J.A. Carriedo

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.

Genetic parameters for lactation traits of milking ewes: protein content and composition, fat, somatic cells and individual laboratory cheese yield

The effects of some environmental variation factors and the genetic parameters for total milk traits (fat content, protein content, casein content, serum protein content, lactation mean of individual laboratory cheese yield (LILCY), lactation mean of somatic cell count (LSCC), and milk yield) were estimated from the records of 1 111 Churra ewes. Genetic parameters were estimated by multivariate REML. Heritability for fat content was low (0.10) as is usually found in the Churra breed. Heritabilities for protein content, casein content, serum protein content, LILCY, milk yield and somatic cell count were 0.31, 0.30, 0.22, 0.09, 0.26 and 0.11, respectively. The highest heritability estimates were for protein and casein contents. Casein content is not advisable as an alternative to protein content as a selection criterion for cheese yield improvement; it does not have any compelling advantages and its measurement is costly. Our results for LSCC indicated that efforts should focus on improving the level of management rather than selecting for somatic cells, in the actual conditions of the Churra breed.

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.

Genetic correlations and heritabilities for milk yield and lactation length of dairy sheep

Abstract A total of 6917 lactation records for 1569 Churra dairy sheep raised in a single flock, over the years 1977–96, were used to estimate genetic parameters for total milk yield (TMY), standardized milk yield (SMY) and lactation length (LL). Estimates for heritability and genetic correlations among TMY, SMY and LL studied in this work were obtained employing multitrait analysis with a repeatability animal model. The model accounted for year–season effect, parity and type of birth as single or multiple lambings. Heritabilities for TMY, SMY and LL were 0.27±0.036, 0.25±0.034 and 0.015±0.010, respectively. The corresponding figures for repeatabilities were 0.41±0.013, 0.38±0.013 and 0.040±0.010, respectively. Genetic correlation between TMY and SMY was 0.99, whereas genetic correlations of LL with TMY and SMY were 0.61 and 0.62, respectively. Phenotypic correlations were 0.97, 0.10 and 0.25, respectively. Residual correlation between TMY and LL was 0.21 and only 0.01 between SMY and LL. Product moment and rank correlations between genetic evaluation of sires based on TMY with that based on SMY records were 0.85 and 0.84, respectively. As expected, these correlations were lower than the true genetic correlation between TMY and SMY mainly due to the accuracy of breeding value predictions for both traits. Results indicate heritabilities in the range found in the literature for TMY and SMY. The low heritability estimate found for LL confirmed that this trait is mainly affected by environmental conditions. Because of the low heritability estimate found for LL, the lower residual correlation between SMY and LL, both close to zero, and the equal genetic correlation of LL with both TMY and SMY, it seems better to use SMY than TMY for selection programs of Churra dairy sheep.

An individual laboratory cheese-making method for selection in dairy ewes

Abstract A new analytical method to quantify individual laboratory cheese yield (ILCY) of ewe’s milk, on the basis of milk quantities compatible with those of the official milk recording (OMR), was elaborated. The method was firstly evaluated within laboratory and secondly applied to a large number of milk samples belonging to various flocks of the Churra breed in order to study the ILCY behavior under real field conditions. The method demonstrated an acceptable performance within the laboratory and under field conditions. ILCY was close to real cheese yield in dairy ewes. It showed a normal distribution and an evolution during the lactation period consistent with the fat and protein contents of the milk. This is of considerable significance for dairy ewe recording schemes where analysis of a large number of samples is required.

Genetic and environmental estimations for test-day and standardized milk yield of dairy sheep

Three sets of data, standardized 120-day milk yield, corresponding test-day yields and the first two test-day yields of Churra ewes were considered to estimate genetic and environmental parameters of milk yield. A total of 22 599 lactation milk yields and their corresponding 84 488 test-day yields for 12 785 ewes, collected between 1992 and 1994, were used to estimate environmental parameters employing fixed models. A subset including data from the daughters of the rams participating in the breeding program was used for the estimation of genetic parameters (3379 lactations and their corresponding 12 662 test-day yields for 2102 ewes, the daughters of 121 rams). Heritabilities and repeatablities were estimated by derivative free restricted maximum likelihood and breeding values of the rams were estimated by a repeatability animal model. For test-day milk yield, the environmental effects of the fixed model, including flock test-date (FTD), age at lambing, type of birth, and linear, quadratic, and cubic coefficients of days in milk and their inverses, were all highly significant (P<0.001). For 120-day milk yield, flock–year–season, age at lambing, and type of birth all had highly significant effects (P<0.001). However, interval from lambing to first test had a less significant effect (P<0.05). The heritabilities estimated for all test-day yields, the first two test-day yields and 120-day milk yields were 0.14, 0.15 and 0.18, respectively. These heritabilities were all low, mainly because of the higher phenotypic and residual variances obtained. The corresponding repeatability estimates for the same traits were 0.44, 0.46 and 0.42, respectively. Product moment and rank correlations between breeding values of rams based on 120-day milk yield and those based on all test-day milk yields and the first two test-day yields ranged from 0.77 to 0.88. Product moment and rank correlations between evaluations based on all test-day yields and on the first two test-day yields were 0.94 and 0.92, respectively. FTD models presented a possible alternative to models fitting standardized yield records.

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.

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.

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.

Association between ovine protein polymorphisms and geographical variables in Europe and south-west Asia.

SUMMARY The spatial distribution of six blood-protein polymorphisms in European and south-west Asian ovine breeds was analysed. Latitudinal clines were found for haemoglobin and transferrin loci. The respective F(ST) values are not significantly greater than those for protein-X, esterase, carbonic anhydrase, and albumin, where gene frequencies are not associated with latitude. The results suggest that historical processes of gene flow, rather than adaptation to different environments, have played a major role in determining the observed lives of gene frequencies. RESUMEN: Asociación entre polimorfismos proteicos ovinos y variables geográficas en Europa y sudoeste de Asia Se ha analizado la distribución espacial de seis polimorfismos proteicos sanguíneos en razas ovinas de Europa y del sudoeste de Asia. La hemoglobina y la transferrina muestran clinas latitudinales. Los valores de F(ST) para estos dos loci no son significativamente más grandes que los de la proteína-X, esterasa, anhidrasa carbónica y albúmina, cuyas frecuencias génicas no están asociadas con la latitud. Los resultados sugieren que la distribución de las frecuencias génicas de la hemoglobina y la transferrina se debe a procesos históricos de flujo génico y deriva genética.