Three subcutaneous injections of 0.20 mg of dexamethasone/kg of body weight caused a substantial increase in Babesia microti-parasitized RBC of hamsters, indicating that this was a useful method for revealing the presence of latent infections. A relative neutrophilia, lymphocytopenia, and eosinopenia were also seen in the long-term B microti-infected carrier hamsters after 0.20 mg or 0.02 mg of dexamethasone/kg. Noninfected hamsters treated with dexamethasone had a neutrophilic leukocytosis and a transient lymphocytopenia. Spleen to body weight ratios of noninfected hamsters decreased significantly (P less than 0.02) after 4 injections with either dosage level. These ratios did not significantly (P greater than 0.05) decrease in dexamethasone-treated infected hamsters.

Similar anamnestic antibody responses to a 2nd injection of a Anaplasma marginale vaccinal antigen were observed in calves infested with the tick Dermacentor albipictus and in tick-free calves. When challenge exposure of these calves to virulent A marginale was done, infestation with the tick Boophilus microplus increased anemia (P less than 0.01), but did not suppress antibody production to A marginale or increase parasitemia. None of the vaccinated calves, regardless of infestation, experienced clinical anaplasmosis. Mitogenic responses of lymphocytes from infested animals were unaltered by either infestation. Tick infestations did not cause immune suppression in the calves, whereas use of dexamethasone resulted in a significantly lower antibody response (P less than 0.05) after a 2nd injection of vaccinal antigen. After challenge with virulent A marginale, dexamethasone-treated calves showed more pronounced parasitemia (P less than 0.01) and anemia (P less than 0.01) than did control calves. Anaplasmosis did not prevent the calves from developing resistance to reinfestation, which was accompanied by immediate, but not delayed, hypersensitivity reactions against homologous tick extracts. Dermacentor albipictus did not seem to share common antigenic determinants with B microplus, since extracts from the latter did not elicit immediate hypersensitivity responses in calves sensitive to D albipictus extracts. Calves were somewhat resistant to reinfestation as evidenced by reduced numbers of adult fed ticks, decreased weights of ticks after feeding, and smaller egg masses.

The leukocyte migration inhibition test (LMIT) was used to assess cell-mediated immune responses of cattle against Anaplasma marginale. Leukocytes from 7 of 11 cows that had been cleared of the carrier state by antibiotic therapy 28 months earlier were inhibited from their normal migration by A. marginale antigens (P<0.001). After reexposure to virulent organisms, all animals were positive to the LMIT. There was not a significant relationship (r=0.49) between LMIT values before and after reexposure.

The prophylactic efficacy of a long-acting oxytetracycline formulation was determined in 36 susceptible cows experimentally inoculated with Anaplasma marginale. Each of 10 cows in 3 treatment groups (T2, T3, T4) were given IM injections of 20 mg of oxytetracycline/kg of body weight once, twice, or three times during the prepatent period. The T2 group was treated once at 1 week after experimental inoculation, the T3 group was treated 2 times (at 1 and 2 weeks) after exposure, and the T4 group was treated 3 times (at 1, 2, and 3 weeks) after exposure. Six cows comprising group T1 served as nonmedicated controls. Treatment of cattle in the prepatent period with the long-acting oxytetracycline formulation produced significantly fewer clinical anaplasmosis cases. This reduction in frequency was proportional to the number of weekly treatments given. In cattle which developed clinical disease, only 1 IM injection of 20 mg of oxytetracycline/kg was necessary to induce recovery. The prepatent period in the treated cattle was extended approximately 30 days beyond the prepatent period of the control cattle after their final treatment. Humoral rapid card agglutinating and complement fixing antibodies regularly were present in the cows 10 days after they were inoculated; however, neither the presence of antibody nor that of the antibiotic was sufficient to prevent establishment of the carrier state in the principals.

The effects of moderate maternal protein restriction on in vivo humoral and cell-mediated immune responses of bovine neonates were studied. Hereford heifers were fed protein-adequate or protein-restricted rations for the last 150 days of gestation and for 6 months after parturition. At birth, all calves from these heifers were allowed to remain with their dams and were inoculated with tetanus toxoid (TT) and an emulsion of tuberculoproteins and trehalose dimycolate (cord factor) of Mycobacterium bovis. One month later, blood samples were collected from all calves, and sera were examined for antibodies to TT. The calves were given a 2nd inoculation of TT, and anamnestic antibody responses were measured 7 days later. Differences in primary or secondary antibody responses were not observed between principal and control groups of calves. Also, differences in tuberculin reactivity were not observed in calves from cows fed protein-adequate or protein-restricted diets.

