park et al., 1992PARK, Y.H.; FOX, L.K.; HAMILTON, M.J.; DAVIS, W.C. Bovine Mononuclear leukocyte subpopulations in peripheral blood and mammary gland secretions during lactation. J. Dairy Sci., v.75, p.998-1006, 1992.). These cells are absorbed by the newborn intestinal mucosa and have been identified in the blood stream and lymph nodes after fresh colostrum intake (Liebler-Tenorioet al., 2002;Reberet al., 2006REBER, A.J.; LOCKWOOD, A.; HIPPEN, A.R.; HURLEY, D.J. Colostrum induced phenotypic and trafficking changes in maternal mononuclear cells in a pheripheral blood leukocyte model for study of leukocyte transfer to the neonatal calf. Vet. Immunol. Immunopathol.,v.109, p.139-150, 2006.).

The duration of immune factor presence in colostrum, especially IgG1, and the precocity of immune system development are the main factors in the epidemiological distribution of infectious diseases in calves. For determining the vulnerability periods, it is necessary to establish the hematological and immunological profiles of calves during early life.

Several studies have been performed to establish the normal values for hematological parameters. However, few published papers included repeated measurements of hemogram components in calves during the first 6 months of life. In addition, previous studies were performed using older technology (manual) (Brun-Hansen et al., 2006). Data on the profile of lymphocyte subsets in calves are scarce (Kampenet al., 2006KAMPEN, A.H., OLSEN, I.; TOLLERSRUD, T.; STORSET, A.K. et al. Lymphocyte subpopulations and neutrophil function in calves during the first 6 months of life. Vet. Immunol. Immunopathol., v.113, p.53-63, 2006.). At this time, we are aware of only two international papers published on this topic, and the results may not be representative for calves under Brazilian conditions (Wilson et al., 1996WILSON, R.A.; ZOLNAI, A.; RUDAS, P.; FRENYO, L.V. T-cell subsets in blood and lymphoid tissues obtained from fetal calves, maturing calves, and adult bovine. Vet. Immunol. Immunopathol.,v.53, p.49-60, 1996.; Kampenet al., 2006).

The hypothesis of this study is that variations in calves' hematological and immunological components occur during development, and these variations could indicate the window of susceptibility to antigens that are common in calf rearing. Therefore, a longitudinal study was designed to follow the cellular profile of Holstein calves from birth up to 6 months of age. This profile was evaluated by hemogram and phenotyping of the lymphocyte subsets.

MATERIALS AND METHODS

This research was approved by the Ethics Committee on Animal Use of the Faculty of Veterinary Medicine and Animal Science, University of São Paulo (Protocol # 2305/2011).

Ten Holstein cows and their calves were sourced from a dairy farm located in Nova Odessa, São Paulo, Brazil. These cows produced 25-30L of milk per day at the peak of lactation.

The dams were vaccinated against foot and mouth disease and Brucella abortus according to the Brazilian official program. These animals were also vaccinated in the pre-partum period by subcutaneous injection of 5mL of commercial multivalent vaccine containing inactivated strains of Bovine viral Diarrhea Virus (BVDV) type 1 (5960) isolated in Iowa (USA) and BVDV type 2 (53637) isolated in Ontario (USA); live/thermosensitiveBovine Herpesvirus 1 (Cooper) and Parainfluenza-3 Virus (RLB 103); live-attenuatedBovine Respiratory Syncytial Virus (strain 375) diluted in the adjuvant with "Quil A, cholesterol and amphigen." The vaccinations for bovine respiratory disease were administered twice, 8 and 4 weeks before the expected delivery dates.

Immediately after delivery, the dam was moved into a parlor where colostrum was collected aseptically from each quarter. Calves were fed with fresh colostrum from their respective dams. The calves were fed within 6h of birth with 2L of colostrum and with additional 2Lat12h after birth. An esophageal tube feeder was used only when the calves did not suckle from the bottle. The calves were transported from a dairy farm to the Ruminant Hospital at University of São Paulo,140km, in the second week after birth.

