C. Gonzalo

Factors influencing variation of fatty acid content in ovine milk

Between January 2006 and December 2007, a total of 4,579 test-day observations for contents of milk fatty acids (FA) were obtained from 2,218 lactations of 1,109 ewes belonging to 14 Churra dairy flocks. The 36 analyzed FA were quantified as grams per 100 g of total FA and were grouped as 18 dependent variables: 10 FA, 6 groups of FA, and 2 FA indexes. Flock, day of testing within flock (TD), ewe age, stage of lactation, and season effects contributed significantly to variations in FA. The 2 most important variation factors were flock (3 to 30% of total variance) and TD (35 to 70% of total variance). The percentage of variance explained by the TD effect for conjugated linoleic acid (CLA, C18:2 cis-9, trans-11) and linolenic acid (C18:3 cis-9, cis-12, cis-15) was particularly high: 60.7 and 68.2%, respectively. The season effect was also a very important variation factor, closely linked to feeding. The most significant seasonal variations were observed in polyunsaturated FA, with the highest values occurring in spring and summer and the lowest in winter. More specifically, CLA and linolenic acid contents were 44 and 30% higher in spring-summer than in winter. As the age of the ewe increased, the monounsaturated and polyunsaturated FA decreased and the short- and medium-chain saturated FA increased. The CLA and the CLA/C18:1 trans-11 Delta(9)-desaturase index increased significantly throughout lactation. The correlation coefficient between rumenic acid (CLA) and vaccenic acid was high (0.47) because of the precursor-product relationship via the Delta(9)-desaturase enzyme. The correlation coefficients were high between C10:0 and C12:0 (0.79), C12:0 and C14:0 (0.73), and C14:0 and C16:0 (0.29), probably because of their similar metabolic origin. Positive correlations were also obtained among the C(18) FA family. All the studied factors of FA variation would be considered as fixed effects in the statistical models used for estimation of genetic and phenotypic parameters from test-day records of commercial flocks.

Effects of selective and complete dry therapy on prevalence of intramammary infection and on milk yield in the subsequent lactation in dairy ewes

The study was carried out in a commercial flock on 286 Churra breed ewes (566 half-udders) assigned to three lots depending on the type of antibiotic dry therapy received in the lactation previous to the one studied. One-hundred-and-four ewes were given complete therapy in all udders, 103 received selective therapy of infected half-udders, and 79 received no therapy at all. Half-udders of all animals were sampled for bacteriological study at < or = 72 h (lambing), 60 d, 120 d, and 155 d (drying-off) post partum. Dry therapy, parity number, lactation stage and therapy x parity interaction contributed significantly to variation in intramammary infection prevalence. Antibiotic dry therapy had the most significant effect. Prevalence during the whole of the subsequent lactation was significantly lower in lots receiving complete (18.8%) and selective (15.6%) dry therapy than in the untreated control lot (48.3%). Coagulase-negative staphylococci and streptococci (in particular Streptococcus agalactiae) were the organisms most significantly affected by dry therapy. In untreated ewes, prevalence increased noticeably from the 2nd to the 6th and subsequent lactations, but no significant changes were observed in the treated lots. Milk yield in the dry treated lots was 6.9% higher that in the untreated one. It was concluded that complete and selective treatments of ewes at drying-off were efficient and comparable methods of reducing the intramammary infection prevalence, improving bacteriological quality of milk, and increasing milk yield.

Detection limits of four antimicrobial residue screening tests for β-lactams in goat's milk

This study was conducted to compare the detection limits (DL) of several antibiotic residue screening tests with the maximum residue limits (MRL) authorized by the EU according to the guidance for the standardized evaluation of microbial inhibitor tests of the International Dairy Federation. Composite antibiotic-free milk samples from 30 primiparous Murciano-Granadina goats in good health condition were used to prepare test samples spiked with different concentrations of each antimicrobial. In total, 5,760 analytical determinations of 10 beta-lactam antibiotics (penicillin-G, ampicillin, amoxicillin, cloxacillin, oxacillin, dicloxacillin, cefadroxyl, cefalexin, cefoperazone, and cefuroxime) were performed using 4 antibiotic residue screening tests: the brilliant black reduction test BRT AiM (AiM-Analytik in Milch Produktions-und Vertriebs GmbH, München, Germany), Delvotest MCS (DSM Food Specialties, Delft, the Netherlands), Eclipse 100 (ZEU-Inmunotec SL, Zaragoza, Spain), and the Copan Milk Test (CMT; Copan Italia SpA, Brescia, Italy). For each method, we estimated the detection limits of the antimicrobial agents using a logistic regression model. Using the CMT and Delvotest on samples spiked with the 8 antibiotics for which MRL were available, DL were at or below the MRL. The BRT test provided DL at or below the MRL for all of the agents except cefalexin, whereas the Eclipse 100 method failed to detect 4 antibiotics (ampicillin, amoxicillin, cloxacillin, and cefoperazone) at MRL or below. Logistic regression-determined levels of agreement were highest for the CMT method (98.6 to 100%) and lowest for Eclipse 100 (66.3 to 100%). In general, agreement levels indicated good correlation between observed results and those predicted by logistic regression. The lowest b values (closely related to test sensitivity) were recorded for the cephalosporins (0.074 to 0.430) and highest for penicillin G, ampicillin, and amoxicillin (11.270 to 11.504). Delvotest and CMT best fulfilled IDF criteria for the ideal test for detecting antibiotic residues in milk.

