Humoral immune response of water buffalo monitored with three different antigens of Toxocara vitulorum

Humoral immune response of water buffalo naturally infected with Toxocara vitulorum was monitored using three different antigens of this parasite in serum and colostrum of buffalo cows and calves. Soluble extract (Ex) and excretory/secretory (ES) larval antigens and perienteric fluid antigen (Pe) of adult T. vitulorum were used to measure the antibody levels by an indirect ELISA. Serum of 7-12 buffalo cows for the first 365 days and colostrum of the same number of buffalo cows for the first 60 days of parturition, and serum of 8-10 buffalo calves for the first 365 days after birth were assayed. The ELISA detected antibodies against all three T. vitulorum antigens in the colostrum and serum of 100% of buffalo cows and calves examined. The highest antibody levels against Ex, ES and Pe antigens were detected in the buffalo cow sera during the perinatal period and were maintained at high levels through 300 days after parturition. On the other hand, colostrum antibody concentrations of all three antigens were highest on the first day post-parturition, but decreased sharply during the first 15 days. Concomitantly to the monitoring of immune response, the parasitic status of the calves was also evaluated. In calves, antibodies passively acquired were at the highest concentrations 24 h after birth and remained at high levels until 45 days coincidentally with the peak of T. vitulorum infection. The rejection of the worms by the calves occurred simultaneously with the decline of antibody levels, which reached their lowest levels between 76 and 150 days. Thereafter, probably because of the presence of adults/larvae stimulation, the calves acquired active immunity and the antibodies started to increase slightly in the serum and plateaued between the days 211 and 365. All three antigens were detected by the serum antibodies of buffalo calves; however, the concentration of anti-Pe antibody was higher than anti-EX and anti-ES, particularly after 90 days of age. By conclusion, the buffalo cows develop immunity and keep high levels of antibodies against T. vitulorum-Ex, ES and Pe antigens and these antibodies are transferred to their calves through the colostrum. This passively acquired immunity does not protect the calves against the acquisition of the infection, but these antibodies, passively or actively acquired, may have an important role during worm rejection by the calves and prevention of intestinal reinfection.     

Hematologic values in calves during the first 6 months of life

BACKGROUND: Age-related changes in hematologic values are known to occur in many species. Few published studies include repeated measurements of hematologic parameters in calves during the first months of life. OBJECTIVE: The aim of the present study was to monitor hematologic values by sequential measurements from birth to 6 months of age in 15 healthy calves of the Norwegian Red breed, and compare the results to reference intervals for adult, lactating dairy cows. METHODS: Fifteen clinically healthy calves were sampled every week during the first 5 weeks of life and every month thereafter until 6 months of age. Hematologic values were measured using the ADVIA 120 hematology system. Reference intervals were determined for 75 healthy adult cows of the same breed. RESULTS: Compared with adult reference intervals, the MCV was lower and the RBC count was higher in calves throughout the investigation period. Hemoglobin concentration stayed largely within the adult reference interval. Mean MCHC was lower than adult values for 5 weeks, then increased and reached adult values by weeks 10-12. The mean lymphocyte count for calves reached adult reference values at weeks 6-8, and the mean monocyte count increased steadily until weeks 14-16. For most leukocytes, interindividual variation was larger during the first 5-8 weeks of life. The mean platelet count for calves was higher than the adult reference interval until weeks 19-21 of age. CONCLUSIONS: Age-specific reference intervals for calves from birth to 6 month of age are needed for RBC count, MCV, MCHC, red cell distribution width, and platelet and lymphocyte counts.     