They were then fed with 6L of milk replacer (Sprayfo® Violeta, Stolen, Deventer, Holanda), commercial feed (Ração para bezerros®, Agromix, Sao Paulo, SP, Brazil), hay, mineral salt (Fosbovi 20®, Tortuga, Mairinque, SP, Brazil),and water ad libitum until weaning. The quantity of the feed was increased at the beginning of the transition period and the maximum amount was established to be 3kg/day.

The calves were assessed before colostrum administration (D0), every 2 days until the 10th day of life (D2 to D10), at the 15th day after birth (D15), and then monthly up to 6 months of age (D180).

The calves were given a general clinical examination that included vital signs, hydration, ocular mucous, capillary refill, and palpation of the lymph nodes. The organ systems were evaluated when animals showed any changes in the general clinical examination and data excluded at moment presented (Feitosa, 2014FEITOSA, F.L.F. Semiologia de recém-nascidos ruminantes e equídeos.Semiologia veterinária: a arte do diagnóstico. 3.ed. São Paulo: Roca, 2014. 627p.).

Blood samples (4mL) were collected by vein puncture of the external jugular vein, using a vacuum system, into tubes containing ethylenediamine tetraacetic acid (EDTA, 1.5mg/mL). All samples were transported under refrigeration in an isothermal box.

Hematological parameters were obtained using an automatic system (ABC Vet, Horiba ABX®, Montpellier, FRA). Differential counting of leukocytes was performed by observing the cell morphological characteristics at 1000xmagnification (Novo et al., 2015NOVO, S.M.F.; FREITAS, R.L.; SILVA, C.P.D.C. et al. Hematological adaptation in Holstein calves during the neonatal period. Braz. J. Vet. Res. Anim. Sci, v.52, p.212-216, 2015.).

The phenotyping of blood lymphocytes was performed according to the recommendations of Della Libera et al. (2012). The proportions of blood lymphocyte subsets were determined by flow cytometry (FACSCaliburTM, Becton Dickinson Biosciences, San Jose, CA, USA). One hundred microliters of whole blood with EDTA was added to the flow cytometry tubes. Red blood cells (RBCs) were lysed by adding FACS Lyse Solution (BD Biosciences). Monoclonal antibodies (VMRD, Pullman, WA, USA) against various bovine leukocyte surface molecules (Table 1) were added to a final concentration of 1μg/mL.The samples were stained for 30min at 4°C and washed thrice with phosphate buffered saline (PBS). Subsequently, the primary antibodies were labeled with 1μg/mL fluorescein isothiocyanate - FITC, 1μg/mL phycoerythrin- rPE (Invitrogen, Carlsbad, CA, USA), and 10μg/mL peridinin-chlorophyll proteins - PercP (Becton Dickinson Biosciences), and incubated for 30min in the dark at 4°C. The IgG1 specific antibody was conjugated with PerCP, the IgG2a specific antibody was conjugated with rPE, and the IgM specific antibody was conjugated with FITC. Finally, cells were washed twice and suspended in 300μL of cold, sterile PBS.

Table 1
Primary and secondaryantibodies used to identify blood mononuclear cells

Samples were analyzed by flow cytometry using FacsCalibur equipment (BD Biosciences, San Jose, CA, USA). Gate windows in forward angle scatter and 90º light scatter were established to allow the inclusion of the lymphocyte population.

Flowjo analysis software (Treestar Inc, San Carlos, USA) was used to analyze the events (50.000 cells/samples) acquired by flow cytometry. All samples were gated on forward angle and side scatter to establish the lymphocyte population. The lymphocyte subsets were analyzed based on the expression of specific fluorescence for CD3, CD4, CD8 and CD21.

Results are reported as the percentage of gated cells that were positive for each cell surface marker. The absolute number of each lymphocyte subset was calculated by multiplication of the percentage and the total number of lymphocytes per milliliter of blood obtained from the hemogram.

Statistical analysis was performed using SPSS for Windows (International Business Machines [IBM] Corporation, Armonk, New York, USA). All variables had parametric distribution according to the Shapiro-Wilk test, except rod neutrophils and eosinophils. Theage effect was examined using repeated measures analysis of variance(ANOVA). Differences among time points were considered significant when P< 0.05.

