Genetic Parameters for Functional Longevity, Type Traits, Somatic Cell Scores, Milk Flow and Production in the Italian Brown Swiss

Abstract

The aim of this study was to estimate genetic parameters for a set of new traits and to update values for production and morphological traits to be used in the selection index of Italian Brown Swiss dairy cattle. Longevity, milking speed and somatic cell scores (SCS) were considered for inclusion in the selection index, and (co)variances with all traits of the selection index were estimated. SCS was considered on a lactation basis while milk flow, the amount of milk (kg) released per time unit (minute), was measured with a flowmeter. Cow functional longevity was the total herd life corrected for the production level. A total of 127,416 first lactation records of cows calving from 1985 to 2003 were considered. In order to maximize the number of records available for each combination of traits, 9 data sets were created. Estimates were obtained from multivariate linear sire models with equal design matrix in subsequent separated analysis. REML algorithms and canonical transformation were used to calculate (co)variance estimates among all traits: functional longevity, milking speed, SCS, 5 production traits (milk, fat and protein yield, fat and protein percent), and 19 type traits. Heritabilities estimated were 0.14±0.02 for SCS, 0.33±0.07 for milk flow, and 0.04±0.01 for functional longevity. Genetic correlation values between SCS and milk yield, fat percent and protein percent were 0.18±0.09, −0.19±0.08, and −0.22±0.08, respectively. Functional longevity had a strong positive genetic correlation with udder depth (0.42±0.10) but a negative correlation with rear leg set (−0.56±0.10). Milk flow was positively correlated with most of the production measures: 0.30±0.18 with milk yield, 0.24±0.17 with fat yields, 0.16±0.20 with protein yield. Additionally, milk flow was genetically correlated with some type traits (0.53±0.14 rear udder width, 0.40±0.16 hock quality, 0.32±0.15 rump angle, −0.25±0.19 udder depth). The correlation between SCS and milk flow showed a value of 0.46±0.26, indicating that faster cows are more susceptible to mastitis.