An enzyme-linked immunosorbent assay (ELISA) for detection of antibodies against Toxocara vitulorum in water buffaloes

Toxocara vitulorum, a parasite of the small intestine of cattle and water buffaloes, is mainly acquired by calves via the colostrum/milk from infected cows. To understand the development of immune responses in calves, antibody levels to a soluble extract antigen (Ex) from T. vitulorum infective larvae were measured by an indirect ELISA with sera of 15 buffalo calves, which were sampled every 15 days for the first 180 days after birth and 9 buffalo cows during the perinatal period. From all serum samples examined during the first 180 days, antibody level was lowest and highest in calves at 1 day of age before and after suckling colostrum, respectively, suggesting that the origin of antibodies was the colostrum. Immediately after birth, antibody levels in suckled calves remained at high levels until day 15, began to decrease to lower levels between 15 and 30 days and remained relatively stable until 120 days. By comparing the immune responses of these animals with their parasitological status it was considered possible to determine if passively acquired or actively produced antibodies provided protection against the infection. High numbers of T. vitulorum eggs in the feces between 30 and 60 days indicated that passively acquired antibodies did not provide protection against the infection, at least during these first days, and the maximum fecal egg counts during 30-45 days were coincident with decreased antibody levels. Between 60 and 120 days, when serum antibodies were detected at reduced, but stable levels, adult nematodes were expelled from the intestines and no more T. vitulorum eggs were found, suggesting development of acquired resistance. However, the potential and functional protective role of the antibodies against T. vitulorum infection and the process of self-cure requires further investigation.     

Eimeria infections in cows in the periparturient phase and their calves: oocyst excretion and levels of specific serum and colostrum antibodies.

Faecal Eimeria oocyst excretion and levels of antibodies to first generation merozoite antigen of E. bovis in sera and colostra were followed in 86 and 70 cow-calf pairs in northern (group EF) and central Germany (group H), respectively, over periods of 3 weeks before to 3 weeks after calving in cows and from birth to an age of 63 days in calves. Oocysts were found in 30 and 7.7% of cows in groups EF and H, respectively. They belonged to 10 (group EF) and four Eimeria spp. (group H) with E. bovis, E. ellipsoidalis, E. auburnensis and E. zuerni as the most frequently occurring species. Prevalence and intensity of oocyst excretion varied with time resulting in peak values around the date of parturition, particularly in the case of E. bovis. Peak values at the time of parturition were also seen in case of strongyle egg excretion. Seven (group H) and nine Eimeria spp. (group EF) were found in the calves. The predominant species E. ellipsoidalis, E. zuerni, E. bovis and E. auburnensis were detected for the first time earlier after birth (3-5 weeks) than the others. The prevalence of Eimeria infections increased to 67.1% (group EF) and 50.1% (group H) 9 weeks after birth. Specific IgM and IgA antibody levels (the latter only determined in group EF) in cow sera remained almost constant throughout the observation period, whereas IgG(1) and IgG(2) levels were reduced at the time of parturition. Levels of specific antibodies in sera and colostra were significantly correlated. Except IgM antibodies, significant inverse correlations were found in cows between intensity of infection with E. bovis and specific serum IgG (group H) and IgG(2) (group EF) antibodies. Antibodies to E. bovis were detected in calves sera only after colostrum intake with significant correlations between levels in calves sera and colostra. Levels decreased, starting within the first week of life (most conspicuously in case of IgM and IgA) until the third week. Subsequently, but except IgG(1) antibody concentrations increased until the end of the observation period. Interrelations between antibody levels and the total amount of E. bovis oocysts excreted by the calves until the ninth week of life varied with the age of the animals. Inverse relationships in the first 3 weeks of life as suggested by negative correlation coefficients could not be proven statistically. Thus, there is no unambiguous proof for immunoprotection of calves against E. bovis via maternal immunity. Considering antibody levels in the 3-9 weeks old calves significant direct correlations with E. bovis oocyst excretion were found in case of IgM, IgG(2) and IgA, reflecting an active immune response of young calves to coccidial infection.     

Colostral transfer of gamma glutamyl transpeptidase in calves

Serum gamma glutamyl transpeptidase (GGT) levels in blood samples taken from normal calves which bad suckled colostrum were much higher than those found in healthy adult cattle. Levels of over 60 times the normal adult level were observed. These high levels of GGT took approximately 5 weeks to decline to adult values. Calves which appeared to have not received or absorbed colostrum had GGT levels which would be considered normal in adult cattle. A calf with serum gamma globulin levels which indicated an intermediate amount of colostrum absorption had a level of GGT which was intermediate between that expected for normal adult cattle and that found in calves which had more fully absorbed colostrum. The mean GGT level observed in colostrum from 6 newly-calved cows was over 800 times the mean serum GGT level of the same 6 cows. It therefore appears most likely that GGT is concurrently absorbed with colostrum by calves and this gives rise to the very high levels seen in normal calves. Calves with very high levels of serum GGT also had raised levels of alkaline phosphatase (AP) which slowly declined but never reached normal adult levels within the 53-day period of observation. It therefore appears that high levels of both GGT and AP are achieved by calves at the time of colostrum absorption and it is concluded that clinical interpretation of serum GGT and AP levels in young calves is closely dependent upon parallel knowledge of their serum gamma globulin levels.     