Rod neutrophils and eosinophils were not detected at some of the evaluation time points of this research. Therefore, these parameters were determined from D0 up to D6 for rod neutrophils, and from D60 up to D180 for eosinophils. These variables had non-parametric distribution according to the Skewness-Kurtosis test. Theage effect was examined using Friedman test, but none of the tested parameters showed statistically significant difference (P< 0.05) among time points.

RESULTS

The means and standard deviations of the erythrogram components and multiple comparisons between time points are shown in Table 2.

Table 2
Means and standard deviations of erythrogram components of Holstein calves from birth up to six months of age

Sample time on RBC had decreased from D2 to D6 with an increasing trend throughout the study. Significant differences were seen between D0 (before colostrum intake)to D4 and D6 (P< 0.05).

The maximum values for hemoglobin (HGB) and hematocrit (HCT) were observed on D0. These HCT values then decreased between D2 to D10, with a slight increase thereafter (D15 to D180). HCT values on D0 were significantly different from those on D4, D6, D8 and D10 (P< 0.05).

The values of mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC) decreased gradually during the first 6 months of life (D0 to D180). MCV values on D0 were significantly different compared with those from D6 up to D150 (P< 0.05), with the exception of D10. Values on D2 were different from those on D8, D30, D60, D120, D150 and D180 (P< 0.05). The mean MCV values on D4, 6, 8 and 10 differed from those on days 60, 120 and 150 (P< 0.05). MCH values on D2 and D8were different compared to those on D60 (P< 0.05).

The means and standard deviations of the leukogram components and multiple comparisons between time points are shown in Table 3.

Table 3
Means and standard deviations of leukogram components of Holstein calves from birth up to six months of age

Total leukocytes decreased from birth up to D6, after which time, the values increased slightly and remained constant from D8 to D180. The difference between the values on D0 and those on D6 was statistically significant (P< 0.05).

Relative and absolute values for segmented neutrophils showed some variations from D0 to D180. Relative values (%) on D0were higher than those on D6, 30, 60, 90 and 150 (P< 0.05). Absolute values (x103/µL) on D0 were significantly different from those on D6, D60, D150 and D180 (P< 0.05).

The relative and absolute values for monocytes varied slightly from D0 to D180. There were no statistically significant differences between the time points, despite the slight variations observed during this study. Relative and absolute lymphocyte values increased from D0 up to D180, and displayed some variations on D6, D30-D90 and D150-180. The number (%) of lymphocytes on D0 was lower than that on D6, D15, D30, D60, D90, D150 and D180 (P< 0.05).

Rod neutrophils and eosinophils were not detected at some of the time points included in this study. The minimum and maximum values observed for rod neutrophils were 1% (0.1 × 103/µL) on D6 and 3.8% (0.6 x 103/µL) on D2, respectively. Eosinophil numbers varied between 1% (0.1 × 103/µL) on D90 and 3% (0.2 × 103/µL) on D150. There were no statistically significant differences between time points for these parameters.

The means and standard deviations for lymphocyte subsets and multiple comparisons between time points are shown in Figure 1. Variations were detected in the proportions of CD3+ and CD21+ cells.

Figure 1
Mean and individual values of T and B lymphocytes population in blood of Holstein calves from birth up to six months of age

The mean relative values of CD3+ T lymphocytes did not change substantially in the first 10 days of life and then decreased (D15). The proportion of CD3+ (%) at D10 was higher than that observed on D30, D60, D90, D150 and D180 (P< 0.05). There were no statistically significant differences in the absolute values of CD3+ cells between time points.

The mean of absolute and relative values of the subsets CD4+ and CD8+ showed slight variations during the course of the study. There were no statistically significant differences between time points for these parameters.

The proportions (%) and absolute values of CD21+ lymphocytes increased significantly from D0 up to D30-D180. Differences in both parameters were detected between the early time points of D0, D2, D4, D8, D15 and the later time points of D30, D60, D90, D120 and D150.

