Relationship among specific bacterial counts and total bacterial and somatic cell counts and factors influencing their variation in ovine bulk tank milk.

To analyze the relationship among the counts of different organisms and total bacterial count (BTTBC) and somatic cell count (BTSCC) as determined in dairy laboratories in ovine bulk tank milk, 751 bulk tank milk samples from 205 dairy sheep flocks belonging to Consortium for Ovine Promotion (CPO) were collected between January and December 2011. Four samplings were carried out in each flock, once per season, throughout 1 yr. Variables analyzed were bulk tank counts of thermoduric, psychrotrophic, coliform, and gram-positive catalase-negative cocci (GPCNC) bacterial groups. Thermoduric, psychrotrophic, and coliform species were significantly related to BTTBC, whereas GPCNC were correlated with both BTTBC and BTSCC variables. Highest counts were for psychrotroph and coliform groups, and a moderate to high correlation (r=0.51) was found between both variables, indicating that poor cleaning practices in the flocks tend to select for less-resistant organisms, such as gram-negative rods. In addition, BTTBC correlated with BTSCC (r=0.42). Some variation factors for specific bacterial counts, such as breed, season, milking type, dry therapy, and milk yield, were also analyzed. Flock information was collected from flock books, annual audits, and the CPO traceability system. Psychrotrophs and coliforms had elevated counts in winter, whereas GPCNC were higher in summer and in hand-milked flocks. Dry therapy contributed to the reduction in psychrotrophic bacteria; therefore, some strains of mammary pathogens could also be psychrotrophic bacteria. Results of this study would be helpful for troubleshooting milk quality problems and developing premium payment systems in dairy sheep.

Characterization of coagulase-positive staphylococci isolated from tank and silo ewe milk.

The prevalence of coagulase-positive staphylococci (CPS) was studied among 390 samples of ewe milk. Fifty-seven (14.85%) samples of tank milk and all samples (6) of silo milk gave a positive result on Baird-Parker agar base supplemented with rabbit plasma fibrinogen, whereas amplification of the coagulase (coa) gene was successful in 6 (1.56%) samples of tank milk and in all silo samples. Phenotypic and genetic analysis of 153 isolates identified 151 (98.69%) as Staphylococcus aureus. Amplification of the coa gene was positive for 149 isolates (97.39%). The staphylococcal enterotoxin (SE) C gene was detected in 116 strains (75.82%), whereas more than one SE gene was carried in 5 strains (3.26%). None of the isolates harbored the genes for SEE or for methicillin resistance. A high prevalence of CPS carrying enterotoxin genes should be of concern because ewe milk is mainly processed into raw milk cheeses. The detection of the coa gene from milk samples could help to assess the microbiological safety of raw milk intended for direct use in the dairy industry.

Short communication: effect of dry therapy using an intramammary infusion on bulk tank somatic cell count in sheep.

A total of 3,141 records of bulk tank milk somatic cell counts (BTSCC) and bulk tank milk total bacterial counts (BTTBC) were obtained over 24 mo from 25 dairy flocks of Assaf ewes belonging to the Consortium for Ovine Promotion in Castilla-León, Spain, in which a complete dry therapy program was carried out in 10,313 ewes using an antibiotic infusion containing 100 mg of penethamate hydriodide, 280 mg of benethamine penicillin, and 100 mg of framycetin sulfate. The selection criteria for all flocks were BTSCC mean values > or =1,000 x 10(3) cells/mL and absence of dry therapy before the start of this experiment. Significant effects on log BTSCC were detected for treatment, milking system, flock within milking system, month within flock by treatment, the interactions treatment by milking system and flock by treatment within milking system, and log BTTBC. After dry therapy was implemented, log BTSCC decreased significantly in machine-milked flocks (5.95 +/- 0.007) compared with values before antibiotic treatment (6.13 +/- 0.008). The effect was observed at the beginning of the second lactation posttreatment (5.98 +/- 0.013). However, dry therapy was not effective in hand-milked flocks, suggesting poor hygiene conditions. A significant relationship was found between BTSCC and BTTBC; therefore, programs for improving milk hygiene should be implemented for both BTSCC and BTTBC variables at the same time.