Two methods were used to clarify bovine colostrum for quantitation of total complement (C') hemolytic activity in the whey. The renin precipitation method produced whey which tended to have higher C' hemolytic activity (5.0 +/- 3.4 CH50 units) than did whey prepared by ultracentrifugation (2.5 +/- 2.6 CH50 units) although this difference was not significant. No correlation was found between levels of complement in the sera of cows at parturition and in the colostral whey from the same animal. Total complement activity was not detected in milk taken a 96 hours or one month after parturition. This is apparently the first report of quantitation of total C' hemolytic activity in bovine colostrum.

Blood samples from 16 anaplasmosis complement-fixation (CF) positive sheep from a flock near Cambridge, Idaho, were inoculated into 3 intact sheep and 3 splenectomized calves. The 3 sheep became CF positive, and 2 developed parasitemia. None of the 3 calves had signs of anaplasmosis, but all became ill when they were subsequently challenge exposed with blood from known carriers of Anaplasma marginale. After a 75-day observation period, blood from the recipient intact sheep was subinoculated into 3 splenectomized sheep. These splenectomized sheep developed clinical anaplasmosis and became CF positive. In only 1 sheep was there a positive rapid card agglutination test. Therefore, the rapid card agglutination test was not considered to be diagnostic for anaplasmosis carrier status in sheep. Electron microscopic studies were performed on infected sheep erythrocytes to determine the morphologic structure of the organism involved. The causative organism was determined to be Anaplasma ovis.

Beef heifers were fed protein- or energy-deficient rations (or both) for approximately the last 5 months of pregnancy. Serum samples were periodically collected and were analyzed for amounts of total complement (C) hemolytic activity. After being fed the rations for approximately 2 months, heifers given low-energy rations had significantly lower (P < 0.01) amounts of C than did those fed adequate energy rations, This decrease in C was observed regardless of the amount of dietary protein, although low protein intake seemed to exaggerate the effect of low energy consumption. Reduced protein in the rations had no effect on C titers when caloric intake was adequate. Also, the depressive effect of low dietary energy on C values was no longer apparent after approximately 4 months of feeding the rations. Amounts of C dropped by 20 to 40 U for all groups at or near the time of parturition. The C values averaged over all test dates were significantly lower (P < 0.05) for those heifers given low energy in their rations as compared with values for heifers fed adequate energy rations (146.9 vs 160.8 U).

Beef cows were placed on protein-deficient and/or energy deficient rations for the last 150 days of pregnancy. After birth their calves were placed on 1 or 21 C environmental chambers for 3 days, and sera were collected for determination of complement (C) levels. At birth, the mean complement hemolytic (CH50) titer of all calves was 46.0 +/- 1.7 units, but the titer rapidly dropped (P < 0.01) to 31.6 +/- 1.2 by 12 hours after birth. Levels of C activity then began to rise and reached a mean titer of 76.3 +/- 3.0 by 3 days of age. A quadratic curve of predicted CH50 values was constructed from the data. Differences between principal and control groups of calves were not detected. These results suggest that maternal protein-calorie deprivation and limited cold stresses have little effect on levels of C activity in the bovine neonate. Possible explanations for the decrease in CH50 levels after birth are discussed.

The effects of maternal protein or calorie deprivation (or both) on the bactericidal activity of neutrophils and sera from newborn calves subjected to cold stress were studied. Nutritional deficiencies in the dam had little effect on in vitro bactericidal activity of neutrophils and base-line sera taken at birth. Neutrophils obtained at birth destroyed Staphylococcus aureus but not Escherichia coli when incubated with either unheated or heated autologous base-line sera. Heat treatment of base-line sera to inactivate complement did not alter bacterial growth. When incubated in the presence of autologous base-line sera, neutrophils from 3-day-old calves were no more active in the destruction of either bacterium than were neutrophils from newborn calves. However, addition of day 3 (immunoglobulin-containing) sera enabled day 3 neutrophils to destroy E coli (P < 0.0001). The increased destruction of E coli by day 3 neutrophils and day 3 sera was not affected by heat treatment of the sera. Maternal protein deficiency significantly increased (P < 0.05) destruction of E coli by day 3 neutrophils and sera. This effect was independent of energy levels. There were no differences observed in the bactericidal activity of neutrophils and sera taken from calves exposed to 1 C or 21 C environmental chambers for 3 days. Also, cold stress-nutritional stress interactions were not detected.

The ultrastructural appearance of bovine fetal thymocytes forming non-immune spontaneous erythrocyte rosettes was studied. The thymocytes-forming rosettes were found to be small, intermitotic lymphocytes. The attachment between the thymocytes and the erythrocytes were usually observed as small contact points.