By clinical parameters, all calves were healthy immediately after birth (D0). Navel inflammation and diarrhea were the most frequently observed disease conditions during the first fifteen days after birth. The frequencies of navel inflammation were 20% (2/10) from D2 up to D10 and increased to 50% by D15 (5/10,). Four cases of diarrhea were detected only on D15.

DISCUSSION

This study followed the hematological and immunological profiles of Holstein calves from birth up to 180 days of life.

Hemoconcentrationwas observed at birth, higher values of RBC, HGB and HCT in the first days of life are related of a physiological hemoconcentration due to fetal growth in a placental environment with low concentrations of O2. The components of the erythrogram are consistent with established reference ranges, according to Novo et al., (2015NOVO, S.M.F.; FREITAS, R.L.; SILVA, C.P.D.C. et al. Hematological adaptation in Holstein calves during the neonatal period. Braz. J. Vet. Res. Anim. Sci, v.52, p.212-216, 2015.), Benesiet al. (2012aBENESI, F.J.; TEIXEIRA, C.M.C.; LISBOA, J.A.N. et al. Eritrograma de bezerros sadios, da raça Holandesa, no primeiro mês de vida. Pesqui. Vet. Bras., v.32, p.357-360, 2012a.); Brun-Hansen et al., (2006). The subsequent decrease values is associated with the higher oncotic pressure and plasma dilution after colostrum administration. Moreover, low serum iron levels in neonates can compromise erythropoiesis (Mohriet al., 2004MOHRI, M.; SARRAFZADEH, F.; SEIFI, H. A.; FARZANEH, N. Effects of oral iron supplementation on some haematological parameters and iron biochemistry in neonatal dairy calves.Comp. Clin. Pathol., v.13, p.9-42, 2004.; Mohriet al., 2007).

The MCV values of newborn calves were highest at birth (46 fL) and then decreased subsequently. Erythrocyte size also decreased with advancing age, which probably occurs through the replacement of RBCs containing fetal HGB by smaller RBCs containing adult HGB (Knowles et al., 2000KNOWLES, T.G.; EDWARDS, J.E.; BAZELEY, K.J. et al. Changes in the blood biochemical and haematological profile of neonatal calves with age.Vet. Rec., v.147, p.593-598,2000.; Lee et al., 1971LEE, C.K.; ODELL, G.V.; ELIOT, F.P. et al. Postnatal loss of bovine fetal hemoglobin. Am. J. Vet. Res.v.32, p.1039, 1971). The decrease in hematimetric rates was concomitant with the increase of RBCs from the 10th day of life. These data are in agreement with variations reported in previous studies (Brun-Hansen et al., 2006).

The leukocytosis by neutrophilia observed around birth might be caused by the increase of maternal and fetal cortisol at the end of pregnancy and during labor. No evidence of eosinopenia profile was reported (Fagliariet al., 1998FAGLIARI, J.J.; SANTANA, A.E.; CAMPOS FILHO, E.; CURI, P.R. Blood constituents of the newborn Nelore cattle (Bosindicus), Holstein cattle (Bostaurus), and Murrah buffalo (Bubalusbubalis). Arq. Bras. Med. Vet. Zootec., v.50, p.253-262, 1998.; Benesiet al., 2012bBENESI, F.J.; TEIXEIRA, C.M.C.; LEAL, M.L.R. et al. Leukograms of healthy Holstein calves within the first month of life. Pesqui. Vet. Bras., v.32, p.352-356, 2012b.), since eosinophils cell concentration of calves are in small numbers in the blood of both young calves and adult animals. Transient increase in circulating neutrophils occurs because of the release of bone marrow cells and the marginal compartment for blood circulation. Furthermore, lower expression of l-selectin adhesion molecules on the surface of these cells in the presence of high cortisol levels has been reported (Nagahataet al., 2000NAGAHATA, H.; HIGUCHI, H.; YAMASHIKI, N.; YAMAGUCHI. M. Analysis of the functional characteristics of L-selectin and its expression on normal and CD18-deficient bovine neutrophils.Immunol.CellBiol., v.78, p.264-271, 2000.). Despite the reported neutrophilia, it is worth noting that the phagocytosis and bactericidal activity are decreased in neonate calves (Hauser et al., 1986HAUSER, M.A.; KOOB, M.D.; ROTH, J.A. Variation of neutrophil function with age in calves. Am. J. Vet. Res., v.47, p.152-153, 1986.).