Colostral transfer of gamma glutamyl transpeptidase in calves

Serum gamma glutamyl transpeptidase (GGT) levels in blood samples taken from normal calves which bad suckled colostrum were much higher than those found in healthy adult cattle. Levels of over 60 times the normal adult level were observed. These high levels of GGT took approximately 5 weeks to decline to adult values. Calves which appeared to have not received or absorbed colostrum had GGT levels which would be considered normal in adult cattle. A calf with serum gamma globulin levels which indicated an intermediate amount of colostrum absorption had a level of GGT which was intermediate between that expected for normal adult cattle and that found in calves which had more fully absorbed colostrum. The mean GGT level observed in colostrum from 6 newly-calved cows was over 800 times the mean serum GGT level of the same 6 cows. It therefore appears most likely that GGT is concurrently absorbed with colostrum by calves and this gives rise to the very high levels seen in normal calves.

Calves with very high levels of serum GGT also had raised levels of alkaline phosphatase (AP) which slowly declined but never reached normal adult levels within the 53-day period of observation.

It therefore appears that high levels of both GGT and AP are achieved by calves at the time of colostrum absorption and it is concluded that clinical interpretation of serum GGT and AP levels in young calves is closely dependent upon parallel knowledge of their serum gamma globulin levels.     

Kinetics of detection of blastogenic responses of neonatal calves inoculated in utero with tetanus toxoid, killed Mycobacterium bovis, and killed Brucella abortus.

Nine pregnant cows were laparotomized and their fetuses were immunized with tetanus toxoid, killed Brucella abortus, and killed Mycobacterium bovis. Blastogenesis assays and total leukocyte and differential counts were done when the calves were 1, 2, 3, 7, 14, 21, 28, and 60 days of age. Initial blastogenesis responses to antigens, phytohemagglutinin, and concanavalin A were not positive as frequently as were the responses obtained when the calves were 2 to 3 weeks of age. The probability of obtaining a positive response to an antigen was positively correlated with the magnitude of the response, as determined by delayed-type hypersensitivity skin reactions. Leukocyte and differential WBC counts in immunized calves were similar to those of unimmunized calves. The mean leukocyte count for the immunized calves remained near 16,000 cells/mm3; blood obtained in the first few days after birth contained a greater number of neutrophils than lymphocytes, whereas lymphocyte-to-neutrophil ratio gradually approached those of adult cattle, in which lymphocytes predominate.     

Blood serum tocopherol levels in calves born from cows winter fed hay or grass silage.

Blood serum tocopherol was determined in 44 calves born in the spring from cows that had been fed either timothy grass silage or timothy hay produced in Norther Ontario. On all sampling dates (at birth and at eight, 21, 35 and 60 days of age), calves from the silage group had higher average tocopherol levels than those from the hay group. Studies on serum tocopherol distribution in cows and their calves obtained 60 days after birth from the silage group showed that alpha-tocopherol averaged 85% and beta + gamma-tocopherols 12%. Only trace quantities of delta-tocopherol were detected in the serum of cows but none in those of calves.     

