Estimation of genetic parameters for cheese-making traits in Spanish Churra sheep

Abstract

The global production of sheep milk is growing, and the main industrial use of sheep milk is cheese making. The Spanish Churra sheep breed is one of the most important native dairy breeds in Spain. The present study aimed to estimate genetic parameters for a wide range of traits influencing the cheese-making ability of Churra sheep milk. Using a total of 1,049 Churra ewes, we studied the following cheese-making traits: 4 traits related to milk coagulation properties (rennet coagulation time, curd-firming time, and curd firmness at 30 and 60 min after addition of rennet), 2 traits related to cheese yield (individual laboratory cheese yield and individual laboratory dried curd yield), and 3 traits measuring curd firmness over time (maximum curd firmness, time to attain maximum curd firmness, and syneresis). In addition, a list of milk traits, including the native pH of the milk and several milk production and composition traits (milk yield; the fat, protein, and dried extract percentages; and the somatic cell count), were also analyzed for the studied animals. After discarding the noncoagulating samples (only 3.7%), data of 1,010 ewes were analyzed with multiple-trait animal models by using the restricted maximum likelihood method to estimate (co)variance components, heritabilities, and genetic correlations. In general, the heritability estimates were low to moderate, ranging from 0.08 (for the individual laboratory dried curd yield trait) to 0.42 (for the fat percentage trait). High genetic correlations were found within pairs of related traits (i.e., 0.93 between fat and dried extract percentages, −0.93 between the log of the curd-firming time and curd firmness at 30 min, 0.70 between individual laboratory cheese yield and individual laboratory dried curd yield, and −0.94 between time to attain maximum curd firmness and syneresis). Considering all the information provided here, we suggest that in addition to the current consideration of the protein percentage trait for improving cheese yield traits, the inclusion of the pH of milk as a measured trait in the Churra dairy breeding program would represent an efficient strategy for improving the cheese-making ability of milk from this breed.

Genome-wide association studies (GWAS) and post-GWAS analyses for technological traits in Assaf and Churra dairy breeds

“…Moreover, to our knowledge, there are no studies that combine analyses of GWAS for milk and cheese-making traits in 2 different dairy breeds. Different breeds show different behaviors concerning MCP (Pazzola et al, 2014a;Pelayo et al, 2021). In particular, concerning Assaf and Churra sheep, previous studies performed by our research group have identified clear differences between both breeds regarding MCP.…”

“…The phenotypic data used in this study were previously described by Sánchez-Mayor et al (2019) for the Assaf breed and by Pelayo et al (2021) for the Churra breed. A total of 2,020 ewes belonging to the Assaf (n = 1,039, number of flocks = 4) and Churra breeds (n = 981, number of flocks = 2) were analyzed.…”

“…Concerning the cheese yield, the individual laboratory cheese yield (ILCY, g/10 mL of milk) and the individual laboratory dried curd yield (ILDCY, g/10 mL) were estimated following Othmane et al (2002a,c). The genetic parameters estimated for all the traits presented in this work (both milk and cheesemaking traits) were previously analyzed by Sánchez-Mayor et al (2019) for the Assaf breed and by Pelayo et al (2021) for the Churra breed. Note that in these 2 studies, after the initial assessment of the normality of the variable distributions for each trait, logarithmic base 10 transformations of the K 20 and SCC traits were considered for the different analyses (logK 20 ; logSCC).…”

“…Some of the most studied indicators related to cheese-making ability are traits related to milk coagulation properties (MCP; McMahon and Brown, 1982;Bynum and Olson, 1982) and different measurements of cheese yield (Othmane et al, 2002a,c). Toward a better understanding of the genetic basis of cheese-making traits in dairy sheep, our research group has recently investigated the genetic parameters for 2 groups of traits characterizing the technological behavior of milk (MCP and cheese yield) in 2 of the main dairy sheep breeds in Spain, namely, the Assaf and Churra breeds (Sánchez-Mayor et al, 2019;Pelayo et al, 2021). However, the lack of a straightforward methodology to routinely measure cheese yield-related traits at farms has hampered the integration of these traits into classical breeding programs.…”

“…In particular, concerning Assaf and Churra sheep, previous studies performed by our research group have identified clear differences between both breeds regarding MCP. Milk from Churra shows shorter coagulation times than milk from Assaf (Sánchez-Mayor et al, 2019;Pelayo et al, 2021). Thus, identifying unique and common genomic regions among breeds associated with cheese-related traits could provide insights into the genetic basis of the milk coagulation process in sheep.…”