Leukogram analysis and phenotyping of lymphocyte subsets allowed us to conclude that the total number of lymphocytes increased because of the increase in the proportion of CD21+ B cells after 30 days of life. The relative level of B lymphocytes detected in the first week after birth was low (9%), a value slightly higher than the mean value of 4% reported by Kampenet al. (2006KAMPEN, A.H., OLSEN, I.; TOLLERSRUD, T.; STORSET, A.K. et al. Lymphocyte subpopulations and neutrophil function in calves during the first 6 months of life. Vet. Immunol. Immunopathol., v.113, p.53-63, 2006.).

The cellular profile in the calves during the first weeks of life can be influenced by variations in the levels of progesterone, prostaglandin, and cytokines IL-4 and IL-10 transferred from dams to newborn calves through pregnancy (Chase et al., 2008CHASE, C.C.; HURLEY, D.J.; REBER, A.J. Neonatal immune development in the calf and its impact on vaccine response.Vet. Clin. N. Am. Food Anim. Pract., v.24, p.87-104, 2008.). Despite the Th2 cytokine profile at birth, the increase in the number of B lymphocytes presenting CD21+ receptor, which is expressed only in activated B cells, was observed only on the 30th day of life.

The late activation of B cells in neonates may be related to the low number of dendritic cells and low expression of major histocompatibility complex (MHC) class II by monocytes during the neonatal period (Reberet al., 2008aREBER, A.J.; DONOVAN D.C.; GABBARD, J. et al. Transfer of maternal colostral leukocytes promotes development of neonatal immune system: I- effects on monocyte lineage cells. Vet. Immunol. Immunopathol.,v.123, p.186-196, 2008a.; Reberet al., 2008b). Once a pathogen is recognized, it is internalized and processed by antigen-presenting cells (APCs). The peptides generated by APCs are expressed on the membranes of MHC II cells, which present the peptide to helper T lymphocytes (CD4+). The binding between MHC II and T lymphocyte receptor triggers events that result in the clonal expansion of T helper cells and enhanced cytokine production, which stimulate the proliferation of B lymphocytes and their differentiation to memory cells and plasma cells, which in turn produce antigen-specific immunoglobulins (McHeyzer-Williams, 2003).

Activated B cells could also act as APCs (McHeyzer-Williams, 2003). However, the reduced density of the CD21+ population in the first month of life can negatively impact B cell self-stimulation.

B cells migrate from the bone marrow to the secondary lymphoid tissues, where they go through the maturation process. Initially, naïve B cells are located in the primary lymphoid follicles, where they bind antigens and become activated. Then, the cells migrate to the germinal center portion for the selection and clonal expansion of antigen-specific B cells, where B lymphocytes are transformed to antibody-secreting plasma cells and memory B cells. The germinal center grows in size as the immune response is triggered by pathogens. It regresses and finally disappears when the infection is resolved. Germinal centers are present in the lymph nodes for about 3-4 weeks after initial antigen exposure, and subsequently leave via the efferent lymphatic vessels (Rudinand Thompson, 1998RUDIN, C.M.; THOMPSON, C.B. B-Cell Development and maturation. Semin. Oncol.,v.25, p.435-446, 1998.). The increase in activated B lymphocytes observed in this study could have been triggered by antigenic exposure. This phenomenon indicates that the maturation of specific immune system progresses in small steps from birth until puberty. Kampenet al. (2006KAMPEN, A.H., OLSEN, I.; TOLLERSRUD, T.; STORSET, A.K. et al. Lymphocyte subpopulations and neutrophil function in calves during the first 6 months of life. Vet. Immunol. Immunopathol., v.113, p.53-63, 2006.) and Chatthaet al. (2009CHATTHA, K.S.; FIRTH, M.A.; HODGINS, D.C.; SHEWEN, P.E. Age related variation in expression of CD21 and CD32 on bovine lymphocytes: a cross-sectional study.Vet. Immunol. Immunopathol.,v.130, p.70-78, 2009.) also reported a similar increase in lymphocytes after 30 days.