Effects of the ingestion of whole colostrum or cell-free colostrum on the capacity of leukocytes in newborn calves to stimulate or respond in one-way mixed leukocyte cultures

OBJECTIVE: To evaluate effects of colostral cells on the ability of neonatal leukocytes to respond in a mixed leukocyte response (MLR) as a means of evaluating specific immune responsiveness. ANIMALS: 10 Holstein calves, their respective dams, and 10 unrelated adult Holstein cows. PROCEDURE: Soon after birth, their calves were fed maternal whole colostrum or colostrum after cells were removed by centrifugation. Responses for leukocytes obtained from calves during the first 5 weeks after birth, their dams, and unrelated cows were measured by use of 1-way MLR as an indicator of immune development. An internal control treatment, proliferation of lymphocytes stimulated with Staphylococcus enterotoxin B (SEB), was also measured. RESULTS: Transfer of colostral leukocytes had a significant effect on the MLR and SEB-induced response in calves. Calves receiving whole colostrum had enhanced responses to maternal and unrelated leukocytes 24 hours after ingestion of colostrum. These responses decreased quickly, indicating direct modulation of the neonatal immune response. Calves receiving whole colostrum effectively stimulated the MLR by 24 hours after ingestion of colostrum. In contrast, calves receiving acellular colostrum did not effectively stimulate the MLR until 2 to 3 weeks after birth. CONCLUSIONS AND CLINICAL RELEVANCE: Ingestion of maternal colostral leukocytes immediately after birth stimulates development of the neonatal immune system. These maternal leukocytes enhance development of antigen-presenting capacity as indicated by their ability to stimulate the MLR and SEB response. The influence of ingested maternal cells on neonatal immunity was also indicated by a reduction in reactivity of neonatal cells to maternal alloantigens.     

Colostral transfer of bovine immunoglobulin E and dynamics of serum IgE in calves

The role of IgE in protective immunity is becoming understood, therefore the colostral transfer of IgE and the age-dependent changes of IgE levels may be important for neonatal immunity. To investigate this question, serum samples were collected from range-fed Hereford cows and their calves from birth through 9 months of age. The sera were assayed for total IgE by enzyme-linked immunosorbent assay (ELISA). Calves were found to have significant levels of IgE during the first week postpartum, indicating colostral transfer of IgE. Thereafter, serum levels declined rapidly within 3 weeks from birth. The IgE levels began to increase after 12 weeks of age, and in some cases reached adult levels. The passive transfer of maternal IgE through colostrum may be important in providing early protection from disease, especially against intestinal parasites.     

Hematologic values in newborn beef calves.

Hematologic values were determined in 35 beef calves at birth, at 24 and 48 hours, and in 22 of these calves at 3 weeks after birth. Thirty calves did not have clinical signs of disease throughout the 3-week period. Variables that changed significantly over time in these healthy calves included hematocrit, RBC count, hemoglobin concentration, mean cell volume, mean cell hemoglobin concentration, WBC count, neutrophil-to-lymphocyte ratio, and plasma total protein and serum immunoglobulin concentrations. Of the 35 calves, 5 had clinical signs of disease at 3 weeks. Comparison of hematologic values from these calves with values for healthy calves revealed significant differences at each sample collection time, although disease was not evident at the 3 early sample times. The band neutrophil count and the neutrophil-to-lymphocyte ratio differed between the 2 groups at birth. At 24 hours, the monocyte count was higher in the 5 ill calves. At 48 hours, total leukocyte, mature neutrophil, and monocyte counts, and neutrophil-to-lymphocyte ratio also were higher in the 5 calves. At 3 weeks when clinical signs of disease were detectable in the 5 calves, the total leukocyte, band neutrophil, and mature neutrophil counts, neutrophil-to-lymphocyte ratio, and plasma total protein and fibrinogen concentrations were higher.(ABSTRACT TRUNCATED AT 250 WORDS)     

Epidemiologic factors and isotype-specific antibody responses in serum and mucosal secretions of dairy calves with bovine coronavirus respiratory tract and enteric tract infections.

