Abstract
The aim of this study was to estimate genetic associations between alternative somatic cell count (SCC) traits and milk yield, composition and udder type traits in Italian Jersey cows. Alternative SCC traits were test-day (TD) somatic cell score (SCS) averaged over early lactation (SCS_150), standard deviation of SCS of the entire lactation (SCS_SD), a binary trait indicating absence or presence of at least one TD SCC >400,000cells/ml in the lactation (Infection) and the ratio of the number of TD SCC >400,000 cells/ml to total number of TD in the lactation (Severity). Heritabilities of SCC traits, including lactation-mean SCS (SCS_LM), ranged from 0.038 to 0.136. Genetic correlations between SCC traits were moderate to strong, with very few exceptions. Unfavourable genetic associations between milk yield and SCS_SD and Infection indicated that high-producing cows were more susceptible to variation in SCC than low-producing animals. Cows with deep udders, loose attachments, weak ligaments and long teats were more susceptible to an increase of SCC in milk. Overall, results suggest that alternative SCC traits can be exploited to improve cow's resistance to mastitis in Italian Jersey breed.
Highlights
A strategy to improve genetic selection for disease resistance is to exploit the information routinely collected during milk recording procedures
Our results demonstrated strong genetic correlations be‐ tween somatic cell count (SCC) traits, with the only exception of SCS_SD, which was moderately correlated with traits indicating the presence of SCC peaks in the lactation (i.e. Infection and Severity) and uncorrelated with traits expressing mean values (SCS_LM and SCS_150)
Alternative SCC traits analysed in this study expressed exploitable genetic variation for breeding purposes
Summary
A strategy to improve genetic selection for disease resistance is to exploit the information routinely collected during milk recording procedures. Results of the above‐mentioned study contributed to define a novel udder health index in the Italian Holstein breed (Finocchiaro et al, 2018), in support of the current one which is based on TD SCS. The aim of this study was to define alternative SCC traits, derived from routine TD recording system, in Italian Jersey cows and to estimate their genetic relationships with milk yield, composition and udder type traits. Findings of this work will provide additional information to develop a udder health index aimed to improve resistance to mas‐ titis in Italian Jersey breed
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