PARAMETRI GENETICI DEI CARATTERI PRODUTTIVI E DELLE CELLULE SOMATICHE IN VACCHE DI RAZZA BURLINA

The Burlina is a local dual-purpose cattle breed reared in North-East Italy, particularly in Treviso province which accounts for approximately80 % of the total number of cows. The objective of this thesis was to estimate genetic parameters for daily milk yield, fat and protein contents, and somatic cell score (SCS) in Burlina breed, and explore the level of genetic variability in the population for these traits of economic relevance. Monthly test-days and pedigree datasets were provided by the Breeders Association (APA) of Treviso province. After editing procedure, 13,228 records collected on 665 cows in 10 herds from 1999 to 2009 were available. An analysis of variance (ANOVA) was carried out to identify the most important sources of variation influencing production traits and SCS. The linear model included the fixed effects of herd-test day, lactation stage, and age at calving within parity, and the random effect of error. The (co)variance components were estimated using a multivariate animal model with the same effects considered in the previous model and two new random effects: the permanent environmental and the animal. The pedigree file (988 animals) included all individuals with phenotypic records and their ancestors. (Co)variance components were then used to estimate breeding values (EBV) of animals for the traits. On average, Burlina cows produced 16.5 kg/d of milk with 3.67% of fat and 3.33% of protein, and a SCS of 3.73. Heritability estimates were 0.188 for milk yield, 0.275 for fat content, 0.358 for protein content and 0.067 for SCS. Genetic correlations between SCS and production traits were negative and low: -0.115 between SCS and milk, -0.219 between SCS and fat and -0.298 between SCS and protein. Also, very low values were estimated between milk and protein (-0.089) and milk and fat (-0.001), while a positive medium-high value was found between fat and protein (0.629). Heritability estimates along with distributions of EBVs showed the existence of genetic variability for milk yield traits and SCS in the Burlina breed. The variability could be used to improve the population, but only if additive genetic relationships among animals are considered; this is necessary to monitor and control inbreeding levels of next generations.