Factors influencing variation of bulk milk antibiotic residue occurrence, somatic cell count, and total bacterial count in dairy sheep flocks.

To study the variations of bulk tank milk variables in dairy ewe flocks and to identify the main target practices and flock groups to improve milk quality and safety, a total of 71,228 records of antibiotic residue (AR) and milk yield and 68,781 records of somatic cell count (SCC) and total bacterial count (TBC) were obtained over 5 yr from the same 209 dairy ewe flocks of the Assaf breed belonging to the Consortium for Ovine Promotion of Castilla-León (Spain). Based on a logistic regression model, year, month, semester, SCC, TBC, dry therapy, and milk yield significantly contributed to AR variation. High SCC was associated with increased AR violations. When antibiotic dry therapy was implemented, AR occurrence was higher than when this practice was not used. A polynomial monthly distribution throughout the year was observed for AR occurrence; the highest values were in autumn, coinciding with low milk yields per flock. Yearly occurrences drastically diminished from 2004 (1.36%) to 2008 (0.30%), probably as a result of effective educational programs. The mixed-model ANOVA of factors influencing variation in SCC and TBC indicated that year, month, AR, dry therapy group, milking type, and year interactions were significant variation factors for SCC and TBC; mathematical model accounted for 74.1 and 35.4% of total variance for each variable, respectively. Differences in management and hygiene practice caused significant SCC and TBC variations among flocks and within flocks throughout the 5-yr study. Over time, continuously dry treated flocks showed lower logSCC (5.80) and logTBC (4.92) than untreated (6.10 and 5.18, respectively) or discontinuously dry treated (6.01 and 5.05, respectively) flocks. Continuously dry treated flocks had lower AR occurrences than did discontinuously dry treated flocks. As a whole, AR occurrence and SCC and TBC bulk tank milk variables can be used for monitoring mammary health and milk hygiene and safety in dairy sheep throughout time.

Short communication: Detection limits of non-β-lactam antibiotics in goat's milk by microbiological residues screening tests

This study compares the performance of 4 antimicrobial residue screening tests [brilliant black reduction test AiM (Analytik in Milch Produktions- und Vertriebs GmbH, München, Germany), Delvotest MCS (DSM Food Specialties, Delft, the Netherlands), Eclipse 100 test (ZEU-Inmunotec SL, Zaragoza, Spain), and Copan Milk Test (Copan Italia S.p.a., Brescia, Italy)] used to detect 20 antimicrobial agents (aminoglycosides, macrolides, tetracyclines, sulfonamides, and quinolones) in goats milk, according to International Dairy Federation guidelines. Composite milk samples from 30 antibiotic-free goats were used to prepare spiked milk samples and 11,520 analytical determinations were carried out. According to a logistic regression model, agreement coefficients were greater than 98% for most of the antibiotics, with higher b values obtained for macrolides. Neither tetracyclines nor quinolones were detected at European Union maximum residue limits. Only the Copan Milk Test and the Delvotest MCS were able to detect 3 antimicrobials below their maximum residue limits (neomycin, tylosin, and sulfadimethoxine). Given that these tests are used in control programs for goats milk, our results indicate their sensitivity would need to be improved to guarantee safety for consumers.

Daily and between-milking variations and repeatabilities in milk yield, somatic cell count, fat, and protein of dairy ewes

Abstract A total of 801 test day records were obtained consecutively over 3 days from a.m. and p.m. milkings of 267 Churra ewes belonging to two commercial dairy flocks, one machine milked and the other hand milked. The daily intervals between milkings were 14 and 10 h in both flocks during midlactation (76.2 ± 0.9 days postpartum). There were significant effects of flock, sampling day, milking time, and parity for most variables. SCC, log-transformed SCC, and fat and protein contents for the p.m. milking were higher than for the a.m. milkings. These differences are probably connected with a concentration effect owing to the lower milk yield in p.m. milking. Lowest values were always for first lactation. Daily and between-milking repeatabilities were high for yield (0.53–0.85), protein (0.61–0.78), and log SCC (0.54–0.65), but lower for fat (0.27–0.45) particularly in the machine-milked flock. Small daily variations and high repeatabilities between milkings of milk yield, log SCC, and protein makes periodic samplings possible for only one of the milkings and the use of correction factors to quantify daily total tests. Simplification of sampling procedures for fat content does not seem advisable.

