Within- and across-breed genomic predictions and genomic relationships for Western Pyrenees dairy sheep breeds Latxa, Manech, and Basco-Béarnaise.

Genotypes, phenotypes and pedigrees of 6 breeds of dairy sheep (including subdivisions of Latxa, Manech, and Basco-Béarnaise) from the Spain and France Western Pyrenees were used to estimate genetic relationships across breeds (together with genotypes from the Lacaune dairy sheep) and to verify by forward cross-validation single-breed or multiple-breed genetic evaluations. The number of rams genotyped fluctuated between 100 and 1,300 but generally represented the 10 last cohorts of progeny-tested rams within each breed. Genetic relationships were assessed by principal components analysis of the genomic relationship matrices and also by the conservation of linkage disequilibrium patterns at given physical distances in the genome. Genomic and pedigree-based evaluations used daughter yield performances of all rams, although some of them were not genotyped. A pseudo-single step method was used in this case for genomic predictions. Results showed a clear structure in blond and black breeds for Manech and Latxa, reflecting historical exchanges, and isolation of Basco-Béarnaise and Lacaune. Relatedness between any 2 breeds was, however, lower than expected. Single-breed genomic predictions had accuracies comparable with other breeds of dairy sheep or small breeds of dairy cattle. They were more accurate than pedigree predictions for 5 out of 6 breeds, with absolute increases in accuracy ranging from 0.05 to 0.30 points. They were significantly better, as assessed by bootstrapping of candidates, for 2 of the breeds. Predictions using multiple populations only marginally increased the accuracy for a couple of breeds. Pooling populations does not increase the accuracy of genomic evaluations in dairy sheep; however, single-breed genomic predictions are more accurate, even for small breeds, and make the consideration of genomic schemes in dairy sheep interesting.

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.

High repeatability of the amplitude and duration of the nycthemeral rhythm of the plasma melatonin concentration in the Ile-de-France ewe.

In order to determine individual variability in the amplitude and duration of the nycthemeral rhythm of the plasma melatonin concentration, 12 ovariectomized estradiol-treated Ile-de-France ewes were submitted to a sequence of 34 long days (LD1, 16L:8D), 21 short days (SD, 8L:16D), and 21 LD (LD2). Intensive blood sampling (hourly from 1 hr before dusk to 1 hr after dawn) was performed for 4 consecutive nights in each of the photoperiodic situations (LD1, SD, LD2), i.e., a total of 12 nights per ewe. Plasma melatonin was assayed by radioimmunoassay. Instantaneous amplitude (difference between each hourly measurement of the plasma melatonin concentration during the nocturnal elevation and the mean diurnal melatonin concentration), mean individual amplitude (same definition but using the mean melatonin concentration during the nocturnal elevation) and duration of elevation of plasma melatonin concentrations were calculated for each ewe and each night and analyzed by variance analysis. Instantaneous amplitude varied significantly with photoperiod, with night intra-photoperiod, with ewes, and time intra-night. Mean individual amplitude varied significantly with photoperiod and with ewe but not with night intra-photoperiod. Dramatic differences between individuals appeared in the amplitude and duration of melatonin rhythms. The lowest mean individual amplitude (all nights of measurement) found was 95 pg/ml and the highest was 544 pg/ml. Overall repeatability coefficient of the mean amplitude of melatonin elevation was 0.71 (P < 0.001). Duration of melatonin elevation varied significantly with photoperiod, with nights intra-photoperiod and with ewes. During LD periods, mean duration of melatonin elevation was equivalent to duration of the night (from 7 to 8 hr), while during SD it varied with ewes from 9 to 16 hr. Repeatability coefficient of the duration of melatonin elevation in SD was 0.57 (P < 0.05). It is concluded that amplitude and duration (in SD) of the nycthemeral rhythm of the plasma melatonin concentration are highly repeatable individual characteristics in the ewe.