Applicazione di uno strumento genomico per la selezione della rimonta femminile

The choice of farm rebreeding is a key operation to consolidate farm income in future years and must be as careful as possible to obtain a herd suited to production needs.With genomic selection, much emphasis has been placed on productive traits that have high heritability and allow the breeder to increase income in a short time.In recent years, the focus has been on longer-lived animals that can stay on the farm for longer by ensuring an optimal number of lactations.Therefore, more weight has been given to traits with low heritability, such as the functional traits, including disease resistance.Mastitis is one of the major diseases that despite selection for SCS (somatic cell score) and monthly functional checks is the cause of large farm losses, both due to early culling of animals and milk losses.The replacement selection that includes resistance for mastitis would result in more functional cows with more consistent milk yields, and lower costs of veterinary fees and drug use.This study aims to investigate the applicability of a genomic tool developed internationally for the choice of farm replacement in the reality of the Piedmont region. Ten farms were selected based on their average SCC in the period between 2014-2019.This resulted in 2 groups classified as: Low SCC (LS), with SCC below 150,000 cells/mL, and High SCC (HS), with SCC above 300,00 cells/m. The farms used only genomic sires on the basis of PFT index for genetic improvement, and the choice of replacement was on a phenotypic basis.For each farm, biological samples were taken from 15% of the available heifers and sent to the United States for genomic testing.A total of 3 production indices (milk production, protein and fat) and 2 indices for mastitis resistance (SCS and Z_MAST) were analysed.The animals were followed throughout the first lactation by collecting data from monthly functional checks.Analysing the data of the functional controls of the farms, the results lead to consider that the two groups represent two different management and health levels, as the LS farms obtained on average a lower SCC value, higher milk production (Kg) and fat production (%) than the HS.The genomic indices were found to be not different in milk production and Z_MAST index, which was predictable as both realities selected using only the National PFT index.This composite index also includes the SCS index, for which LS heifers are found to possess on average better indices than HS heifers.The results support the hypothesis that the LS farm reality favours a more effective selection by the breeder of animals with superior genetics even through mere observation of the phenotype of the dams.The Pearson correlation existing between the SCS and Z_MAST indexes confirm their correlation with mastitis resistance.Then analysing the productions of cows, the results confirm that LS farms are able to achieve a better expression of the genetic potential of their animals.Correlation analyses between phenotypes and related indexes confirm on average a higher correlation for LS farms than HS farms.Supporting the initial hypothesis that animals on LS farms exhibit a phenotype more consistent with the genotype, making the choice for rebreeding more accurate even using only the phenotype of the dams.In conclusion, the study showed that the genomic predictions were correct and also confirmed the high potential of a genetic selection approach based on genomic analysis of females in the Italian territory.