Relación de las variantes A y B de la β-lactoglobulina con la producción y composición de la leche de vacas Holstein y criollo lechero tropical

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Abstract

Las variantes genéticas de la β-lactoglobulina (β-LG) A y B se han asociado con la producción y composición de la leche, lo que puede variar entre razas lecheras. El objetivo del presente estudio fue determinar la relación de las variantes genéticas de β-LG con la composición y producción de la leche de vacas Holstein (H) y Criollo Lechero Tropical (CLT). Se caracterizaron 350 muestras de leche de vacas H y 64 de CLT. La información individual de los registros productivos y reproductivos de ambas razas fue recopilada. En cada muestra se determinó la composición química por espectroscopía de infrarrojo medio y el recuento de células somáticas (CCS) por citometría de flujo. Se realizó un análisis de varianza con modelos mixtos para estudiar el efecto del fenotipo de la β-LG sobre la composición química de la leche, CCS, producción de leche, grasa y proteína ajustada a 305 d y producción de leche al día del muestreo. En el modelo estadístico se incluyó el efecto aleatorio del padre de la vaca y los efectos fijos de hato-año-estación, fenotipo y número de parto, además de las covariables días en leche y edad de la vaca. Se encontró efecto significativo del fenotipo de la β-LG sobre la composición química de la leche. Los porcentajes de grasa, proteína, sólidos no grasos y sólidos totales fueron significativamente (p≤0.05) mayores en el fenotipo BB en ambas razas. La producción de leche ajustada a los 305 d fue superior (p ≤0.05) en el fenotipo AA de vacas H.

Translated abstract

Genetic variants of β-lactoglobulin (β-LG) A and B have been associated with milk production and composition, which can vary between dairy breeds. The aim of this study was to determine the relationship of genetic variants of β-LG with milk composition and production of Holstein cows (H) and Tropical Milking Criollo (TMC). Three hundred and fifty milk samples of H cows and 64 of TMC were characterized. Individual information on production and reproduction records of both breeds was collected. The chemical composition of each sample was determined by mid-infrared spectroscopy and somatic cell count (SCC) by flow cytometry. An analysis of variance was conducted with mixed models to study the effect of β-LG phenotype on the chemical composition of milk, SCC, milk production, fat and protein adjusted to 305 d and milk yield at the day of sampling. In the statistical model, the random effect of the cows father and the fixed effects herd-year-season, phenotype and number of birth were included, besides the covariates days in milk and cow age. β-LG phenotype was found to have a significant effect on chemical composition of milk. The percentage of fat, protein, nonfat and total solids were significantly (p≤0.05) higher in BB phenotype for both breeds. The milk yield/production fitted to 305 d was higher (p ≤0.05) for AA phenotype of H cows.

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Effects of milk protein variants on the protein composition of bovine milk.

Koen G C Weel, Jeroen M L Heck, H. Bovenhuis … (2009)

The effects of beta-lactoglobulin (beta-LG), beta-casein (beta-CN), and kappa-CN variants and beta-kappa-CN haplotypes on the relative concentrations of the major milk proteins alpha-lactalbumin (alpha-LA), beta-LG, alpha(S1)-CN, alpha(S2)-CN, beta-CN, and kappa-CN and milk production traits were estimated in the milk of 1,912 Dutch Holstein-Friesian cows. We show that in the Dutch Holstein-Friesian population, the allele frequencies have changed in the past 16 years. In addition, genetic variants and casein haplotypes have a major impact on the protein composition of milk and explain a considerable part of the genetic variation in milk protein composition. The beta-LG genotype was associated with the relative concentrations of beta-LG (A > B) and of alpha-LA, alpha(S1)-CN, alpha(S2)-CN, beta-CN, and kappa-CN (B > A) but not with any milk production trait. The beta-CN genotype was associated with the relative concentrations of beta-CN and alpha(S2)-CN (A(2) > A(1)) and of alpha(S1)-CN and kappa-CN (A(1) > A(2)) and with protein yield (A(2) > A(1)). The kappa-CN genotype was associated with the relative concentrations of kappa-CN (B > E > A), alpha(S2)-CN (B > A), alpha-LA, and alpha(S1)-CN (A > B) and with protein percentage (B > A). Comparing the effects of casein haplotypes with the effects of single casein variants can provide better insight into what really underlies the effect of a variant on protein composition. We conclude that selection for both the beta-LG genotype B and the beta-kappa-CN haplotype A(2)B will result in cows that produce milk that is more suitable for cheese production.

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Estimation of effects of single genes on quantitative traits.

Stephen Kennedy, Annelie Everts-van der Wind, P. M. Quinton (1992)

Studies involving the effects of single genes on quantitative traits may involve closed populations, selection may be practiced, and the quantitative trait of concern may also be influenced by background genes that are inherited in a polygenic manner. It is shown analytically that analysis of such data by ordinary least squares, the usual method of analysis, can lead to finding an excess of spurious significant effects of single genes, when no effect exists, for both randomly and directionally selected populations and can lead to bias in estimates of single-gene effects when selection has been practiced. The bias depends on heritability of the polygenic effects on the trait, selection intensity, mode of inheritance, magnitude of gene effect, gene frequency, and data structure. It is argued that when genotypes of individuals can be identified for all individuals with observations on the trait, use of mixed-model procedures under an animal model treating single-gene effects as fixed effects can provide unbiased estimates of single-gene effects and exact tests of associated hypotheses for pedigreed populations, even when selection is practiced. Results are illustrated through computer simulation.