Latxa Dairy Sheep Research Articles

Environmental and additive genetic factors that affect artificial insemination success in Latxa dairy sheep breed

In the Latxa breed, flocks within the breeding program make use of high genetic value rams to inseminate their ewes once per year. Despite the relevance of the insemination results in the genetic progress and on farms’ productivity, external and genetic factors that affect artificial insemination (AI) success have not been up to now explored in this sheep population. For that, 135,351 edited AI records from 63,480 inseminated Latxa Cara Negra from Euskadi ewes, using 853 service rams, collected between 2000 and 2021, were used. The outcome of an AI event was treated as a binary response of either success or failure in becoming pregnant. To identify the environmental factors influencing the AI result, a multiple logistic regression was first calculated on a selection of variables related to the ewes, to the ram, and to other non-sex-specific aspects. With relevant variables detected, a threshold model, including the pedigree information of the inseminated ewes and the service rams, was used to estimate the genetic components of the trait in both sexes. Findings show that the AI success is higher in ewes who had the previous parturition from an AI event, in those with a lambing-AI interval longer than 210d, with 3 years and 2 lambings, with high prolificacy and in those having their first parturition at 1 year of age rather than at 2 or 3 years of age. In counterpart, the higher the milk produced in the nearest record before AI date, the poorer the AI results. Furthermore, relevant variability was linked to the year of insemination, the herd and the technician in charge of the insemination procedure. Regarding genetic parameters, heritability values, on the observable scale, and repeatability were 0.057 ± 0.004 and 0.204±0.007 in females and 0.009 ± 0.037 and 0.032 ± 0.002 in males, respectively. These results evidence that the AI success is under moderately low additive genetic control, with the surrounding environmental variables being the strongest controlling factor. An effort to enhance some farm management practices should be encouraged to efficiently improve reproductive results. Although genetic selection on AI success is viable, the genetic progress may be scarce. An option to improve reproduction by means of selective breeding might be the development of a multi-trait index.

Impact of truncating historical data on prediction ability of dairy sheep selection candidates

Along the last decades, the genetic evaluation methodology has evolved, improving breeding value estimates. Many breeding programmes have historical phenotypic records and large number of generations, but to make use of them could result in more inconveniences than benefits. In this study, the prediction ability of genotyped young animals was assessed by simultaneously evaluating the removal of historical data, two pedigree deepness and two methodologies (traditional BLUP and single−step genomic BLUP or ssGBLUP), using milk yield records of 40 years of three Latxa dairy sheep populations. The linear regression method was used to compare predictions of young rams before and after progeny testing, with six cut-off points, by intervals of 4 years (from 1992 to 2012), and statistics of ratio of accuracies, bias, and dispersion were calculated. The prediction accuracy of selection candidates, when genomic information was included, was the highest in all Latxa populations (between 0.54 and 0.69 with full data set). Nevertheless, the deletion of historical phenotypic data resulted on moderate accuracy gain in the bigger data size populations (mean gain 2.5%), and the smaller population took advantage of a moderate data deletion (2.7% gain by removing data until 2004), reducing accuracy when more records were removed. The bias of validation individuals was lower when the breeding value was predicted based on genomic information (between 2.1 and 13.9), being lower when the biggest amount of data was deleted in the bigger data size populations (5.2% reduction), and the smaller population was benefited from data deletion between 1996 and 2008 (3.8% bias reduction). Meanwhile, the slope of estimated genetic trend was lower when less data were included, and an overestimation of the unknown parent group estimates was observed. The results indicated that ssGBLUP evaluations were outstanding, compared with traditional BLUP evaluations, while the depth of pedigree had a very small influence, and deletion of historical phenotypic data was beneficial. Thus, Latxa routine genetic evaluations would benefit from truncating phenotypic records between 2000 and 2004, the use of two pedigree generations and the implementation of ssGBLUP methodology.

