Analysis of hepatic enzyme activities in serum samples from 1- to 3-day-old pups revealed alkaline phosphatase (ALP) activities that were 30 times higher and gamma-glutamyltransferase (GGT) activities that were 100 times higher than activities in clinically normal adult dogs. A study was conducted to investigate high enzyme activity in pups and to determine whether there is any association between serum enzyme activity and colostrum ingestion, passive transfer of maternal serum enzyme (in colostrum or in utero), or excessive renal or hepatic tissue enzymes. Serum enzyme activity was quantified in 15 neonatal pups before and after ingestion of colostrum and in 3 colostrum-deprived neonates fed a milk substitute. Serum samples were collected on postpartum days 0, 1, 10, 15, and 30. Enzyme activity was also quantified in serum from pregnant and lactating bitches (collected on days - 2, 0, 1, 10, 30), hepatic and renal tissue from clinically normal adult dogs and 1-day-old pups, colostrum, milk (collected on days 10 and 30), and milk replacer. Significant (P < 0.01) differences in serum GGT and ALP activities between colostrum-deprived and suckling pups did not exist before initial feeding. Significant (P < 0.001) increases in serum GGT and ALP activities developed within 24 hours in suckling pups, but not in the colostrum-deprived pups. At 10 and 30 days after birth, serum GGT and ALP activities were less than values before suckling in all pups. Enzyme activities in bitches' serum remained within the normal range for adult dogs throughout whelping and lactation. Renal GGT and ALP activities were substantially greater than hepatic enzyme activities in neonates and adults. Renal tissue from adults contained 3 times greater GGT and 2 times greater ALP activities than that from neonates. Hepatic tissue from neonates contained 5 times more GGT activity than did hepatic tissues from clinically normal adults; however, hepatic ALP activity was similar in adults and neonates. Colostrum and milk bad substantially higher enzyme activities than did bitches' serum. Activities of GGT and ALP in milk were 100 times and 10 times greater, respectively, than activities in serum through day 10. By day 30, GGT and ALP activities in milk were less than before suckling. Enzyme activity was not detected in the milk substitute. These studies reveal an association between colostrum ingestion by suckling and acute, profound increases in serum GGT and ALP in 1- to 3-day-old pups. Although this phenomenon might be useful as an indicator of colostrum ingestion, it precludes the diagnostic use of either enzyme as an indicator of hepatobiliary disease in 3-day-old pups.

The relative sensitivity of bovine blood monocytes and macrophages isolated from milk to lipopolysaccharide, with respect to interleukin 1 (IL-1) production, was evaluated. Addition of lipopolysaccharide (0 to 30 microgram/ml) to theculture medium resulted in increases in secreted and intra-cellular IL-1 activity for monocytes and milk macrophages, with maximal stimulation achieved at 30 microgram oflipopolysaccharide/ml of medium. At this concentration of lipopolysaccharide, monocytes released 76% of the total IL-1, whereas milk macrophages released only 26% of the total IL-1 produced within the cell. Secretion of a small quantity of IL-1 was a common property of macrophages isolated from healthy and mastitic quarters. We concluded that limited secretion of IL-1 may render the milk macrophages less efficient in promoting lymphocyte activation.

Hydrated sodium calcium aluminosilicate (HSCAS), an anticaking agent for agricultural feeds, was added to aflatoxin (AF)-contaminated diets of 3 lactating dairy cows and evaluated for its potential to reduce aflatoxin M1 (AFM1) residues in milk. During phase I, cows were fed alternating diets that consisted of 200 microgram of AF/kg of feed for 7 days, 0.5% HSCAS plus 200 microgram of AF/kg of feed for 7 days, and feed with the HSCAS removed for a final 7 days. The AFM1 milk concentrations from the intervals with HSCAS added to diets were compared with those times when HSCAS was absent. The presence of 0.5% HSCAS in feed containing 200 microgram of AF/kg reduced AFM1 secretion into the milk by an average of 0.44 microgram/L (from pretreatment of 1.85 microgram/L to 1.41 microgram/L with HSCAS, a 24% reduction). Following a 10-day period of noncontaminated feed consumption and no AFM1 residues in the milk, phase II of the study was begun. The same experimental design as phase I was used, but the dosages of HSCAS and AF were changed to 1.0% and 100 microgram/kg of feed, respectively. The addition of 1.0% HSCAS in feed containing 100 microgram of AF/kg decreased AFM1 content in the milk by an average of 0.40 microgram/L (from a pretreatment of 0.91 microgram/L to 0.51 microgram/L when HSCAS was present, a 44% reduction). These findings suggest that HSCAS, a high-affinity sorbent compound for AF in vitro, is capable of reducing the secretion of AFM1 into milk.