Blood, feces, and nasal swabs specimens were collected 12 to 24 hours after birth and then 3 times/week (blood only once per week) from one group of 10 calves until they were 10 weeks old and from a second group of 10 calves until they were 10 to 20 weeks old. Colostrum was collected from all calves' dams and tears from 5 randomly selected calves in the first group. All fecal and nasal specimens were assayed for bovine coronavirus (BCV) antigens by ELISA. Nasal epithelial cells were examined for BCV antigens by direct immunofluorescence. Isotype antibody titers to BCV in all samples from 5 calves in group 1 were evaluated by ELISA. Zinc sulfate turbidity (ZST) values were determined on the first serum samples taken from all calves in group 1. To determine whether any correlation existed between ZST values, isotype antibody titers to BCV (12 to 24 hours after birth), number of respiratory sick days, number of enteric sick days, or days to first shedding of virus, a Spearman rank order correlation coefficient was done. Bovine coronavirus respiratory tract and enteric tract infections were common on this farm. Most initial infections developed when calves were 1 to 3 weeks old; however, there were also multiple incidences of shedding of viral antigens or seroconversions at later times during the study. Persistence of infection or reinfection of the upper respiratory tract with BCV was common. Colostral antibody titers to BCV (IgG1) were in all cows at moderate amounts; however, calf serum antibody titers and ZST values (12 to 24 hours after birth) were highly variable.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lipid peroxides and antioxidants in serum of neonatal calves

OBJECTIVE: To examine the association between oxidative stress and antioxidants in neonatal calves after birth. SAMPLE POPULATION: Sera from 6 healthy Holstein-Friesian cows and 7 of their newborn calves were obtained at various intervals after birth. PROCEDURE: Lipid peroxides in serum of cows and their newborn calves were estimated by measuring concentrations of thiobarbituric acid-reactive substances (TBARS). The antioxidative activities of neonatal sera were evaluated by measuring their superoxide-scavenging activities, ferroxidase activities, and the concentration of bilirubin-associated albumin. RESULTS: Concentration of TBARS in neonatal sera within 1 day after birth was significantly higher than concentrations > or = 2 days after birth and concentrations in serum of the dams. In contrast, antioxidative activities of neonatal sera, evaluated on the basis of superoxide-scavenging activities, ferroxidase activities, and concentration of bilirubin-associated albumin 3 hours after birth, were significantly lower than antioxidative activities in sera of the dams. CONCLUSIONS: Susceptibility of calves to oxidative stress during the neonatal period may be explained by the immature defense system against superoxide radicals.     

Bovine chlamydial abortion: serodiagnosis by modified complement-fixation and indirect inclusion fluorescence tests and enzyme-linked immunosorbent assay

Sequential serum samples from 11 cows experimentally inoculated with different abortigenic strains of Chlamydia psittaci were tested by a modified complement-fixation (MoCF) test, an indirect inclusion fluorescence antibody (IIFA) test, and an enzyme-linked immunosorbent assay (ELISA). One of these cows was not pregnant, another gave birth at term to a healthy calf, and all the others prematurely delivered infected dead calves or weak live calves. The results achieved with these tests on sera of 3 of the cows were compared with those from the previously used standard complement-fixation (CF) test. Six of 11 cows had detectable preinoculation titers between 1:8 and 1:16 when tested by the MoCF test, yet preinoculation titers were not detected by CF. In contrast, 9 of 11 and 10 of 11 preinoculation samples had detectable chlamydia-specific antibodies when examined by the IIFA test and the ELISA, respectively. The preinoculation IIFA titers ranged from 1:8 to 1:64, and the ELISA optical density values varied from 0.150 to 0.450. All cows responded with significant increases in antibody levels detected by the MoCF test, the IIFA test, and ELISA after they were experimentally inoculated and after they aborted or delivered infected calves. Overall, the dynamics of the antibody responses were found to be similar with the 3 different serologic techniques. When cows aborted later than 36 days after they were inoculated, the antibody response was biphasic, whereby the more pronounced responses occurred after the abortion occurred. The nonpregnant cow and the cow that delivered a healthy calf at term had only one phase of increasing and decreasing titers directly after they were inoculated.     

Variations in the immune response to natural Schistosoma mattheei infections in calves born to infected mothers