An approach to functional longevity in Latxa dairy sheep

Productivity and profitability of sheep farming are strongly influenced by the productive performance of ewe during it lifetime. For that, it is relevant to quantify the genetic and non-genetic factors affecting functional longevity in order to consider its inclusion as a trait in a breeding scheme. In this investigation, a Weibull proportional hazard model was applied to study the length of productive live as functional longevity indicator in Latxa dairy sheep breeds. The time from the first calving to the date of culling was individually calculated using records from 28,466 Latxa Cara Rubia (LCR), 26,045 Latxa Cara Negra from Euskadi (LCNEAE) and 10,385 Latxa Cara Negra from Navarre (LCNNAF) from commercial flocks, born between 2000 and 2018. The culling risk associated to the age at first lambing, number of lambs born per lambing and total milk yield produced per lactation was estimated using a likelihood ratio test, and the genetic component of longevity was estimated using a sire-maternal grandsire model. The results concerning the relative culling risk showed that ewes having their first lambing at 2 years of age had around 1.30 times more risk of disposal compared with those of 1 year, regardless of the Latxa population. Similarly, it was found that LCR and LCNEAE having 2 o 3 lambs born per lambing had 1.20 and 1.34 higher risk to be culled in comparison to having 1 lamb, whereas the risk was 1.04 in LCNNAF. In contrast, the probability to be culled was drastically reduced by around 1.50 in all the Latxa populations as the milk yield moved from low to intermediate levels and by around 3.0 times when it moved from low to high. Regarding the genetic parameters of longevity, heritability values ranged from 0.042 to 0.061, which indicates that it is under low additive genetic control. Furthermore, a decreasing genetic was observed, although the decrease rate was smaller during recent years possibly due to the parallel improvement on udder traits. In the light of the results of this first longevity study in Latxa, it is possible to infer that ewes’ on-herd durability is negatively affected by a reproductive delay and a high prolificacy, whereas the higher the milk production, the lower the risk. Moreover, given the genetic findings, it can also be deduced that although selection on longevity is viable, the genetic progress may be a long process.

High genetic correlation for milk yield across Manech and Latxa dairy sheep from France and Spain

Spanish Latxa and French Manech are dairy sheep breeds that split into Blond (Latxa Cara Rubia, LCR; Manech Tête Rousse, MTR) and Black (Latxa Cara Negra of Navarre, LCN; Manech Tête Noire, MTN) strains. Exchange of genetic material (artificial insemination doses) is becoming more and more frequent across these breeds, within color, to boost both genomic precision using a larger reference population and genetic progress using a larger selection base. This exchange leads to some rams having descendance across both countries. However, additional gains can only be achieved if the selected traits are genetically similar across countries. The objective of this work was to estimate the genetic correlation across breeds for milk yield. We combine across-country, within-color records, pedigree, and marker information. The number of animals with records oscillates from 65,000 (LCN) to 544,000 (MTR), whereas the number of connecting artificial insemination rams (with more than 10 daughters in the other country) is 381 MTR rams in LCR and 58 MTN rams in LCN. Blond strains had a stronger and more extended-in-time connection. The number of genotyped rams goes from 328 (LCN) to 4,901 (MTR). The relatedness of populations was assessed by principal component analysis and Fst coefficients. The genetic correlation was estimated using 2 (one per color) 2-trait models (each country a trait), including all available data (records, pedigree and genotypes), by maximum profile likelihood while fixing other variance components to within-population estimates. Results showed a closer genetic relationship of Blond strains than of Black strains (Fst: 0.01 vs. 0.05, respectively). Genetic correlation estimates for milk yield were 0.70 in both cases. Based on Fst distances, we expected a lower correlation for Black strains than for Blond ones if dominance or epistasis are important. Thus, we attribute the value of this correlation not being close to 1 mostly to genotype-by-environment interaction, including on-farm management and trait modeling. Regardless, the correlation of 0.7 across populations is encouraging for future joint work of Latxa and Manech breeders, including joint genetic evaluations.

Exploring the inclusion of genomic information and metafounders in Latxa dairy sheep genetic evaluations

The availability of genomic marker panels has made possible more precise estimates of breeding values. Sheep breeding programs are implementing genomic selection. In Latxa dairy sheep breed, a previous study using pre-corrected data and a small number of genotyped animals did not show a clear advantage of genomic selection. The objective of the present study was to ascertain the possible benefits of GS for the Latxa breed based on more data than before and using better tools, in particular single-step genomic BLUP using metafounders to model missing pedigree. Goodness of prediction of pedigree and genomic evaluations was analyzed by cross-validation comparing predictions of young rams using whole and partial (truncated) data sets. The results showed that with the current available data, genetic and genomic evaluations have the same accuracy. Contrary to the previous study, predictions were nearly unbiased, which shows the advantage of using single-step genomic BLUP. However, genomic information did not yield more precise evaluations. This could be explained by the small number of sibs in the young rams.

Exploring the inclusion of genomic information and metafounders in Latxa dairy sheep genetic evaluations

Exploring the inclusion of genomic information and metafounders in Latxa dairy sheep genetic evaluations

Inbreeding, effective population size, and coancestry in the Latxa dairy sheep breed

Traditionally, breeding programs have estimated and managed inbreeding based on pedigree information. The availability of genomic marker panels has made possible new alternatives to achieve more precise estimates, for example in case of missing pedigree. The objective of the present study was to assess and compare, different estimation methods (pedigree-based methodologies, single SNP-based approach (homozygosity) and runs of homozygosity-based method) to analyze the evolution of genetic diversity measured as inbreeding or as coancestry of 3 selected populations of Latxa dairy sheep (Latxa Cara Rubia and Latxa Cara Negra from Euskadi and Navarre). Genomic data came from 972 artificial insemination rams genotyped with the Illumina OvineSNP50 BeadChip (Illumina Inc., San Diego, CA) whose genealogy consisted of 4,484 animals. Inbreeding estimates based on molecular data were more similar between them than compared with those based on pedigree information. However, the SNP-based approach estimations of effective population size differed more, reflecting the sensitivity of effective population size to small changes in the evolution of inbreeding. The 2 Latxa Cara Negra populations showed increases of inbreeding rates with time and effective population sizes between 64 and 103 animals, depending on breed and methodology used. The Latxa Cara Rubia population did not show an increase in inbreeding rate, mainly due to semen importation from the related French population of Manech Tête Rousse. The effective size estimates based on coancestry increase show a higher variability and they are more sensitive to the source of information and the data structure considered. Realized effective population size based on individual increase in inbreeding were in agreement with the previous estimates. Coancestry evolution analysis based on DNA information showed an increase on coancestry during the last 10 yr in all breeds, as a consequence of the selection process. Moreover, the increase on coancestry between Latxa Cara Rubia and Manech Tête Rousse was more noticeable between than within each of those breeds.

Milk production losses in Latxa dairy sheep associated with small ruminant lentivirus infection

Visna/Maedi is a disease of sheep caused by small ruminant lentivirus (SRLV) infection that is widespread throughout the world and that has been recognized to be present in the Basque Country (Spain) since the early 1980′s. Nearly seven decades of studies have improved the knowledge on its clinical signs and epidemiology. However, its slow progressive nature, subclinical most of the time, makes difficult to assess its real impact on productive traits, a question of critical importance to balance out the economic costs it causes and the benefits of designing and deploying an eradication program. Development of a dairy breeding program since the 90 s in the local Latxa sheep population has provided data on milk productivity in several flocks where SRLV infection prevalence has been continuously monitored. This study analyses retrospectively the association between SRLV prevalence and production variables during ten yearly lactations in three Latxa dairy flocks with medium-high SRLV seroprevalence. Our results indicate that average standard lactation of seropositive sheep was 6.7 % lower than controls. The largest differences (p < 0.001) were observed at the ewe lifetime peak of production between second and fourth lactations. Lifelong milk and lamb production data indicated even a higher impact, with costs rising up to nearly 50 €/ewe/year. This substantial production decrease associated with subclinical SRLV infection in Latxa dairy sheep supports the benefit of establishing a SRLV control program. A rough cost-benefit analysis indicated that even in a medium-yielding breed, testing expenses would be largely covered by milk production improvement.

SNPs in candidate genes MX dynamin-like GTPase and chemokine (C-C motif) receptor-5 are associated with ovine pulmonary adenocarcinoma progression in Latxa sheep.

Ovine pulmonary adenocarcinoma (OPA) is a contagious lung cancer in sheep caused by Jaagsiekte sheep retrovirus (JSRV). OPA is present in many sheep-rearing countries causing economic and welfare issues, as currently no efficient vaccines or treatments are available. Breed differences suggest a host genetic component may influence the pathogenesis of OPA, but so far few genes have been identified. In this work, a genetic association study was carried out in Latxa dairy sheep which were classified as cases/controls based on the presence/absence of OPA lung tumours. Candidate genes included cytokines and a receptor and innate immunity genes. After SNPs in the candidate genes were identified, the distribution of alleles in cases and controls was compared by means of logistic regression analyses at the allelic, genotypic and haplotypic levels. The association analysis showed that several candidate genes were significantly associated with resistance or susceptibility to OPA; two of the candidates, CCR5 and MX1, remained significantly associated with resistance and susceptibility respectively, even after Bonferroni correction.

Rapeseed and sunflower oilcake as supplements for dairy sheep: animal performance and milk fatty acid concentrations.