The low number of B lymphocytes may be responsible for colonization and infection by extracellular microorganisms that cause diarrhea and navel inflammation. These diseases were the main cause of data exclusion in this experiment on D8, D10 e D15.

The proportion of CD3+ T lymphocytes decreased from the 10th day of life. Variations in the proportions of CD3+ T lymphocytes could not be compared with those observed in the other studies owing to the scarcity of longitudinal studies evaluating the expression of this receptor from birth up to 6 months of age.

The proportions of CD4+ and CD8+ T lymphocytes were stable throughout the study period, with values of 23% and 10% at birth, and 21% and 10%, respectively, at 6 months of age. A similar proportion has been reported in earlier studies (Allen et al., 1996ALLEN, L.J.; KABBUR, M.B.; CULLOR, J.S. et al. Alterations in blood lymphocyte subpopulations and hematologic values in neonatal calves after administration of a combination of multiple-antigen vaccines. J. Am. Vet. Med. Assoc., v.209, p.638-642, 1996.; Ayoub and Yang, 1996AYOUB, I.A.; YANG, T.J. Age-dependent changes in peripheral blood lymphocyte subpopulations in cattle: a longitudinal study. Dev. Comp. Immunol., v.20, p.353-363, 1996.; Kampenet al., 2006KAMPEN, A.H., OLSEN, I.; TOLLERSRUD, T.; STORSET, A.K. et al. Lymphocyte subpopulations and neutrophil function in calves during the first 6 months of life. Vet. Immunol. Immunopathol., v.113, p.53-63, 2006.; Kulberget al., 2004KULBERG, S.; BOYSEN, P.; STORSET, A.K. Reference values for relative numbers of natural killer cells in cattle blood. Dev. Comp. Immunol., v.28, p.941-948, 2004.; Wilson et al., 1996WILSON, R.A.; ZOLNAI, A.; RUDAS, P.; FRENYO, L.V. T-cell subsets in blood and lymphoid tissues obtained from fetal calves, maturing calves, and adult bovine. Vet. Immunol. Immunopathol.,v.53, p.49-60, 1996.).

Hematologic and immune components of calves, as determined by hemoconcentration, stress leukogram, and the predominance of CD3+ T cells,varied with age, especially in the first month of life, when compared to CD21+ Bcells until 30 days of age. Subsequently, the lymphocyte populations increased due to the increase in CD21+ B cells.

Variation in the cell populations indicates that the neonatal period is a phase of increased susceptibility to infectious diseases. Therefore, extra care is neededto maintain the health and survival of the calves during this phase (Murray and Leslie, 2013MURRAY, C.F.; LESLIE, K.E. Newborn calf vitality: risk factors, characteristics, assessment, resulting outcomes and strategies for improvement. Vet. J., v.198, p.322-328, 2013.).

CONCLUSION

This research highlights the neonatal period as a critical stage in calf rearing. The study results also indicate that hematological profiles and subsets of lymphocytes of calves were functional and able to generate immune response in the calves after 30 days of life.

ACKNOWLEDGEMENTS

This work was supported by São Paulo Research Foundation [grant number 2010/015865-9].

REFERENCES

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Publication Dates

  • Publication in this collection
    Nov-Dec 2018

History

  • Received
    15 Sept 2016
  • Accepted
    31 Jan 2018
Universidade Federal de Minas Gerais, Escola de Veterinária Caixa Postal 567, 30123-970 Belo Horizonte MG - Brazil, Tel.: (55 31) 3409-2041, Tel.: (55 31) 3409-2042 - Belo Horizonte - MG - Brazil
E-mail: abmvz.artigo@gmail.com