Casein polymorphism and relation between milk production traits

• Published in: Journal of animal breeding and genetics (1986) 1999-04, Vol.116 (2), p.87-97
• Main Authors: Freyer, G, Liu, Z, Erhardt, G, Panicke, L
• Format: Article
• Language: English
• Subjects: APTITUD LECHERA; APTITUDE LAITIERE; CASEIN; CASEINA; CASEINE; CONTENIDO DE LIPIDOS; CONTENIDO PROTEICO; CORRELACION GENETICA; CORRELATION GENETIQUE; COW MILK; DAIRY COWS; GENETIC CORRELATION; GENETIC POLYMORPHISM; GENOTIPOS; GENOTYPE; GENOTYPES; LAIT DE VACHE; LECHE DE VACA; LIPID CONTENT; LOCI; LOCUS; MILK PERFORMANCE; POLIMORFISMO GENETICO; POLYMORPHISME GENETIQUE; PROTEIN CONTENT; TENEUR EN LIPIDES; TENEUR EN PROTEINES; VACAS LECHERAS; VACHE LAITIERE
• ISSN: 0931-2668; 1439-0388
• DOI: 10.1046/j.1439-0388.1999.00181.x

Introduction The trait relation between milk yield, fat yield and protein yield on one hand and protein percentage and fat percentage on the other is partly characterized by negative genetic correlation coefficients. Nevertheless, selection of high yielding cows in breeding of Holstein Friesian has been accompanied by approximately +1% of fat and nearly no gain in protein percentage during the last 30 years. The index selection involving yield and percentage of fat and protein simultaneously results in lower selection responses for each trait compared with single trait selection. Investigations of linkage of quantitative trait loci (QTL) for milk production traits to genetic markers could be useful for examining the genetic background for the specific trait relationship. The main focus is the detection of loci which are linked to QTL for a specific trait. The question arises whether identical or closely linked genes are responsible for the negative correlation between yield and percentage traits. It is rare for cows to be superior in both yield traits and percentage traits. The results of different studies regarding the casein locus on chromosome 6 suggest that this super locus has an effect on the performance ( Velmala et al. 1995 ; Vilkki 1996). The casein locus can thus be marked as was done by Graml et al. (1985) because almost no recombination occurs between the single loci. The location of the casein genes (αS1‐CN, β‐CN, κ‐CN) within the casein locus on chromosome 6 is known (e.g. Eggen & Fries 1995). The statistical analysis may be carried out in different ways. It ranges from analyses of variance ( anova), regressive models, the examination of differences in daughter performance of carriers of two paternal alleles (e.g. Kühn et al. 1996 ), maximum likelihood approaches to Gibbs sampling (e.g. Wild 1997). Liu (1994) reported significant QTL effects for milk yield and protein yield using the mixed model of inheritance. Simianer (1993) found a significant QTL effect for fat yield near the casein locus. The evidence of genetic linkage between genetic markers and putative QTL for single milk production traits was given in some family analyses. A significant linkage between QTL for milk yield, fat percentage and protein percentage and markers on chromosome 6 in one out of 14 families, using a major gene model, has been published by Georges et al. (1995) . Spelman et al. (1996) obtained evidence of a putative QTL for protein percentage in a loose linkage