Derivation of multivariate indices of milk composition, coagulation properties, and individual cheese yield in dairy sheep

Abstract

Milk composition and its technological properties are traits of interest for the dairy sheep industry because almost all milk produced is processed into cheese. However, several variables define milk technological properties and a complex correlation pattern exists among them. In the present work, we measured milk composition, coagulation properties, and individual cheese yields in a sample of 991 Sarda breed ewes in 47 flocks. The work aimed to study the correlation pattern among measured variables and to obtain new synthetic indicators of milk composition and cheese-making properties. Multivariate factor analysis was carried out on individual measures of milk coagulation parameters; cheese yield; fat, protein, and lactose percentages; somatic cell score; casein percentage; NaCl content; pH; and freezing point. Four factors that were able to explain about 76% of the original variance were extracted. They were clearly interpretable: the first was associated with composition and cheese yield, the second with udder health status, the third with coagulation, and the fourth with curd characteristics. Factor scores were then analyzed by using a mixed linear model that included the fixed effect of parity, lambing month, and lactation stage, and the random effect of flock-test date. The patterns of factor scores along lactation stages were coherent with their technical meaning. A relevant effect of flock-test date was detected, especially on the 2 factors related to milk coagulation properties. Results of the present study suggest the existence of a simpler latent structure that regulates relationships between variables defining milk composition and coagulation properties in sheep. Heritability estimates for the 4 extracted factors were from low to moderate, suggesting potential use of these new variables as breeding goals.

Estimates of heritability and genetic correlations for milk coagulation properties and individual laboratory cheese yield in Sarda ewes

“…Fat, protein and casein percentages (Table 2) were similar to those observed in individual data either in Sarda (Pazzola et al, 2014;Manca et al, 2016) and in other Italian breeds, such as Valle del Belice (Cappio-Borlino et al, 1997), Massese (Martini et al, 2008) and alpine breeds (Bittante et al, 2014). Milk solid were lower than those reported for Spanish breeds (Othmane et al, 2002;Jaramillo et al, 2008).…”

“…RCT is the time between rennet addition and the start of the milk coagulation, k20 is the time at which the typical oscillation graph reaches the width of 20 mm, and a30 is the width of the graph at 30 min after rennet addition. ILCY was determined according to a modified method of Othmane et al, (2002), further details of the methodology used are provided in Manca et al, (2016). The predicted pecorino cheese yield (PPCY) was also calculated using the equation proposed by Pirisi et al, (1994): PPCY = 1.747 x protein% + 1.272 x fat%.…”

Genome-wide association and pathway-based analysis using latent variables related to milk protein composition and cheesemaking traits in dairy cattle

“…Using FA, we condensed 26 cheesemaking phenotypes into 10 F. Although the average KMO value was not high, it was close to the value reported in a recent and similar study on milk composition, MCP, and udder health phenotypes in dairy sheep (Manca et al, 2016). The 10 F in our study represented basic concepts of the cheesemaking process, retaining 74% of the original variability.…”

Use of multivariate factor analysis to characterize the fatty acid profile of buffalo milk

“…Multivariate factor analysis (MFA) is particularly suitable for studying and interpreting complex multivariate systems through the extraction of few variables (latent factors) with clear technical and biological meaning Manca et al, 2016;Mele et al, 2016). Furthermore factor scores could be used as new phenotypes for further analyses.…”