title: Longitudinal data analysis of polymorphisms in the κ-casein and β-lactoglobulin genes shows differential effects along the trajectory of the lactation curve in tropical dairy goats.
abstract: The κ-casein (CSN-3) and β-lactoglobulin (BLG) genes are extensively polymorphic in ruminants. Several association studies have estimated the effects of polymorphisms in these genes on milk yield, milk composition, and cheese-manufacturing properties. Usually, these results are based on production integrated over the lactation curve or on cross-sectional studies at specific days in milk (DIM). However, as differential expression of milk protein genes occurs over lactation, the effect of the polymorphisms may change over time. In this study, we fitted a mixed-effects regression model to test-day records of milk yield and milk quality traits (fat, protein, and total solids yields) from Colombian tropical dairy goats. We used the well-characterized A/B polymorphisms in the CSN-3 and BLG genes. We argued that this approach provided more efficient estimators than cross-sectional designs, given the same number and pattern of observations, and allowed exclusion of between-subject variation from model error. The BLG genotype AA showed a greater performance than the BB genotype for all traits along the whole lactation curve, whereas the heterozygote showed an intermediate performance. We observed no such constant pattern for the CSN-3 gene between the AA homozygote and the heterozygote (the BB genotype was absent from the sample). The differences among the genotypic effects of the BLG and the CSN-3 polymorphisms were statistically significant during peak and mid lactation (around 40-160 DIM) for the BLG gene and only for mid lactation (80-145 DIM) for the CSN-3 gene. We also estimated the additive and dominant effects of the BLG locus. The locus showed a statistically significant additive behavior along the whole lactation trajectory for all quality traits, whereas for milk yield the effect was not significant at later stages. In turn, we detected a statistically significant dominance effect only for fat yield in the early and peak stages of lactation (at about 1-45 DIM). The longitudinal analysis of test-day records allowed us to estimate the differential effects of polymorphisms along the lactation curve, pointing toward stages that could be affected by the gene.
authors.affiliation: Grupo de Investigación en Genética, Mejoramiento y Modelación Animal (GaMMA), Facultad Ciencias Agrarias, Universidad de Antioquia, Calle 67, no 53-108, AA 1226, Medellín, Colombia 005043.
authors.forename: Samir Julián Calvo
authors.initials: SJC
authors.lastname: Cardona
authors.affiliation: Grupo de Investigación en Genética, Mejoramiento y Modelación Animal (GaMMA), Facultad Ciencias Agrarias, Universidad de Antioquia, Calle 67, no 53-108, AA 1226, Medellín, Colombia 005043.
authors.forename: Henry Cardona
authors.initials: HC
authors.lastname: Cadavid
authors.affiliation: Facultad Ciencias Agropecuarias, Universidad de La Salle, Bogotá, Colombia 110231; Departamento de Producción, Facultad de Agronomía, Universidad de Buenos Aires, San Martín 4453 (1417), Ciudad Autónoma de Buenos Aires, Argentina.
authors.forename: Juan David
authors.initials: JD
authors.lastname: Corrales
authors.affiliation: Departamento de Producción, Facultad de Agronomía, Universidad de Buenos Aires, San Martín 4453 (1417), Ciudad Autónoma de Buenos Aires, Argentina.
authors.forename: Sebastián
authors.initials: S
authors.lastname: Munilla
authors.affiliation: Departamento de Producción, Facultad de Agronomía, Universidad de Buenos Aires, San Martín 4453 (1417), Ciudad Autónoma de Buenos Aires, Argentina; Unidad Ejecutora de Investigaciones en Producción Animal (INPA), Universidad de Buenos Aires - Consejo Nacional de Investigaciones Científicas y Técnicas, Cdad. Atma. Buenos Aires (1417), Argentina.
authors.forename: Rodolfo J C
authors.initials: RJC
authors.lastname: Cantet
authors.affiliation: Departamento de Producción, Facultad de Agronomía, Universidad de Buenos Aires, San Martín 4453 (1417), Ciudad Autónoma de Buenos Aires, Argentina; IGEVET-Instituto de Genética Veterinaria "Ing. Fernando Noel Dulout" (UNLP - CONICET La Plata), Facultad de Ciencias Veterinarias, Universidad Nacional de La Plata, Calle 60 y 118 S/N, La Plata, Argentina 1900. Electronic address: arogberg@agro.uba.ar.
authors.forename: Andrés
authors.initials: A
authors.lastname: Rogberg-Muñoz
mesh_terms: D000818:Animals; D002364:Caseins / Q000235:genetics* / Q000378:metabolism; D003430:Cross-Sectional Studies; D005260:Female; D005838:Genotype; D060005:Genotyping Techniques; D006041:Goats / Q000235:genetics*; D007774:Lactation / Q000235:genetics*; D007782:Lactoglobulins / Q000235:genetics / Q000378:metabolism; D008137:Longitudinal Studies; D008892:Milk / Q000737:chemistry / Q000378:metabolism; D010641:Phenotype; D020641:Polymorphism, Single Nucleotide; D040641:Quantitative Trait Loci
chemical_list: D002364:Caseins; D007782:Lactoglobulins
keywords: additive; dairy goats; dominance; longitudinal data; β-lactoglobulin; κ-casein