During previous work Schistosoma antibodies and circulating antigens were detected at birth in the serum from some calves born to Schistosoma mattheei infected mothers. The objectives of the present survey were: (1) to investigate the proportion of calves, born to cows infected with S. mattheei, which have specific antibodies and circulating schistosome antigens present in their serum at birth and (2) to investigate whether the presence or absence of these specific antibodies and/or circulating antigens at birth may affect the pattern of a natural S. mattheei infection in calves from 4 to 5 months of age, when the colostral antibodies are thought to be of negligible importance. A total of 28 calves born to infected mothers were randomly selected. Faeces, serum and colostrum samples were collected from the cows at calving, serum samples were collected from the calves at birth (day 0), after intake of colostrum (day 1) and monthly thereafter up to the age of 10 months. Both serum and colostrum samples were analysed for IgG(H+L) against SWAP mattheei and schistosome circulating anodic antigen (CAA) levels. The calves were exposed to a natural challenge from the age of 4-5 months. Faecal samples were collected from the calves monthly, starting at an age of 5 months up to 10 months, and were examined for faecal egg counts. Nine (group 1) out of the 28 calves were found to have specific antibodies in their serum at birth, in 5 of them CAA levels were also detected. In the other 19 calves (group 2) no IgG(H+L) or CAA were detected. At the end of the study faecal egg counts and CAA levels were significantly lower in calves from group 1 compared to group 2. Results confirm earlier work that specific antibodies and circulating antigens may be present in serum from calves at birth, and show that these calves have lower faecal egg counts and CAA levels after exposure to a natural challenge.     

Influence of dietary energy on follicular development, serum gonadotropins, and first postpartum ovulation in suckled beef cows

Twenty-eight Hereford x Angus cows (4 yr of age) were used to determine the effects of pre- and postpartum dietary energy on performance and reproductive function in suckled beef cows. The experiment was designed as a 2 x 2 factorial with cows receiving either 70 (L) or 150% (H) of NRC recommended level of dietary energy before and(or) after parturition, resulting in four treatment combinations (L-L, L-H, H-L, H-H). Prepartum diets were fed for approximately 110 d, and postpartum diets were fed until either 10 d after the second postpartum ovulation or 150 d postpartum for those cows that failed to ovulate. Cows receiving low compared with high levels of energy before calving lost more (P less than .01) weight, body condition, subcutaneous fat, and longissimus muscle area before parturition and had calves with lighter (P less than .01) birth weights. Cows receiving low compared with high levels of energy postpartum lost more (P less than .01) weight, body condition, and longissimus muscle area after parturition. Low levels of energy before and after parturition decreased (P less than .01) milk production and calf weight at 70 d of age. Rates of cervical and uterine involution were unaffected by dietary energy treatments. Cows receiving high levels of energy prepartum had increased (P less than .01) mean concentrations and pulse frequency of LH in serum after parturition, and cows receiving high levels of energy postpartum had increased (P less than .05) pulse frequency of LH. Low levels of energy postpartum decreased (P less than .01) appearance rate of small (5.0 to 7.9 mm) and large (greater than or equal to 10 mm) follicles, and low levels of energy prepartum decreased (P less than .02) appearance rate of large follicles based on transrectal ultrasonography. Cows receiving high levels of energy prepartum had shorter (P less than .02) intervals from parturition to ovulation, and a higher (P less than .01) percentage of the cows that received high levels of energy postpartum ovulated by 150 d postpartum. In summary, prepartum level of dietary energy influenced birth weight and weight gain of calves, milk production, concentrations and pulse frequency of LH in serum, appearance rate of large follicles, and the interval to first ovulation. Postpartum level of dietary energy influenced milk production, weight gain of calves, pulse frequency of LH, appearance rate of small and large follicles, and the percentage of cows that ovulated after parturition.     

Passive protection of calves against experimental infection with Salmonella typhimurium

Cows were vaccinated with formalin-killed Salmonella typhimurium approximately seven weeks and two weeks before parturition to investigate whether passive immunity could protect their calves against experimental S typhimurium infection. After birth the calves were left with their dam for 48 hours and then separated and fed cold, stored colostrum from their own dam for a further eight days. Oral challenge five days after birth with 10(8) S typhimurium did not result in the death of these calves even when they had absorbed little colostrum. Mortality was reduced to 22 per cent in calves which sucked from vaccinated dams and were then fed colostrum from unvaccinated cows and to 50 per cent in calves born to unvaccinated cows and later fed colostrum from vaccinated animals. Calves which sucked from a vaccinated dam and then received stored colostrum from the same cow excreted salmonellas for significantly shorter periods after challenge and were less often infected at necropsy 28 days after inoculation. Protection was not correlated with the levels of O or H agglutinating antibodies in serum, which were at a maximum 24 hours after sucking and then slowly declined. There was no evidence of an active antibody response in the serum. Measurement of the O and H response of cows after vaccination indicated that the vaccination schedule could be improved. The highest levels of agglutinating antibody were measured between two and three weeks after the first vaccination and there was only a minimal response to the second vaccination before parturition.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ultrasonographic evaluation of thymus in Holstein calves and Heifers and its diagnostic application

