Biomedical subjects

Rachel Rupp

Publications and source records attributed to Rachel Rupp.

6 recordsLinked to original sources

PubMed2005

Genotype-level variation in lifetime breeding success, litter size and survival of sheep in scrapie-affected flocks.

Five different sheep flocks with natural outbreaks of scrapie were examined to determine associations between individual performance (lifetime breeding success, litter size and survival) and scrapie infection or PrP genotype. Despite different breed composition and forces of infection, consistent patterns were found among the flocks. Regardless of the flock, scrapie-infected sheep produced on average 34 % fewer offspring than non-scrapie-infected sheep. The effect of scrapie on lifetime breeding success appears to be a function of lifespan as opposed to fecundity. