Showing papers by "Roel F. Veerkamp published in 2004"

Genetic relationships among linear type traits, milk yield, body weight, fertility and somatic cell count in primiparous dairy cows

Abstract: Phenotypic and genetic (co)variances among type traits, milk yield, body weight, fertility and somatic cell count were estimated. The data analysed included 3,058 primiparous spring-calving Holstein-Friesian cows from 80 farms throughout the south of Ireland. Heritability estimates for the type traits varied from 0.11 to 0.43. Genetic correlations among some type traits were very strong and may indicate the possibility of reducing the number of traits assessed on each animal; the genetic correlation between angularity and body condition score was -0.84. Genetic correlations between all type traits (except body condition score, udder depth and teat length) and milk yield were positive and ranged from 0.08 to 0.69. The possibility of selecting for body weight may be achievable within a national progeny-testing programme using type traits within a selection index. Moderate to strong genetic correlations existed between some type traits and the various fertility measures and somatic cell count indicating the opportunity of indirect selection for improved fertility and health of animals using type traits within a selection index; however, the standard errors of some of the genetic correlations were large and should thus be treated with caution. Genetically taller, wider, deeper, more angular cows with tighter, stronger, shallower udders were predisposed to have inferior pregnancy rates to first service and require more services.

Effects of data structure on the estimation of covariance functions to describe genotype by environment interactions in a reaction norm model

Abstract: Covariance functions have been proposed to predict breeding values and genetic (co)variances as a function of phenotypic within herd-year averages (environmental parameters) to include genotype by environment interaction. The objective of this paper was to investigate the influence of definition of environmental parameters and non-random use of sires on expected breeding values and estimated genetic variances across environments. Breeding values were simulated as a linear function of simulated herd effects. The definition of environmental parameters hardly influenced the results. In situations with random use of sires, estimated genetic correlations between the trait expressed in different environments were 0.93, 0.93 and 0.97 while simulated at 0.89 and estimated genetic variances deviated up to 30% from the simulated values. Non random use of sires, poor genetic connectedness and small herd size had a large impact on the estimated covariance functions, expected breeding values and calculated environmental parameters. Estimated genetic correlations between a trait expressed in different environments were biased upwards and breeding values were more biased when genetic connectedness became poorer and herd composition more diverse. The best possible solution at this stage is to use environmental parameters combining large numbers of animals per herd, while losing some information on genotype by environment interaction in the data.

A missense mutation in the bovine leptin receptor gene is associated with leptin concentrations during late pregnancy

Abstract: The leptin receptor (LEPR) gene consists of 20 exons divided over 1.75 Mb. Parts of bovine LEPR exon 4 (79 bp), exon 11 (95 bp) and exon 20 (513 bp) of 20 cows (Holstein-Friesian) were sequenced (AJ580799; AJ580800; AJ580801) in an attempt to find polymorphisms. In exons 4 and 11 no SNPs were found. In exon 20, a T to C missense mutation was found at nucleotide 115, which causes an amino acid substitution at residue 945 (T945M). Frequencies for alleles C and T were 0.93 and 0.07 respectively, in a population of 323 Holstein-Friesian cows and TT animals were not detected. Using genotypes of these cows an association study was performed for leptin concentrations during late pregnancy and lactation. Leptin concentrations were determined by radioimmunoassay (RIA). The T945M mutation showed an association with circulating leptin concentrations only during late pregnancy (P 0.05). The CC genotype had higher concentrations than the CT genotype during this period. A combined effect with previously described leptin polymorphisms on prepartum leptin concentrations was observed, with one genotype combination having significantly lower levels of leptin up to 50 days, but interaction effects were not significant. The T945M polymorphism may have induced a structural change in the intracellular domain of the LEPR, which may have influenced the signal transduction pathway. However, the effect was found only for the heterozygous genotype because the TT genotype was not detected in this population of 323 Holstein-Friesian cows.