Genetic parameters for rennet- and acid-induced coagulation properties in milk from Swedish Red dairy cows

Abstract

Milk coagulation is an important processing trait, being the basis for production of both cheese and fermented products. There is interest in including technological properties of these products in the breeding goal for dairy cattle. The aim of the present study was therefore to estimate genetic parameters for milk coagulation properties, including both rennet- and acid-induced coagulation, in Swedish Red dairy cattle using genomic relationships. Morning milk samples and blood samples were collected from 395 Swedish Red cows that were selected to be as genetically unrelated as possible. Using a rheometer, milk samples were analyzed for rennet- and acid-induced coagulation properties, including gel strength (G'), coagulation time, and yield stress (YS). In addition to the technological traits, milk composition was analyzed. A binary trait was created to reflect that milk samples that had not coagulated 40min after rennet addition were considered noncoagulating milk. The cows were genotyped by using the Illumina BovineHD BeadChip (Illumina Inc., San Diego, CA). Almost 600,000 markers remained after quality control and were used to construct a matrix of genomic relationships among the cows. Multivariate models including fixed effects of herd, lactation stage, and parity were fitted using the ASReml software to obtain estimates of heritabilities and genetic and phenotypic correlations. Heritability estimates (h(2)) for G' and YS in rennet and acid gels were found to be high (h(2)=0.38-0.62) and the genetic correlations between rennet-induced and acid-induced coagulation properties were weak but favorable, with the exception of YSrennet with G'acid and YSacid, both of which were strong. The high heritability (h(2)=0.45) for milk coagulating ability expressed as a binary trait suggests that noncoagulation could be eliminated through breeding. Additionally, the results indicated that the current breeding objective could increase the frequency of noncoagulating milk and lead to deterioration of acid-induced coagulation through unfavorable genetic associations with protein content (0.38) and milk yield (-0.61 to -0.71), respectively. The outcome of this study suggests that by including more detailed compositional traits genetically associated with milk coagulation or by including milk coagulation properties directly within the breeding goal, it appears possible to breed cows that produce milk better suited for production of cheese and fermented products.

Mapping and fine-mapping of genetic factors affecting bovine milk composition

“…In addition, MCP seem be influenced by many factors, such as SCC (e.g., Ikonen et al, 2004;Cassandro et al, 2008), titratable acidity (e.g., Penasa et al, 2010), casein composition (Okigbo et al, 1985b), pH (Nájera et al, 2003), stage of lactation (Okigbo et al, 1985a;Ostersen et al,1997), and breed (e.g., Auldist et al, 2004;De Marchi et al, 2007, Bittante et al, 2012, among many other factors. Heritability estimates for MCP and NC milk range from 0.26 in FAY (Ikonen et al, 2004) to 0.45 in SR cows (Gustavsson et al, 2014a). These heritability estimates suggest that breeding could effectively reduce the prevalence of NC milk.…”

“…In Sweden, the breeding program includes production traits to guarantee the increase in both protein and fat contents (Nordic Cattle Genetic Evaluation, 2013). The negative genetic correlations between NC milk and protein content estimated by Gustavsson et al (2014a) suggest that breeding for higher protein content in the Swedish Red cows can lead to an increase in the prevalence of NC milk. In Sweden, 41% of SR cows produce milk for the dairy industry, and more than 30% of total milk production is used for cheese production (LRF Dairy Sweden, 2015).…”

“…The addition of the chymosin represented time zero. Measurements, such as rennet gel strength, rennet coagulation time, and yield stress of rennet-induced gels, were done and described by Gustavsson et al (2014a). Some samples were unable to coagulate within 40 min after rennet-addition, and were defined as non-coagulating (NC) milk samples.…”

“…Non-coagulating (NC) milk is prevalent among several dairy cattle breeds, such as Swedish Red (SR), Finnish Ayrshire (FAY), Holstein-Friesian (HF) and Italian Brown Swiss, to name a few (e.g., Frederiksen et al, 2011;, Gustavsson et al, 2014a. The prevalence of NC milk varies among these breeds ranging from 4% in Italian Brown Swiss (Cecchinato et al, 2009) up to 13% in FAY (Ikonen et al, 2004).…”

“…The prevalence of NC milk varies among these breeds ranging from 4% in Italian Brown Swiss (Cecchinato et al, 2009) up to 13% in FAY (Ikonen et al, 2004). A recent study has estimated the prevalence of NC milk, defined as milk not coagulating within 40 min after rennetaddition, at 18% in the SR cow population (Gustavsson et al, 2014a). Targeted research on NC milk can help geneticists develop breeding programs to modify milk composition and technological properties of milk and thus reduce the prevalence of NC milk.…”