To compare the effects of milk stasis and milk flow on Brucella abortus infection of the mammary gland under the same systemic conditions, primiparous goats (n = 5) were inoculated IV with B abortus on the day of parturition, and suckling by their neonates was restricted to one mammary gland. Goats were euthanatized and necropsied at 3 weeks after inoculation, and milk, mammary glands, and supramammary lymph nodes were evaluated by bacteriologic, histologic, and immunoenzymatic staining techniques. Nonnursed mammary glands had high titers of brucellae in milk, moderate interstitial mastitis, and brucellar antigen in macrophages located primarily in alveolar and ductal lumina. Brucellae often filled the macrophage cytoplasm. In contrast, nursed mammary glands had fewer brucellae in milk, minimal inflammatory changes, and no detectable brucellar antigen in histologic sections. Hyperplastic changes were only seen in supramammary lymph nodes draining nonnursed mammary glands; these contained more brucellae than lymph nodes draining nursed mammary glands. These studies show that milk stasis may be the sole cause of increased susceptibility of nonnursed mammary glands to B abortus infection.

A flow cytometric procedure was evaluated to measure the oxidative burst activity (hydrogen peroxide formation) of bovine neutrophils. The method involves measuring the oxidation of intracellular dichlorofluorescin to fluorescent dichlorofluorescein (DCF). Phorbol myristate acetate (PMA) was used to perturb the neutrophil plasma membrane. The sources of variation introduced into the DCF assay were also examined. The sources of variation were attributable to the isolation of neutrophils from blood, variation between duplicate assays and duplicate flow cytometric determinations of oxidative product formation, variation in neutrophil oxidative product formation among cows, and the variation (over repeated daily and weekly neutrophil isolations) in neutrophil oxidative product formation. A final objective was to determine effects of dexamethasone on oxidative product formation, and whether differences existed between blood and mammary neutrophils in oxidative product formation. There was an increasing trend in the formation of DCF with increasing time of incubation and with increasing PMA concentration. Increasing the concentration of PMA decreased lag time and increased the rate of oxidative product formation. The increase in DCF formation was statistically significant up to a PMA concentration of 10 ng/ml. This concentration was considered optimal for bovine neutrophils. Examination of the sources of variation indicated that (i) the neutrophil isolation technique was a major source of variation (17.2 to 28.4% of the total variation), and that more than one neutrophil isolation within a cow would be required to obtain an accurate estimation of DCF formation in neutrophils; (ii) duplicate assays and duplicate readings on the flow cytometer accounted for < 0.05% of the total variation and would not be necessary when performing the DCF assay; (iii) large variation (62.4 to 70.8%) existed among cows in neutrophil oxidative product formation, indicating that any treatment being compared should be done either within or preferably repeated across a large number of cows; and (iv) the variation over repeated daily (0.3%), but not weekly (19.6%) determinations of neutrophil oxidative product formation, were small enough to allow for the evaluation of major physiologic and environmental effects. Intramuscular administration of dexamethasone (50 microgram/ kg of body weight) resulted in an approximate 80% decrease in neutrophil oxidative product formation. Oxidative product formation was 75% less for neutrophils isolated from mammary secretions when compared with neutrophils from blood. These results indicated that the DCF procedure was responsive to factors known to interfere with oxidative metabolism of bovine neutrophils.

Milk samples were collected at onset of 508 episodes of clinical mastitis on a 1,700-cow dairy farm in Michigan. Daily milk production and disease events were recorded for all cows in the herd. Despite statistical association with severity of mastitis, this association was too weak for N-acetyl-beta-D-glucosaminidase (NAGase) activity to be of great value as a prognostic test for clinical mastitis. High milk NAGase activity was significantly (P < 0.0001) associated with: increased duration of treatment; increased duration of clinical signs of mastitis; decreased daily milk production; and increased risk of the cow being culled because of mastitis. The NAGase value was combined with days in milk production, baseline milk production before mastitis onset, parity, and season of onset to predict the outcome of clinical cases as measured by the first 3 aforementioned variables. Statistical models explained little of the variability among cows in duration of treatment (R2 = 0.11), duration of clinical signs of infection (R2 = 0.11), and milk production change (R2 = 0.09).