The influence of different amounts of oilseed cake (rapeseed and sunflower) on animal production parameters and fatty acid (FA) concentrations of the milk was studied in a Latxa dairy sheep experimental flock, both in winter (50% oilcakes; indoor feeding) and in spring (30% oilcakes; part-time grazing). The two different levels of the oilcakes tested did not affect animal production parameters or milk yield. Milk fat content and the fat/protein ratio decreased significantly with 30 and 50% sunflower cake. Yet, fat/protein ratio values were within the range for cheesemaking. Both levels of either type of oilcake tested significantly increased the concentrations of nutritionally interesting FA (CLA isomer C18:2cis-9, trans-11, vaccenic, oleic, and total unsaturated FA), while simultaneously decreasing the concentration of atherogenic FA. The atherogenicity indexes of milks from ewes fed 50 or 30% of either oilcake were significantly lower than those of their corresponding control. The use of cakes in winter increased the concentration of nutritionally interesting FA to the values obtained with part-time grazing.

Short communication: Analysis of association between the prion protein (PRNP) locus and milk traits in Latxa dairy sheep

The purpose of this study was to analyze associations between polymorphisms in the PRNP gene and ewe milk traits. A total of 242,565 lactations of the Latxa breed were used. Milk, fat and protein yields, and fat and protein content from black-faced Latxa from Spanish Basque Country, black-faced Latxa from Navarra, and blond-faced Latxa were collected. To evaluate evidence of association, the different traits were analyzed using an animal model, where the PRNP genotype effect was included or not as a random effect. Adding the PRNP effect to the model improved the fitting for milk yield in black-faced Latxa from Spanish Basque Country and in blond-faced Latxa, for fat yield in black-faced Latxa from Navarra, and for protein yield in blond-faced Latxa. However, the proportion of the phenotypic variance explained by the PRNP effect for milk yield (1.0×10−3), fat yield (3.6×10−3) and protein yield (9.4×10−4) were near zero. The PRNP locus accounts for about 0.5, 1.5, and 0.4% of total genetic (PRNP and polygenic) variance in milk, fat, and protein yield. These values indicated that the PRNP effect is not relevant regarding genetic additive contribution. For breeding purposes, it is unlikely that selection for scrapie resistance will have an effect on the milk traits studied in the Latxa breed.

Lamb mortality in an outbreak of Yersinia pseudotuberculosis mastitis, as a collateral effect of colostrum feeding for Lentivirus-control

Yersinia pseudotuberculosis infections have been reported in a wide range of wild and domestic hosts, as well as humans. There have been some reports on involvement of this pathogen in the aetiology of mastitis in cows and goats, but apparently not in sheep. We report here a case where subclinical mastitis in a Latxa dairy sheep flock appeared to cause an outbreak of perinatal mortality, as a consequence of unknowingly feeding infected colostrum for preventing vertical transmission of Small Ruminant Lentivirus. The flock was composed of 188 ewes that had lambed in late-January 2008. Deaths of 3–5-day-old lambs reached 50% mortality of lambs born on the 20th and the 21st day of the outbreak and then decreased, averaging 34% out of 105 lambs born during a 6-day period. Affected lambs appeared inactive and ceased eating and growing. Two lambs submitted for post mortem examination showed necrosuppurative enterocolitis, mesenteric lymphadenitis, necrotizing hepatitis, splenitis and pneumonia. Bacterial culture yielded Y. pseudotuberculosis. It was noticed that all sick lambs had been fed with colostrum from a single ewe that had three lambs on the 20th January. All that colostrum had been consumed, but the milk of all animals in the flock was immediately submitted to the California Mastitis Test (CMT). Several ewes resulted positive, but only two yielded any significant isolation, which was in both cases of Y. pseudotuberculosis. One was also a colostrum donor. Treatment with enrofloxacin was immediately given to the surviving lambs and these showed a quick recovery. All the contaminated bulk milk was destroyed after the first Y. pseudotuberculosis isolation from milk samples; the two infected ewes were separated and dried-off on a treatment with enrofloxacin immediately and at the end of lactation, respectively. On the 71st day, the donor ewe was killed after showing an acute mastitis, from which Y. pseudotuberculosis was recovered. The surviving ewe, that carried two foetuses, suffered pregnancy toxaemia 1 week after being transferred to new facilities nine months later. Stenotrophomonas maltophilia was isolated from placenta, right mammary gland and faeces and Escherichia coli from the intestine and lung, but no Y. pseudotuberculosis was recovered from any sample. Regarding use of colostrum, it was concluded that it is necessary to always check it with the CMT before using it for lambs on artificial lactation.

