Shipping suppresses lymphocyte blastogenic responses in Angus and Brahman X Angus feeder calves

Alteration of cellular immune responses by nutrition and weaning in calves

The effects of two levels of nutrition (400 g and 1000 g air dry matter milk substitute powder per day) and three ages of weaning (five, nine and 13 weeks) on cellular immune responses were determined in 32 calves. The lower level of nutrition was found to increase skin sensitivity responses to keyhole limpet haemocyanin (KLH) and decrease lymphocyte blastogenesis test (LBT) responses to ConA and pokewood mitogen (P < 0.05). Weaning at five weeks old resulted in increased KLH skin responses at nine weeks old compared with unweaned calves and decreased LBT responses to ConA and phyto-haemagglutinin at 10 weeks old compared with calves weaned at nine weeks old (P < 0.05). Weaning at five weeks old also increased peripheral blood concentrations of BoCD2+ and BoCD8+ lymphocytes (P < 0.05). The results show that the choice of husbandry conditions alters cellular immune responses in young calves and suggest that early weaning effects are essentially nutritional.

Bovine haptoglobin as a possible immunomodulator in the sera of transported calves

Bovine haptoglobin, which has been recognized as an acute phase protein following tissue injury and inflammation, was detected as a 33 k + 20 k Dalton fraction in the sera from calves transported by road for 2 days. The sera also possessed suppressive activity on lymphocyte proliferative response to concanavalin A. A significant correlation (r = 0.57, P < 0.05) was observed between haptoglobin concentrations and lymphocyte suppression in the sera. Furthermore, the haptoglobin fraction obtained from acute phase sera exerted dose-dependent suppression on lymphocyte blastogenesis. These circumstantial data suggest the possible involvement of bovine haptoglobin, at least in part, as an immunomodulator in serum suppression of lymphocyte blastogenesis in transported calves.

Effects of weaning on antibody responses in young calves

Two experiments were performed to investigate the effects of cessation of feeding milk substitute (weaning) on antibody responses to Keyhole Limpet haemocyanin (KLH) in young calves. In the first experiment, 47 calves were weaned at 42 days of age, while a further 47 calves remained unweaned until 84 days of age. All calves were immunized with KLH at 43 and 85 days of age. Serum IgG1, IgG2 and IgA responses to KLH were increased in the early weaned calves compared with the late weaned calves following both primary and secondary immunizations. In the second experiment, 24 calves were immunized with KLH at 21 days of age. Subsequently, at 35 days of age, eight calves were weaned, eight calves were sham-weaned and eight calves remained unweaned. Sham-weaning involved continuing to feed milk substitute of greatly decreased nutritional value in an attempt to isolate nutritional from behavioural effects of weaning. No effects of treatments on antibody responses were detected. It was concluded that weaning affects antibody responses to antigens given near weaning but not to antigens given 2 weeks before weaning.

Suppression of bovine lymphocyte and macrophage functions by sera from road-transported calves

Sera from calves which had been transported for 48 h resulted in impaired mitogen-stimulated blastogenesis of bovine lymphocytes and cytochrome c reduction activity of bovine alveolar macrophages. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis analysis revealed the appearance of 33 kDa and 20 kDa proteins in most of the sera after transportation. The proteins could have been related to the serum suppression.

Suppression of bovine neutrophil function by sera from cortisol-treated calves

The effect of sera from calves stressed due to cortisol administration was investigated on cytochrome c (CytC) reduction, chemotaxis and random migration under agarose of bovine neutrophils. CytC reduction was significantly suppressed by the sera, whereas the other two function indicators were unaffected. The serum suppressive factor(s) of CytC reduction remained unidentified following analysis using ultrafiltration and sodium dodecyl sulphate-polyacrylamide gel electrophoresis.

Model systems to study immunomodulation in domestic food animals

Development of immunomodulators for use in food producing animals is an active area of research. This research has generally incorporated aspects of immunosuppression in model systems. This methodology is appropriate because most of the research has been aimed at developing immunomodulators for certain economically significant diseases in which immunosuppression is believed to be an important component of their pathogenesis. The primary focus has been on stress-associated diseases (especially bovine respiratory disease), infectious diseases in young animals, and mastitis. The model systems used have limitations, but they have demonstrated that immunomodulators are capable of significantly increasing resistance to these important infectious disease syndromes. As our understanding of molecular immunology increases and as more potential immunomodulators become available, the use of relevant model systems should greatly aid advancement in the field of immunomodulation.

Rationale for using immunopotentiators in domestic food animals

In the production of domestic food animals several situations exist where disease decreases production efficiency. Some of these diseases are exacerbated by a lowered or compromised immune response of the host. If immunomodulators can be used to augment immune function at critical periods during the production of food animals, such as the neonatal period, and prior to or during exposure to stressors or pathogenic organisms, then the economic loss caused by infectious disease should be reduced.