Anaplasmosis was experimentally transmitted from cattle to elk to cattle. Six non-splenectomized adult elk (Cervus canadensis canadensis) that were inoculated with freshly collected heparinized blood from cattle chronically infected with Anaplasma marginale became asymptomatic carriers. Although the exposed elk did not develop clinical or hematologic evidence of infection they become seropositive by the serum and plasma rapid card agglutination (RCA) tests. Blood from the experimentally infected elk produced disease in splenectomized bovine calves and the carrier state persisted for at least one year. Infection did not occur when two elk were inoculated with 0.5 ml of frozen blood from known bovine carriers. The blood had been frozen for four weeks in liquid nitrogen with six percent dimethyl-sulfoxide.

Total haemolytic complement (CH50) activities of sera obtained from newborn dairy calves and their corresponding dams were compared. The differences between the mean maternal and neonatal CH50 concentrations were significant (P less than or equal 0.001). The concentration of CH50 units/ml in sera from 16 calves was 52.0 +/- 21.4, whereas, for the cows it was 195.8 +/- 24.0. The ratio of cow: calf serum CH50 values averaged 4.24 with a range from 1.77 to 8.00. A positive rank correlation of 0.479 (P less than 0.05) was found between the CH50 titres in calves and their dams. Anticomplementary substances were not detected in calf sera. The possible relationships betweeen deficient CH50 levels in newborn calves and their susceptibility to infectious agents is discussed.

A whole blood culture technique was used to evaluate the influence of phytohemagglutinin (pha), concanavalin A (Con A), and pokeweed mitogen (pwm) on the in vitro response of peripheral blood lymphocytes from bovine fetuses and adult cattle. Dosage response curves for pha, Con A, and pwm were determined for bovine peripheral blood lymphocytes incubated for different durations. Lymphocytes from 10- to 14-month-old cattle responded most dramatically to Con A. Responses to pwm and pha were similar but not as high. The blastogenic responses of lymphocytes from 100 fetuses, ranging in estimated gestational age from 78 to 240 days, were examined. As fetal age increased, there was a general increase in responsiveness to Con A and pwm, but a less pronounced increase for pha. There were highly significant correlations (P ≤ 0.01) between the blastogenic responses induced by each of the 3 pairings of phytomitogens in fetuses of gestational age 181 to 240 days. The highest correlation was between blastogenic responses to Con A and pwm for the fetuses of gestational age 181 to 240 and 78 to 240 days. Linear and multiple regression equations for predicting blastogenic response for fetal lymphocytes from crown-rump length and weight were formulated. Data from lymphocyte responses to pwm and Con A were comparable in predictability, whereas prediction of response to pha was minimal. As gestational age increased, there was an increase in the percentage of fetuses that gave a significant response to each phytomitogen. After 90 days’ gestational age, lymphocytes from most fetuses had significant blastogenic responses to pwm. Similarly, after 121 days, 50% or more responded to Con A. However, only 15 of 100 fetuses had significant responses to pha and in no fetal age group studied did the majority respond. Significant blastogenic responses to Con A were observed in 58 of 100 fetuses. Since Con A and pha are both thought to stimulate the T-lymphocyte cell system, the results probably indicate that they stimulate different subpopulations of T-lymphocytes and that in cattle there is a marked separation of in vitro cellular immune functions of peripheral blood lymphocytes during ontogeny. Measurement of transformation responses is commonly used as a measure of immunologic reactivity of the cell donor, and significant mitogenic responses in some but not other fetuses of the same age imply that some bovine fetuses may be immunologically more capable than others.

The bactericidal capacity of serum and peripheral blood leukocytes from newborn dairy calves (before receiving colostrum) and their dams for a strain of Escherichia coli and Staphylococcus aureus has been investigated. Comparative studies were conducted, using either unheated (freshly collected) and heated serums alone or in combination with cells from adult and newborn animals. Neither serum from newborn calves was able to kill either microorganism. Both microorganisms were sensitive to bactericidal activity of antibody and complement in unheated serum from adult cattle. On heating, serum from adult cattle lost bactericidal properties of the antibody-complement system. A cellular deficiency in phagocyte function in cells of newborn dairy calves was not evident, since they were as able to kill E coli and S aureus as cells from adult cattle, when incubated in the presence of the same opsonic source. Bactericidial activity was not evident when cells from newborn calves were incubated with heated autologous calf serum and S aureus or E coli. Unheated, autologous calf serum combined with cells from newborn calves exerted bactericidal capacity against S aureus but not E coli. The bactericidal capacity against S aureus of cells from newborn calves incubated with unheated serum from newborn calves did not differ from heated serum from adult cattle. However, there was a difference with E coli. The reasons for this phenomenon have not been determined, but may relate to natural, specific immunity of the neonate. Immunoglobulin and antibody concentrations in serums from calves and dams were determined. Most of the dams had bacterial agglutination titers to both microorganisms; the calves had either undetectable or low levels of antibody.