Short communication: Influence of storage and preservation on microbiological quality of silo ovine milk

This study was designed to analyze the effects of the storage and preservation conditions on counts of mesophilic, thermoduric, psychotrophic, coliform, Escherichia coli, Streptococcus agalactiae, and Staphylococcus aureus organisms in silo ovine milk. A total of 910 analytical determinations were conducted from aliquots of 10 silo ovine milks. The conditions tested were unpreserved and azidiol-preserved milk stored at 4°C, and unpreserved milk stored at -20°C. Milk aged 2, 24, 48, 72, and 96 h post-collection for refrigerated aliquots, and 7, 15, and 30 d post-collection for frozen aliquots. The factors silo and storage conditions significantly contributed to variation of all microbiological variables, although milk age effect within storage was only significant for mesophilic, psychrotrophic, and coliform bacteria counts. In refrigerated raw milk, mesophile, psychrotroph, and coliform counts significantly increased over 96 h post-collection, whereas the other groups and bacteria species tested maintained their initial concentration. In all cases, azidiol preservation maintained the initial bacterial concentration in raw sheep milk under refrigeration throughout 96 h. Thus, azidiol was a suitable preservative for microbiological studies in sheep milk. Smallest counts were registered for frozen samples, particularly for coliforms, E. coli, Strep. agalactiae and Staph. aureus. Estimates of mesophilic, thermoduric and psychrotrophic organisms showed similar values on both azidiol-preserved and frozen milk samples. Coliforms and E. coli counts significantly decrease over time after freezing. Consequently, freezing at -20°C could also be appropriate for analysis of mesophilic, thermoduric, and psychrotrophic bacterial groups, but not for coliforms or mammary pathogens.

El ovino criollo chilote y su potencial productivo

Resumen Con este articulo se trata de resaltar las caracteristicas distintivas del ovino criollo Chilote (OCH) para su conocimiento y utilizacion como recurso genetico animal de gran adaptacion a las condiciones del archipielago de Chiloe, ubicado en la zona sur de Chile. Se describen las caracteristicas geomorficas del archipielago, el origen historico y cultural que rodea este recurso animal, su estructura genetica, sus caracteristicas morfologicas y productivas, asi como los sistemas de produccion en los cuales se utiliza. Palabras clave: ovinos, recursos geneticos, produccion animal Summary This article describes the characteristics of the Chilote breed of sheep (OCH) as a genetic animal resource which is highly adapted to the conditions of the Chiloe archipelago in the south of Chile. The article describes the geomorphological features of the archipelago, the historical and cultural origins of the Chilote breed, its genetic structure, its morphological and productive characteristics, and the systems of production in which it is used.

Short communication: Effect of storage and preservation on total bacterial counts determined by automated flow cytometry in bulk tank goat milk

This study was designed to evaluate the effects of different storage conditions on total bacterial count (TBC) determinations made in goat bulk tank milk using an automated flow cytometry method. The storage conditions tested were storage temperature (refrigeration at 4 and 10 degrees C or freezing at -20 degrees C), the use of a preservative (no preservative, NP; azidiol, AZ; or bronopol, BR), and the age of the milk samples for each analytical condition (storage times at 4 degrees C: from 0 h to 5 d for NP; and from 0 h to 22 d for AZ and BR; storage times at 10 degrees C: from 24 h to 2 d for NP and from 24 h to 22 for AZ and BR; storage times at -20 degrees C: from 24 h to 22 d for NP, AZ, and BR). Significant effects on individual bacterial count (IBC) variation were shown by the bulk tank milk sample, preservative, storage temperature, interaction preservative x storage temperature, and milk age within the interaction preservative x storage temperature. In preserved samples, the highest IBC were obtained for AZ and the lowest counts were obtained in samples preserved with BR. Because of the variation in IBC recorded in BR-preserved samples, we recommend that BR should not be used for TBC determinations using the automated flow cytometry method. The NP samples stored at 4 and 10 degrees C showed significantly higher IBC at 24 h postcollection, also invalidating these analytical conditions for TBC analyses. The practical implications of our findings are that goat milk samples preserved with AZ and stored at 10 or 4 degrees C are appropriate for TBC by the BactoScan flow cytometry method for up to 24 h and 11 d postcollection, respectively.

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.