Influence of an intramammary infusion at drying-off of combined penethamate hydriodide, benethamine penicillin, and framycetin sulfate on intramammary infections and somatic cell counts in dairy sheep.

The dynamics of intramammary infection (IMI) during the dry period were studied in 435 half-udders of 229 Assaf ewes, belonging to 2 flocks with high and medium IMI prevalences. Ewes were randomly assigned to 2 lots: 1) treated lot (TL) with 223 half-udders (118 ewes), which received complete dry therapy (1 syringe/teat) of an antibiotic combination containing 100 mg of penethamate hydriodide, 280 mg of benethamine penicillin, and 100 mg of framycetin sulfate, and 2) control lot (CL) with 212 nontreated half-udders (111 ewes). Two samplings per half-udder were carried out on 2 different days in the 5 d preceding drying-off, and 2 other samplings were again carried out in the 5 first d of the postpartum period. The length of the dry period averaged 109.0 d. Cure, persistent infections, reinfection, and new infection rates were 81.7, 12.8, 5.5, and 7.9%, respectively, for TL and 13.3, 70.4, 16.3, and 22.8%, respectively, for the CL. The prevalence of IMI decreased significantly from 48.9% at drying-off to 13.0% at lambing for the TL, but it did not vary for the CL (46.2 and 52.4%, respectively). Within the TL, IMI prevalence significantly diminished for Staphylococcus (41.3 to 9.9%) and Streptococcus (5.8 to 1.8%) genera, and more specifically this decrease was most evident for Staphylococcus epidermidis and Streptococcus agalactiae species. Log somatic cell count (SCC) diminished significantly between drying-off (5.68) and lambing (5.33) in the TL, whereas log SCC did not vary in the CL (5.61 vs. 5.66). This SCC reduction was very significant in the flock with the greater IMI prevalence. As a conclusion, the antibiotic formulation used as dry therapy drastically diminished IMI prevalence and SCC during the dry period in dairy ewes as a result of greater IMI cure rates and lower reinfection and new infection rates in the TL compared with the CL.

Short communication: Evaluation of the overall accuracy of the DeLaval cell counter for somatic cell count in ovine milk: effect of soak time in diluted and undiluted milk samples.

This study evaluated the performance of the DeLaval cell counter (DCC) when analyzing ovine milk with different soak times (defined as the permanence time of samples within the DCC cassette before starting the DCC counting procedure) in diluted and undiluted milk samples in 2 dairy sheep breeds. A total of 101 composite ovine milk samples (50 from Assaf ewes and 51 from Churra ewes), ranging between 50 x 10(3) and 2,200 x 10(3) cells/mL, were divided into 10 aliquots/milk to be analyzed by DCC. Four undiluted aliquots and 4 aliquots diluted 1:1 in PBS were analyzed by using soak times of 0, 1, 2, and 3 min/aliquot, and the other 2 aliquots were diluted 1:1 in propidium iodide or ethidium bromide staining solutions and analyzed by DCC. Milk samples were also analyzed by the Fossomatic method, as a reference. All analyses were carried out in duplicate. Undiluted milk samples with soak times >or=1 min showed large coefficients of regression (b = 0.96 to 0.98) and correlation (r > 0.99) when compared with the Fossomatic method. In these samples, DCC gave repeatability standard deviations (s(r) = 35 to 51 x 10(3) cells/mL) lower than other DCC analytical conditions (s(r) = 49 to 74 x 10(3) cells/mL), and their log SCC means (5.51 to 5.52) were close to the reference value (5.56). The log SCC means corresponding to samples diluted 1:1 in staining solutions (5.55) did not differ from the reference value; however, these aliquots had lower regression coefficients (b: 0.92 to 0.93). Samples diluted 1:1 in PBS and undiluted samples with a 0-min soak time showed a global accuracy similar to or lower than undiluted samples with soak times >or=1 min. Breed did not seem to affect the results. We concluded that undiluted raw milk with a soak time >or=1 min and analyzed by DCC shows suitable overall accuracy in ovine milk compared with the reference method and can be considered as the best option for on-farm use from an operational point of view.