Bovine recombinant interleukin-2 augments immunity and resistance to bovine herpesvirus infection

The in vivo administration of bovine recombinant interleukin-2 (rIL-2) was evaluated in calves vaccinated and then challenged with bovine herpesvirus-1 (BHV-1). In Experiment 1, 24 calves were allotted to four groups: control; bovine rIL-2; BHV-1 vaccine (modified-live); and bovine rIL-2 + BHV-1 vaccine. Serum neutralizing antibody titers to BHV-1 were increased sixfold, and virus shedding was fourfold less in calves vaccinated and treated with rIL-2 (25 micrograms/kg, intramuscularly) when compared to calves that received vaccine only. Treatment with rIL-2 induced lymphokine-activated killer activity that was eliminated by pretreating effector cells with complement and a monoclonal antibody (B26A) specific for the sheep red blood cell receptor. The rIL-2 treatment in BHV-1-vaccinated calves increased the calves' ability to withstand a BHV-1 challenge. However, during treatment with rIL-2, calves developed diarrhea and mild fever that abated after IL-2 treatment was stopped. A second experiment was then conducted to determine a dose of rIL-2 that would enhance immunity to BHV-1 without causing adverse side effects. Twenty-five calves were allotted to five groups that received injections of rIL-2 at 0.0, 25.0, 2.5, 0.25, or 0.025 micrograms kg-1 day-1 for 5 days. All calves received a modified-live BHV-1 vaccine. Calves treated with 25.0 micrograms kg-1 day-1 showed similar adverse side effects as in the first experiment but all other calves were normal. Compared to control calves, those treated with 25.0, 2.5, and 0.25 micrograms kg-1 day-1 of rIL-2 had higher (P less than 0.05) serum antibody titers to BHV-1 and following challenge lower (P less than 0.05) BHV-1 titers in nasal secretions; additionally, clinical disease as evidenced by nasal and ocular discharge was less severe (P less than 0.05). In vitro cytotoxic responses against BHV-1-infected bovine kidney cells were increased (P less than 0.05) in calves treated with rIL-2 in a dose dependent manner. These data suggest that bovine rIL-2 at 2.5 to 0.25 micrograms/kg may be an effective adjuvant to immunization.

Suppression of lymphocyte blastogenesis by sera from calves transported by road

The effect of sera from 4-h road-transported calves on mitogen-induced blastogenesis of bovine lymphocytes was investigated. Sera collected just after transportation showed a significant suppression (P less than 0.05) on blastogenesis. The immunosuppressive activity was reduced from those sera when they were treated with dextran-coated charcoal. Fractionation of the sera by ultrafiltration revealed that the activity was mainly concentrated in the fractions of molecular weights less than 50 kD.

Animal handling

Handlers with an understanding of animal behavior can handle livestock more efficiently and safely than handlers that lack an appreciation for the behavior of animals and their welfare. For example, four good handlers in a well-designed circular cattle-handling facility with a hydraulic squeeze could place an ear implant every 15 seconds or brand, vaccinate (up to four injections), place an ear implant, and castrate one animal every 45 seconds. Handlers that yelled at and prodded cattle excessively usually required more time to process each animal, due to wasted time when excited cattle escaped or became jammed in the squeeze. Veterinarians should teach clients the principles of animal behavior that relate to animal handling. Quiet, efficient handling will reduce stress and injuries to both people and livestock.

Influence of isoprinosine on bovine herpesvirus type-1 infection in cattle

A study was conducted to determine the in vivo efficacy of isoprinosine (ISO) in calves infected with bovine herpesvirus type-1 (BHV-1). Calves were infected with BHV-1 on day 0 and received ISO daily for 14 days. Clinical signs of disease, shedding of BHV-1, lymphocyte proliferative responses to mitogens, interleukin-2 production, and alveolar macrophage bactericidal activity were monitored during the study. Rectal temperatures were increased (P less than 0.05) in BHV-1 and ISO-BHV-1 calves at days 3 to 7 postinfection (PI). Isoprinosine did not influence BHV-1 shedding in calves. Lymphocyte proliferative responses to phytohemagglutinin (PHA) were lower (P less than 0.01) in BHV-1 calves when compared to control or ISO calves at day 4 PI, but ISO did not ameliorate this effect. Interleukin-2 activity was greater (P less than 0.05) in ISO-BHV-1 calves on days 4 and 8 PI in PHA-stimulated lymphocytes and on day 8 PI in concanavalin A-stimulated lymphocytes when compared to control, ISO or BHV-1 calves. Isoprinosine treatment of BHV-1-infected calves tended to decrease alveolar macrophage bactericidal activity. These data suggest that ISO does not reverse BHV-1 suppression of lymphocyte proliferation, but may enhance IL-2 production in BHV-1 infected calves.