title: Effect of CSN1S1-CSN3 (α(S1)-κ-casein) composite genotype on milk production traits and milk coagulation properties in Mediterranean water buffalo.
abstract: The aim of this study was to estimate effects of CSN1S1-CSN3 (α(S1)-κ-casein) composite genotypes on milk production traits and milk coagulation properties (MCP) in Mediterranean water buffalo. Genotypes at CSN1S1 and CSN3 and coagulation properties [rennet clotting time (RCT), curd firming time (K₂₀), and curd firmness (A₃₀)] were assessed by reversed-phase HPLC and computerized renneting meter analysis, respectively, using single test-day milk samples of 536 animals. Alternative protein variants of α(S1)-CN and κ-CN were detected by HPLC, and identification of the corresponding genetic variants was carried out by DNA analysis. Two genetic variants were detected at CSN1S1 (A and B variants) and 2 at CSN3 (X1 and X2 variants). Statistical inference was based on a linear model including the CSN1S1-CSN3 composite genotype effect (7 genotypes), the effects of herd-test-day (8 levels), and a combined days in milk (DIM)-parity class. Composite genotype AB-X2X2 was associated with decreased test-day milk yield [-0.21 standard deviation (SD) units of the trait] relative to genotype BB-X2X2. Genotypes did not affect milk protein content, but genotype AB-X1X1 was associated with increased fat content compared with genotype BB-X2X2 (+0.28 SD units of the trait) and AB-X1X1 (+0.43 SD units of the trait). For RCT, the largest difference (+1.91 min; i.e., 0.61 SD units of the trait) was observed between genotype AA-X1X2 and AB-X1X1. Direction of genotype effects on K(20) was consistent with that for RCT. The maximum variation in K₂₀ due to genotype effects (between AA-X1X2 and AB-X1X1 genotypes) was almost 0.9 SD units of the trait. Magnitude of genotype effects was smaller for A₃₀ than for RCT and K₂₀, with a maximum difference of 0.5 SD units of the trait between genotype AA-X1X2 and AA-X1X1. The B allele at CSN1S1 was associated with increased RCT and K₂₀ and with weaker curds compared with allele A. Allele X2 at CSN3 exerted opposite effects on MCP relative to CSN1S1 B. Because of linkage disequilibrium, allele B at CSN1S1 and allele X2 at CSN3 tend to be associated and this likely makes their effects cancel each other. This study indicates a role for casein genes in variation of MCP of buffalo milk. Further studies are necessary to estimate the effects of casein genetic variants on variation of cheese yield.
authors.affiliation: Department of Comparative Biomedicine and Food Science, University of Padova, viale dell'Università 16, 35020 Legnaro, Padova, Italy.
authors.forename: V
authors.initials: V
authors.lastname: Bonfatti
authors.forename: M
authors.initials: M
authors.lastname: Giantin
authors.forename: M
authors.initials: M
authors.lastname: Gervaso
authors.forename: A
authors.initials: A
authors.lastname: Coletta
authors.forename: M
authors.initials: M
authors.lastname: Dacasto
authors.forename: P
authors.initials: P
authors.lastname: Carnier
mesh_terms: D000483:Alleles; D000818:Animals; D002020:Buffaloes / Q000235:genetics* / Q000502:physiology; D002364:Caseins / Q000235:genetics*; D012085:Chymosin / Q000737:chemistry; D005260:Female; D005787:Gene Frequency / Q000235:genetics; D056726:Genetic Association Studies; D005838:Genotype; D007774:Lactation / Q000235:genetics*; D008892:Milk / Q000737:chemistry* / Q000592:standards; D011110:Polymorphism, Genetic / Q000235:genetics; D017422:Sequence Analysis, DNA / Q000662:veterinary
chemical_list: D002364:Caseins; C025350:rennet; D012085:Chymosin