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1.  The effect of pre-enrichment on recovery of Streptococcus agalactiae, Staphylococcus aureus and mycoplasma from bovine milk. 
Epidemiology and Infection  1989;103(3):465-474.
The study was conducted to determine whether pre-enrichment would increase sensitivity of detecting Streptococcus (Str.) agalactiae, Staphylococcus (S.) aureus, and mycoplasma in bovine milk. Two procedures were followed, one involving direct inoculation of milk on bovine blood agar, and the other involving preenrichment in broth followed by inoculation on agar. Logistic regression was used to predict the probability of isolation as a function of culture procedure and two additional covariates, the California Mastitis Test (CMT) score of the milk and the type of sample (indicating sample storage temperature and herd mastitis status). A total of 13778 milk samples was cultured for each of the three bacteria. By using results of both direct inoculation and pre-enrichment, the probability of isolation compared to use of direct inoculation only and adjusted for effects of other variables was increased 3.6-fold for Str. agalactiae, 1.6-fold for S. aureus and 1.7-fold for mycoplasma. The probability of isolation for all three bacteria increased as the CMT score increased. For Str. agalactiae, there was a statistical interaction predicting that enrichment improved the odds of isolation more from milk with high CMT scores than from milk with low scores. Results indicate that pre-enrichment can substantially increase the sensitivity of bacteriological screening of dairy cows for mastitis caused by Str. agalactiae, S. aureus, and mycoplasma.
PMCID: PMC2249543  PMID: 2691266
2.  Effect of brucellosis vaccination and dehorning on transmission of bovine leukemia virus in heifers on a California dairy. 
Brucellosis vaccination and dehorning were examined for an association with bovine leukemia virus (BLV) infection in heifers on a California dairy between April 1984 and June 1987. Between December 1985 and June 1986, weaned heifers were dehorned using the gouge method at the time of brucellosis vaccination. Using logistic regression, the estimated probability for a nondehorned heifer to seroconvert within three months after brucellosis vaccination (0.08) was significantly less than that for heifers dehorned after a noninfected heifer (0.46) or than that for heifers dehorned after an infected heifer (0.85) (p = 0.039 and p less than 0.001, respectively). To evaluate risk of transmission by brucellosis vaccination, which was usually done within one month postweaning, cumulative proportions of heifers remaining uninfected were computed among heifers that did not seroconvert three months after dehorning. Because results of a Cox model analysis indicated that groups of heifers were 6.6 times more at risk of becoming infected if placed in pens holding gouge-dehorned heifers (where prevalence varied between 50 and 70%) (p less than 0.001) than other groups placed in pens without gouge-dehorned heifers (where prevalence varied between 10 and 30%), cumulative proportions of heifers remaining uninfected were computed for each type of group. The cumulative proportion of heifers remaining uninfected from weaning to first calving was 0.60 for the high prevalence group and 0.96 for the low prevalence group. No change in slope of cumulative proportions was observed before and after one month postweaning, suggesting that brucellosis vaccination was not an effective means of transmission.(ABSTRACT TRUNCATED AT 250 WORDS)
PMCID: PMC1255626  PMID: 2155048
3.  Protection of colostral antibodies against bovine leukemia virus infection in calves on a California dairy. 
A three-year prospective study involving 244 calves was undertaken on a California dairy to evaluate the protective role of colostral antibodies against bovine leukemia virus (BLV) infection in calves. Calves were followed from birth to the time they left their individual hutch (TLIH), at about 90 days of age. The probability of being infected at TLIH and the daily risk of infection between birth and TLIH were modelled using the logistic and the Cox models, respectively. Calves with no detectable antibodies during the first week of life were up to 2.00 and 2.75 times more likely to be infected at TLIH compared to calves with low and high concentrations of antibodies during the first week of life, respectively (p = 0.01). When the daily risk was modelled, calves without antibodies at the estimated day of infection were up to 3.4 and 11.6 times more likely to become infected than calves with low and high concentrations of antibodies on that day, respectively (p less than 0.001). Results indicated that calfhood infection may be reduced by about 45% through the feeding of colostrum with BLV antibodies. Further reduction in infection may be possible by feeding calves milk powder, milk replacer, and/or milk from noninfected cows. Results also indicated that quantification of the effect of a time-dependent risk factor, such as colostral antibody concentration, might be affected if treated as a fixed factor.
