Genotype-by-Environment Interactions and Response to Selection for Milk Production Traits in Lacaune Sheep from Greece and France

The objective of the study was two-fold and is as follows: (i) to investigate genotype-by-environment (G × E) interactions for milk yield and composition in purebred Lacaune sheep reared intensively in Greece and semi-extensively in France, and (ii) to estimate the potential genetic gain of selection based on genetic evaluations jointly calculated in both countries compared to each country separately. A total of 1658 Lacaune ewes from 4 intensive farms in Northern Greece and 4859 Lacaune ewes from 186 semi-extensive farms in Southern France were used. Ewes in the two countries were daughters or granddaughters of the same rams (6 common sires and 11 common grandsires). Individual ewe milk yield was recorded monthly, and milk samples were collected to assess their chemical composition. The total milk yield and milk component content were calculated. Results showed a strong genetic correlation for milk yield (0.86 ± 0.13, <i>p</i> < 0.05) and protein content (0.88 ± 0.12, <i>p</i> < 0.05) between the two countries, suggesting no strong evidence of G × E interaction. In the case of fat content, a moderate correlation was found (0.59 ± 0.21, <i>p</i> < 0.05) indicating some degree of sire re-ranking. Results suggest that a joint genetic evaluation and selection of Lacaune sheep in Greece and France is feasible. Simulations showed that selection across countries is estimated to increase genetic gain up to 68.17% and 0.16% in Greece and France, respectively, as compared to selection within a country.