Diet and cooling interactions on physiological responses of grazing dairy cows, milk production and composition.

The objective of this trial was to evaluate the effects of diet and cooling in the holding pen before milking on rectal temperature, respiration rate and milk production and composition. Fifty-eight lactating Holstein cows were used in a factorial split-plot design, at Rafaela Experimental Station from 12 January to 3 March 2003. The treatments were combinations of two diets: control (CD) and balanced (BD) with two levels of cooling before milking: none (NSF) and a sprinkler and fans (SF). Forage:concentrate ratios for CD and BD were 81:19 and 68:32, respectively. Cows were milked twice daily. Milk production was recorded daily, and milk composition (fat, protein, lactose and urea) was analysed twice a week. The physiological data were recorded once a week, before the cattle entered the holding pen and after milking, in the afternoon. Average maximum weekly temperature humidity index was 75.4 and ranged from 61.4 to 83. There were highly significant effects of cooling on physiological responses. Milk production was affected by diet and cooling, with no interaction; the highest and lowest production of milk was 22.42 and 20.07 l/cow per day, for BD+SF and CD+NSF, respectively. Protein was affected by diet, and was higher for BD (3.17 vs. 3.08%). There were interaction effects on milk fat at the 8% level, the highest concentration being 3.65% for BD+NFS. It was concluded that under grazing conditions, cooling by sprinkler and fans before milking improves the comfort of dairy cows, and that the effects on milk production and composition are enhanced when diets are specially formulated for heat-stress periods.

Fluorescence polarization assay for the diagnosis of bovine brucellosis: adaptation to field use.

A fluorescence polarization assay (FPA) was used to test whole blood samples prepared by mixing blood cells from cattle without exposure to Brucella abortus (B. abortus) with sera from animals with confirmed (bacteriologically) infection. A cut-off value between negative and positive values was initially established to be 87.2mP. This value was changed to 95mP to increase assay specificity without loss of sensitivity when testing blood samples from negative animals. The FPA technology was applied to whole blood samples in the field and to stored whole blood samples using two diluent buffers. Relative sensitivity and specificity values for the FPA performed in the field, based on buffered antigen plate agglutination test and competitive enzyme immunoassay results were 95.3 and 97.3%, respectively. However, to obtain maximum sensitivity and specificity, a cut-off value of 105mP was determined for fresh whole blood samples. The relative sensitivity and specificity values of the FPA when testing stored whole blood samples were 100% each using a 95mP cut-off.The usefulness of the FPA for testing whole blood samples in the field was demonstrated.

Use of Brucella abortus vaccine strain RB51 in pregnant cows after calfhood vaccination with strain 19 in Argentina.

One hundred and seven pregnant cows, which had been calfhood vaccinated with Brucella abortus strain 19 (S-19) were revaccinated with either S-19 or strain RB51 (S-RB51). All S-19-revaccinated animals seroconverted, while none of the RB51-revaccinated animals seroconverted. Two out of 25 (8%) S-19-revaccinated animals aborted, while none of the 57 RB51-revaccinated group aborted. Four of the S-19-revaccinated animals shed S-19 in the milk for at least 7 days, while only 1 cow shed S-RB51 for at least 3 days (but <7 days) post-parturition. Revaccination of strain 19 calfhood-vaccinated, pregnant cattle with S-RB51 appears to be a safe procedure with no diagnostically negative consequences.

Validation of enzyme-linked immunosorbent assays for the diagnosis of bovine brucellosis.

The purpose of this study was to evaluate the performance of the indirect enzyme immunoassay (IELISA) and the competitive enzyme immunoassay (CELISA) for the diagnosis of bovine brucellosis in comparison to conventional serological tests routinely used in Argentina. Serum samples (n = 3500), from Brucella-free herds, from vaccinated cattle and from naturally infected cattle, were tested by the following tests: buffered antigen agglutination test (BPAT), rose bengal test (RBT), 2-mercaptoethanol test (2-ME), complement fixation test (CFT), IELISA and CELISA. Sensitivity and specificity of the BPAT, RBT, IELISA and CELISA were determined relative to the 2-ME and the CFT. The CELISA was considered suitable for eliminating most serological reactions of vaccinated animals and was more specific than the other tests. The results indicate the potential use of the CELISA as a complementary assay in the brucellosis control and eradication program in Argentina and other countries, where Brucella abortusstrain 19 vaccination is mandatory.

Fluorescence polarization assay: application to the diagnosis of bovine brucellosis in Argentina.

A homogeneous fluorescence polarization assay (FPIA) for detection of bovine antibody to Brucella abortus was validated in Argentina Sera were defined based on their reactivity in the buffered antigen plate agglutination test (BPAT) and the competitive enzyme immunoassay (CELISA). Sera negative in these tests were collected from farms without evidence of brucellosis (n=733). Sera positive in the two tests were collected from cattle on farms from which B. abortus was isolated from at least one animal (n=1039). Sera from cattle vaccinated 26, 89, 240 and 272 days previously with B. abortus strain 19 were collected and tested. A cut-off value of 87 mP was determined for the FPIA, resulting in relative sensitivity and specificity values of 98.1 and 99.6%. The specificity for B. abortus strain 19 vaccinated cattle was 64.9% (26 days post vaccination, DPV), 92.1% (89 DPV), 98.6% (242 DPV) and 97.1% (272 DPV). These values were compared to those obtained with the BPAT, the CELISA, the indirect ELISA, the complement fixation test and the 2-mercaptoethanol agglutination test. Sera from 18 cattle which were vaccinated and revaccinated with B. abortus strain 19 were also tested by the same assays and the FPIA was found to be 100% specific. The use of the FPIA as a diagnostic test for brucellosis is discussed.

Comparative performance of the enzyme-linked immunosorbent assay (ELISA) and conventional assays in the diagnosis of bovine brucellosis in Argentina.

The FAO/IAEA enzyme-linked immunosorbent assay (ELISA) kit for the diagnosis of bovine brucellosis was compared in Argentina with two screening tests, the Rose Bengal (RB) and the buffered plate antigen (BPA) agglutination tests and with two confirmatory tests, the 2-mercaptoethanol (2-ME) agglutination and the complement fixation (CF) tests. In the testing of Brucella abortus Strain 19 (S19) vaccinated cattle from Brucella-free dairy herds, the diagnostic specificity estimate of the ELISA (99.7%) was shown to be comparable to the RB (99.7%), 2-ME (99.8%) and CF (99.9%) and greater than the BPA (90.6%). In the testing of S19 vaccinated cattle from infected herds, the sensitivity estimates of the BPA (99.5%, 99.6% and 98.6% respectively) relative to CF,2-ME and ELISA positive reactors were comparable and high. The relative sensitivity estimates of the RB (86.3%, 81.4% and 79.1%) in the same comparison were disparate and lower. The ELISA demonstrated the highest relative sensitivity estimates (97.1% and 95.2% respectively) in a three-way comparison between ELISA, CF and 2-ME positive reactors from these herds. Relative to BPA positive reactors from the same infected herds, the sensitivity estimate of the ELISA (57.0%) was comparable to the 2-ME (56.2%) and higher than the CF (51.8%). These results would suggest that the overall diagnostic specificity and sensitivity of the ELISA test is comparable, if not superior, to the tests used to confirm BPA positive reactor status.