ABSTRACT
This study aimed to estimate the heritability of milk yield (MY), fat percent (F%), fat yield (FY), protein percent (P%), protein yield (PY), somatic cell score (SCS), and total bacterial count score (TBCS) as well as to estimate the genetic correlations among these traits, using a dataset from 5,918 lactations of Jersey cows in Brazil. The covariance components were estimated by restricted maximum likelihood using the PEST and VCE6 programs. The average values obtained for MY, F%, FY, P%, PY, SCS, and TBCS were 5017.5 kg, 4.3%, 192.3 kg, 3.3%, 173.0 kg, 5.9, and 2.9, respectively, while the heritability values were 0.16, 0.55, 0.18, 0.61, 0.25, 0.21, and 0.08, respectively. The genetic correlations ranged from low to high magnitude, with positive values from 0.06 (TBCS-PY) to 0.72 (FY-PY), and negative values from −0.04 (F%-TBCS) to −0.44 (P%-TBCS). The Jersey breed from Brazil shows genetic variability for all traits analyzed in the present study, and our results suggest that higher genetic gain will be achieved when F% and P% are used as selection criteria. In addition, it is important to use SCS as a selection criterion since the selection for MY and PY may lead to higher SCS or TBCS values, which are undesirable. This was the first study to estimate genetic parameters for milk quality (PY, P%, FY, F%) and udder health (SCS, TBCS) traits in Jersey cows from Brazil. This information is useful for breeding schemes and contributes to better characterize these parameters in tropical region, since few studies were developed with the Jersey cattle in this environment.
Key Words:
genetic correlation; heritability; mastitis resistance; selection