Log-linear methodology was used to examine relations among caprine arthritis-encephalitis virus (CAEV) seroreactivity and host/management factors in a cross-sectional study of 2,826 goats on 13 California dairies. The CAEV serologic status was associated with age and feeding method (pasteurized/unpasteurized milk), but not with breed. Data from a prevalence survey of 321 goats from 2 additional dairies demonstrated very good fit of the selected log-linear model (P = 1.00), indicating that the model was very appropriate to describe the relations. Odds of seropositivity and odds ratios were generated by use of a logit model derived from the log-linear model. Goats raised by the unpasteurized feeding method were estimated to have been 3.3 times more likely to be CAEV-seropositive than goats fed by the pasteurized method, when adjusted for the effects of age. Goats aged 2, 3, 4, and 5 or greater years were estimated to have been 1.7, 2.6, 4.5, and 5.7 times, respectively, more likely to be CAEV-seropositive than were yearling goats when ratios were adjusted for pasteurization status. Breed, gender, and herd of origin were not associated with CAEV seroreactivity when the effects of other factors were considered. Estimated odds of CAEV seroreactivity and the associated odds ratios for combinations of factor levels are reported. In this study, the magnitude and direction of the associations among CAEV serologic status, age, and pasteurized feeding methods were demonstrated.

The purpose of this study was to evaluate the effect of withdrawal of lactose from the diet for 72 hours on lactase activity in the jejunal mucosa of conventionally raised calves. The descending portion of the duodenum of six Holstein calves < 24 hours old was cannulated. The calves were fed milk except on days 5, 6 and 7 when they were given the same volume of an electrolyte solution. Sequential biopsy specimens of the proximal jejunal mucosa were obtained for three weeks and the lactase activity determined. Lactase activity was highest on day 1 and a trend toward decreased lactase activity from birth until three weeks was observed. Mean lactase activity was significantly (p < 0.05) higher for days 1, and 3 compared to days 9, 13 and 17. The withdrawal of milk and replacement by an electrolyte solution during three days had no significant effect on jejunal mucosal lactase activity in neonatal calves.

The type of plasminogen activator (PA) produced by bovine milk macrophages has been determined. Macrophages produce a PA protein with molecular weight of 28,000 and isoelectic point of 8.5, and with enzymatic activity independent of fibrin. These characteristics are identical to those reported for bovine urokinase-PA. Although blood monocytes and milk macrophages produce PA after stimulation with lipopolysaccharide, mammary macrophages are clearly limited in their ability to release PA. At maximal stimulation, 78% of the PA produced by milk macrophages remained cell-associated. In marked contrast, blood monocytes released 76% of the PA produced into the culture medium. Macrophages isolated from mastitic quarters produced higher (2.5 times) amounts of PA, compared with those produced by macrophages isolated from healthy quarters. However, in both cases, macrophages were unable to secrete the protein already produced. The limited PA secretion by milk macrophages might be a residual function of a differentiated macrophage population.

Polymorphonuclear cells have a critical role in the pathogenesis of bovine mastitis. We have documented that experimentally induced Staphylococcus aureus mastitis is associated with cyclic increase and decrease in the quantity of viable bacteria shed in the milk. Concomitant with this cycling of bacteria is an inverse cycling of the hosts cells within the milk. Such somatic cells were determined to be greater than or equal to 95% polymorphonuclear cells. The quality of these cells was evaluated by measuring their relative efficiency of bacterial killing and phagocytosis at various times during an infection. Host polymorphonuclear cells had as much as 10,000-fold variation in the bactericidal failure rate for staphylococci during cell cycling. The most efficient bactericidal effect was observed at or near the peak of the somatic cell count (SCC). The ability of these cycling cells to ingest fluorescent beads was also quantitated by use of flow cytometry. The percentage of phagocytic polymorphonuclear cells that ingested fluorescent latex beads ranged from 15 to 80% of the total cell population during cell cycling, and tended to be optimal at or near peak SCC. In addition, the average number of beads ingested varied between 1 and 2 particles/polymorphonuclear cell, with as many as 17% of the phagocytic cells ingesting 4 or more beads at maximal efficiency. Polymorphonuclear cells from quarters infected with S aureus varied quantitatively (total SCC) and qualitatively (bactericidal activity and phagocytic ability) during the course of an infection. Not only is the quantity of host's phagocytic cells in the mammary gland central to the defense mechanism against infection, but the biological activation state appears to be equally important. The role of these cells in the pathogenesis of a cycling infection is presented in a model to explain the cyclic nature of mastitis.