This study was performed to evaluate the cross section of the thymus in 46 clinically healthy Holstein calves and heifers from birth to 100 weeks of age and 8 age-matched affected animals with chronic bronchopneumonia by ultrasonography. The cross sectional area of the thymus increased in healthy calves and heifers from birth to 31 weeks of age, peaked around 35 weeks of age, and then decreased until 100 weeks after birth. A positive correlation (r = 0.74, P < 0.05) was found between the area in cross section and the weight of the whole thymus in calves and heifers with chronic bronchopneumonia. The cross- sectional areas of the thymus were significantly (P < 0.05) lowered in animals with chronic bronchopneumonia. The cross sections of thymus in clinically healthy calves at 2 weeks of age and heifers at 34 weeks and 87 weeks of age were hypoechoic, moderately hyperechoic and hyperechoic, respectively. The observation of thymus by ultrasonography seems to be an effective tool for estimating the size of the thymus objectively in Holstein calves and heifers from birth to 100 weeks of age. The results of this study prove the approach to be useful and applicable to monitor the growth of thymus in Holstein calves and heifers and their association with chronic pneumonia.     

Temporal changes in serum concentrations of acute phase proteins in newborn dairy calves

Age-dependent changes in blood concentrations of four bovine acute phase proteins (APPs), serum amyloid A (SAA), lipopolysaccharide binding protein (LBP), haptoglobin (Hp) and alpha(1)-acid glycoprotein (AGP), were examined using two groups of newborn dairy calves. APP concentrations were monitored for either 3 weeks (Group A, n=13) or 2 months (Group B, n=13) after birth. Blood was collected at day 0-1 (Group A only), day 3 and then once or twice weekly until the end of the study. The possible transfer of colostral SAA as a source of SAA in the offspring was investigated by determining SAA isoforms in the serum of calves and in colostrum of their dams. Serum concentrations of all four APPs were high after birth, and concentrations showed a gradual decrease during the first 3 weeks of life. The lowest concentrations were at 21 days of age, after which concentrations stabilized. The calves synthesized adult SAA isotypes, and circulating SAA was not derived from colostrum. The results indicated that post-partum elevation of APPs is associated with the birth process and/or factors in colostrum and not necessarily with disease-related processes. This stresses the importance of considering a calf's age when interpreting APP concentrations in serum.     

Risk of abortion associated with Neospora caninum during different lactations and evidence of congenital transmission in dairy cows

OBJECTIVE: To examine the relationship between exposure to Neospora caninum and abortion in dairy cows during their first, second, third, and fourth or later lactations and to establish the main mode of transmission in female calves from birth until their first pregnancy was terminated by abortion or parturition. DESIGN: Prospective observational study. ANIMALS: 460 Holstein cows and 79 female calves. PROCEDURE: Cows were classified as seropositive or seronegative to N caninum within 7 days after calving; incidence of abortion was compared between groups during different lactations. Blood samples were collected from female calves before ingestion of colostrum and every 6 months until their first pregnancy was terminated by abortion or parturition; number of seropositive calves was compared between seropositive and seronegative dams. RESULTS: During the first pregnancy of their second lactation, risk of abortion for seropositive cows was 2.8 times that of seronegative cows. Among 10 calves born to seropositive cows, 4 were classified as seropositive at birth and thereafter. Among 69 calves born to seronegative cows, all were classified as seronegative at birth; 67 calves remained seronegative thereafter. CONCLUSIONS AND CLINICAL RELEVANCE: Exposure to N caninum alone was not significantly associated with abortion in cows during the first, third, and fourth or later lactations. Seropositive cows that have aborted previously may have subsequent abortions attributable to N caninum. Congenital infection was the main mode of N caninum transmission in a cohort of female calves.