Performance of blue-yellow screening test for antimicrobial detection in ovine milk.

Drug residues in milk are important because of public health and industrial implications. The detection limits of 25 antimicrobial agents were determined by the blue-yellow screening method in ovine milk. For each drug, 8 concentrations were tested on 20 ovine milk samples from individual ewes in midlactation. Detection limits determined by means of logistic regression were below European Union maximum residue limits (EU-MRL) for penicillin G (3 to 4 microg/kg), ceftiofur (96 to 107 microg/kg), framycetin (720 to 781 microg/kg), neomycin (915 to 1,084 microg/kg), and tylosin (44 to 51 microg/kg). Detection limits for ampicillin (5 to 6 microg/kg), cloxacillin (33 to 42 microg/kg), cefoperazone (73 to 82 microg/kg), cefalexin (160 to 202 microg/kg), gentamycin (355 to 382 microg/kg), streptomycin (3,063 to 3,593 microg/kg), tilmicosin (109 to 131 microg/kg), erythromycin (444 to 522 microg/kg), spyramicin (1,106 to 1,346 microg/kg), sulfadimethoxine (101 to 119 microg/kg), sulfathiazole (122 to 151 microg/kg), sulfamethazine (309 to 328 microg/kg), sulfanilamide (1,750 to 2,674 microg/kg), tetracycline (233 to 257 microg/kg), oxytetracycline (398 to 501 microg/kg), doxycycline (323 to 419 microg/kg), chlortetracycline (3,331 to 3,989 microg/kg), danofloxacin (4.7 to 5.5 mg/kg), enrofloxacin (41 to 46 mg/kg), and flumequin (63 to 71 mg/kg) were higher than the EU-MRL. Although the blue-yellow method showed improved sensitivity compared with other tests studied in ovine milk, the performance of screening methods for detecting antimicrobial agents in milk of this species should be improved.

Evaluation of the overall accuracy of the DeLaval cell counter for somatic cell counts in ovine milk.

The DeLaval cell counter (DCC) is a portable device designed for on-farm somatic cell count (SCC) analysis in bovine milk. This study evaluated the performance of the DCC when analyzing ovine milk. A total of 29 composite ovine milk samples, ranging between 20 x 10(3) and 2,200 x 10(3) cells/mL, were divided into 15 aliquots/milk sample corresponding to 5 SCC methods using 3 types of preservation (unpreserved, azidiol, and bronopol). The SCC methods were the Fossomatic (FSCC), the DCC in undiluted samples, and the DCC in samples diluted 1:1 in 3 different types of diluents (PBS + Triton X-100, PBS + ethidium bromide + Triton X-100, and PBS + propidium iodide + Triton X-100). All analyses were carried out in duplicate. In addition, each sample was analyzed in quadruplicate by the direct microscopic method (DMSCC) using Pyronin Y-methyl green as a stain. Comparison of methods was based on overall accuracy studies (means comparison, repeatability, and regression studies vs. DMSCC and FSCC as reference methods). The DCC methods used to analyze milk samples diluted in staining solution (with ethidium bromide or propidium iodide) showed large coefficients of regression (b = 0.91 to 1.01) and correlation (r > 0.99) when compared with the DMSCC and FSCC methods. In these samples the DCC gave repeatability values (s(r) = 33 to 48 x 10(3) cells/mL) similar to the DMSCC (s(r) = 36 x 10(3) cells/mL), and their log SCC means (5.52 to 5.54) did not differ from the reference value (5.54). However, undiluted samples analyzed by the DCC method showed large standard deviations of repeatability and SCC values lower than those by the DMSCC or FSCC methods, probably because of the high solids content in ovine milk. The type of preservation did not affect the outcomes. Consequently, the DCC was determined to be accurate when analyzing diluted ovine milk based on comparison with the SCC reference methods.