PMCID: PMC1255570  PMID: 2556213
4.  An epidemiological study of natural in utero infection with bovine leukemia virus. 
The purpose of this study was to examine rates of natural in utero infection with bovine leukemia virus for association with breed, sex, dam age, dam parity and time of maternal seroconversion. Analyses conducted for breed and sex, dam age and parity and time of maternal seroconversion were the FUNCAT procedure for categorical data, Wilcoxon Rank Sums test and Fisher's exact test, respectively. A total of 223 calves born between July 1979, and September 1980, to cows infected with bovine leukemia virus in the University of Florida Dairy Research Unit herd were tested for detectable bovine leukemia virus antibodies prior to the consumption of colostrum. Sera were tested for antibodies by agar-gel immunodiffusion and radioimmunoprecipitation using the glycoprotein-51 antigen. In a group of 125 calves in which in utero infection could be confirmed through serological follow-up (group A), eight calves (6.4%) had precolostral bovine leukemia virus antibodies. For all 223 calves (group B), 18 (8.1%) had detectable bovine leukemia virus antibodies. For calves in group A, no associations were detected between precolostral bovine leukemia virus antibodies and breed (p = 0.66), dam age (p = 0.86), dam parity (p = 0.83), or time of maternal seroconversion to bovine leukemia virus (p = 0.50). However, precolostral bovine leukemia virus antibodies were found in 17.4% of the males and 3.6% of the females in group A (p = 0.11) and in 12.4% of the males and 3.6% of the females in group B (p = 0.04).
PMCID: PMC1235945  PMID: 6315199
5.  Fall in antibody titer to bovine leukemia virus in the periparturient period. 
Twenty-seven cows with antibodies to bovine leukemia virus were bled before, during and after calving. All serum samples were tested quantitatively for bovine leukemia virus antibodies using both the agar-gel immunodiffusion test with a glycoprotein antigen and the radioimmunoprecipitation assay with an internal p24 protein antigen. A significant fall (P less than 0.001) in bovine leukemia virus-antibody titer was demonstrated with both tests at the time of calving, with a subsequent rise in antibody titer within one month of parturition. Bovine leukemia virus antibodies were not detectable using the agar-gel immunodiffusion test in two of these cows at the time of calving.
PMCID: PMC1320322  PMID: 6290013
6.  Congenital Neospora caninum infection in dairy cattle and associated calfhood mortality. 
A prospective cohort study was undertaken on two central California dairies, A and B, to estimate prevalence of congenital infection with Neospora caninum, to characterize temporal variation in prevalence, to determine if occurrence of congenital infection was associated with specific dam and calf attributes, and to estimate the effect of congenital infection on calfhood mortality. Of the 405 calves enrolled over a period of 2 1/2 y on dairy A and dairy B, 30.6% (85/278) and 53.5% (68/127), respectively, were seropositive precolostrally to N. caninum, as determined by an ELISA test. Adult cow seroprevalence at calving was 36.0% (82/228) for dairy A, and 57.9% (33/57) for dairy B. No evidence was found for a significant increasing or decreasing trend in adult and precolostral seroprevalence through the study period (P > or = 0.26). For both herds combined, 81% of seropositive cows (93/115) and 5% of seronegative cows (8/170) had congenitally infected calves. Seroprevalence did not increase with cow age on either dairy (P > or = 0.47). The probability of a calf being congenitally infected was not associated with dam age, dam lactation number, dam history of abortion, calf gender, or length of gestation (P > or = 0.11). High dam ELISA values at calving were significantly associated (P < or = 0.001) with an increased probability of congenital infection in her calf. Results of survival analyses of female calves available for follow-up indicated a consistently greater survivorship to 90 d in congenitally infected calves than in noninfected calves on both dairies, which was significant for dairy A (P = 0.07, n = 186) but not for dairy B (P = 0.69, n = 72), thus indicating that congenital infection does not necessarily have a detrimental effect on calf health. The findings of a similar magnitude in congenital infection rate and adult cow prevalence, the lack of increasing seroprevalence with cow age, the lack of an effect of dam age on precolostral seropositivity, and the constant seroprevalences during the study period, suggest that, in the two dairies studied, congenital transmission constituted a substantial amount of infection and was likely the major mode of transmission of N. caninum.
PMCID: PMC1263819  PMID: 8785719
7.  Effect of birthweight, total protein, serum IgG and packed cell volume on risk of neonatal diarrhea in calves on two California dairies. 
