Phenotypic and genetic parameter estimates of cheese-making traits and their relationships with milk production, composition and functional traits in Spanish Assaf sheep

Sheep milk is mostly used for the production of cheese. In this study, a commercial population of Spanish Assaf sheep was analyzed for six cheese-making traits: four related to milk-coagulation properties (MCPs) [rennet coagulation time (RCT), curd-firming time (K-20), and curd firmness at minutes 30 and 60 (A(30), A(60))] and two related to cheese yield [individual laboratory cheese yield (ILCY) individual laboratory dried curd yield (ILDCY)]. Records for milk production traits were also available for this study. Restricted maximum likelihood (REML) analysis was used to estimate the genetic parameters and variance components, whereas bivariate models were used to calculate the phenotypic and genetic correlations among the traits considered in this work. Of the 1,143 milk samples included in the study, 147 (13%) did not coagulate, whereas 425 samples (approximately 37%) showed slow coagulation (samples with a record for A(60) and a missing record for A(30)). Also, large mean values were observed for RCT (29.54 min) and logK(20) (1.35 min). The heritabilities estimated for the cheese-making traits were moderate, ranging between 0.15 (for ILDCY) and 0.30 (A30 and ILCY). In general, within the pairs of related cheese-making traits, we found moderate-high phenotypic and genetic correlations. The RCT and logK20 traits showed high negative correlations with A30 and A60 at both the genetic and phenotypic levels. From the estimation of genetic parameters among these and several milk traits, the high and positive genetic correlations observed between PP and the two cheese yield traits should be highlighted. Based on the estimated phenotypic correlations, our study supports that subclinical mastitis is related to a delayed gelification of milk and lower curd firmness. Overall, this study provides the first report about the phenotypic and genetic parameters of cheese-making traits in a commercial population of Assaf sheep, offering preliminary information that might help to identify the cheese-making or related milk production traits that could be considered to improve Assaf population toward enhanced cheese performance features.