Bayesian model selection of contemporary groups for BLUP genetic evaluation in Latxa dairy sheep

Milk yield data from the Latxa dairy sheep breed were used for model comparison. Three possible models for genetic evaluation, differing in the definition of the contemporary groups, were compared using a Bayesian approach. Contemporary groups were: flock–year+flock–month of lambing–number of parity and age, flock–year–month, and flock–year in models 1, 2, and 3, respectively. All available data from the two strains of the breed (Black-Faced and Blond-Faced) were used. The comparison criteria were: Bayes factor, posterior Bayes factor, pseudo-Bayes factor, two checking functions based on univariate predictive distributions, and the deviance information criteria. The two checking functions consisted in the measure of accuracy ( d 1) and systematic bias ( d 2) in the prediction of observations. All criteria except d 2 indicated the superiority of model 2 in both strains. Based on these results, it was concluded that model 2 reaches the best equilibrium between fit and predictive ability.

Genetic parameters of milk traits in Latxa dairy sheep

AbstractA total of 7444 lactation records which include milk, fat and protein yields (MY, FY, PY) and fat and protein content (F%, P%) from 6429 Black-Faced Latxa ewes were employed to estimate genetic parameters for milk traits. Traits were standardized to 120 days of lactation. For the calculation of composition traits, not all test-days had their composition measured and therefore a correction taking this into account was included in the analysis. A first-derivative restricted maximum likelihood algorithm was used on an animal model with repeatability analysis, using models including fixed effects (flock-year-season of lambing, age-parity at lambing, number of lambs, interval between lambing and first milk recording and the combination of sampled test-days) and random effects (the additive genetic effect and the permanent environmental effect). The resulting heritabilities were 0·20, 0·16, 0·18, 0·14 and 0·38 for MY, FY, PY, F% and P% respectively. Heritability of F% was much lower than expected, probably due to problems derived from the recording method. Genetic correlations were high and positive between yields and moderately positive between F% and P%, and negative or null between yields and composition, as has been reported for other European dairy sheep breeds. As most of the milk produced by Latxa dairy sheep is processed into cheese, the inclusion of milk sampling in official milk recording and a change in the selection criterion are recommended to avoid a long-term worsening in milk composition.

The effect of the lambing distribution on the evolution of bulk tank milk composition in the Latxa dairy sheep of the Basque Country (Spain)

According to the lambing distribution more than 90% of the Latxa flocks existing in the Spanish Basque Country can be classified into four typologies (Oregui et al., 1996, Ruiz et al., 1997). Generally speaking, flocks located in the highlands or mountainous areas (Groups 1 and 2) usually concentrate the lambing season at the end of winter. As winter conditions are less severe, lambings tend to begin before (early-winter or late-autumn) and follow a more scattered pattern (Groups 3 and 4). The objective of this analysis was to study the possible relationship between lambing distribution and solids composition of bulk tank milk, which affects cheese-making performances at the farm.

Comparison of Models for Describing the Lactation Curve of Latxa Sheep and an Analysis of Factors Affecting Milk Yield

The objectives of this work were 1) to compare the goodness-of-fit of empirical models of the lactation curve and 2) to analyze the factors affecting the shapes of the lactation curves, the parameters describing them, and the overall milk yield of Latxa dairy sheep. A total of 14,699 records from 2711 ewes, collected during three consecutive years (1995 to 1997) by the milk recording program of the Latxa ewe of the Basque Country (Spain), were used. Six mathematical models and three fitting procedures were compared. The estimation of model parameters by nonlinear fitting procedures was superior to that by linear regression methods. A nonlinear variable decay model fitted the data better than the other models, as judged by lower mean square prediction error, residual sums of squares, and a lack of first-order positive autocorrelation as assessed by the Durbin Watson coefficient. The effects of the flock, flock-year interaction, month of lambing, length of lactation nested within month of lambing, parity, and number of live lambs born had significant effects on the parameters of the model and the total milk yield (P<0.01). The prediction of milk yield from the selected model was similar to the estimates obtained with the Fleischmann method currently used by the national breeding program for the Latxa breed.

Genetic Parameters and Trends for Milk Production of Blond-Faced Latxa Sheep Using Bayesian Analysis

The genetic progress attained with the breeding scheme of the blond-faced Latxa dairy sheep in the Spanish Basque Country was assessed by a Bayesian approach based on the marginal posterior distributions of parameters achieved via Gibbs sampling. The data file included 49,056 milk yield records of 22,363 ewes. Normal distributions were assumed for EBV and fixed effects, and scaled inverted chi-square distributions were assumed for variance components or additive, permanent environment, and residual effects. Under vague priors for variance components, the posterior means (SD) for heritability and permanent environment coefficient for milk yield at 120 d were 0.22 (0.01) and 0.20 (0.01). An important effect on the milk yield (41.6% of the mean) was evident for a genetic group of imported rams. Selection was effective for sheep that were bred by AI and that had known parents. The robustness of results for effect of genetic group and genetic trends was validated using a mildly informative prior constructed from variance components estimated with the related black-faced Latxa breed.