The objective of the study was to determine if there was a relationship between hematological, immunological and physiological variables of newborn calves and risk of diarrhea during the neonatal period. Four hundred and seventeen heifer calves from two dairies (A and B) in the San Joaquin Valley of California were enrolled at birth and scored daily, to 28 days of age, for evidence and severity of diarrhea (0 to 3). Calves were weighted at birth and blood sampled at two to five days of age to determine packed cell volume (PCV), total protein (TP) and IgG serum concentration. The Cox proportional hazards model was used to determine if age at onset of the first diarrhea episode and length of the first episode were associated with the hypothesized variables (PCV, TP, IgG and birthweight). The IgG concentration was not associated with the age at onset of diarrhea (p = 0.6052, Dairy A; p = 0.4393, Dairy B) but a high IgG concentration was associated with a decreased length of episode (p = 0.0325, Dairy A; p = 0.0912, Dairy B), particularly for calves born in the winter on dairy A (p = 0.0211). For calves born in the winter, those with either a high or a low birthweight had diarrhea at a younger age (p = 0.0102, Dairy A; p = 0.0020, Dairy B). Associations were also found for PCV and TP with both the age at onset and length of the first episode of diarrhea. Results suggest that parameters measurable at, or shortly after birth may have important prognostic value in evaluating risk of calf diarrhea.
PMCID: PMC1263635  PMID: 8269362
8.  Factors associated with in utero or periparturient transmission of bovine leukemia virus in calves on a California dairy. 
A three-year prospective study involving 143 calves born from infected cows was undertaken on a California dairy to evaluate possible factors of the dam associated with bovine leukemia virus infection in utero or during the periparturient period. In utero or periparturient infection occurred at a rate of 4.8% and was more likely in calves born to cows with an average peripheral blood lymphocyte count during pregnancy greater than 12,000 cells/microL (p = 0.043) or in calves born to cows that developed malignant lymphoma (p = 0.00004), but not in calves born to cows with p-24 antibodies (p = 0.675).
PMCID: PMC1263462  PMID: 1653640
9.  A method to estimate the somatic cell count of milk from a mastitic quarter using composite somatic cell count. 
The purpose of the study was to estimate the extent to which one quarter could be inflamed relative to the other three quarters of a cow, given that knowledge only of the composite milk somatic cell count (SCC) was available. An algebraic relationship, which incorporated the parameters of composite milk SCC, production loss associated with composite milk SSC, SCC of milk from an inflamed quarter, and SCC from three non-inflamed quarters, was used to derive hypothetical estimates of the SCC in one inflamed quarter. A simple case was considered in which one quarter was mastitic, the SCC in milk of the noninflamed quarters was equal, and there was no production compensation by the noninflamed quarters. Previously published estimates were used for production loss associated with composite milk SCC. For moderate composite milk SCC (300,000-500,000 cells/mL) and low-to-moderate SCC in milk of noninflamed quarters (100,000 cells/mL), the SCC of milk from one inflamed quarter was predicted to be very high, ranging from about 1.26 million (log10 SCC = 6.1) to 6.3 million (log10 SCC = 6.8) cells/mL, and compatible with signs of clinical mastitis. These results suggest that in order to screen cows with clinical mastitis in only one quarter, composite milk SCC should be considerably lower than values presented previously by other investigators.
PMCID: PMC1255627  PMID: 2306671
10.  Relationship between test-day measures of somatic cell count and milk production in California dairy cows. 
The relationship between test-day measures of milk somatic cell count and milk yield was evaluated using the November 1985 test data from 8352 Holstein cattle (2923 primiparous and 5429 multiparous cows) located in ten Tulare County, California dairies. Following correction for herd and stage of lactation effects, design variable regression was used to create separate models for primiparous and multiparous cows predicting the changes in milk production associated with milk somatic cell count class. Cell counts were stratified by 1/2 loge cell count (x1000 cells/mL) units, permitting comparisons with previous studies. Cell counts less than 148,000/mL were not found to be associated with significant reductions in milk yield when compared to the reference class (cell counts less than 20,000/mL). Consistent incremental decreases in milk production were not noted with increasing cell count strata, even following the natural log transformation. The most dramatic production losses were noted in the range of 148,000 to 665,000 cells/mL. Primiparous cattle in the 403,000 to 665,000 cell count strata experienced a 5.22 kg (19.72%) decrease in test-day milk yield. Multiparous cattle in the same class experienced 3.01 kg (7.82%) reductions in milk production. Primiparous and multiparous cows had similar production losses. The study population differed from previous studies on the basis of herd size, milk production and the level of udder health, measured by milk somatic cell count. These differences and the choice of experimental design may in part explain differences in study results and conclusions.
PMCID: PMC1255545  PMID: 2713782

Results 1-10 (10)