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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 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
3.  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

Results 1-3 (3)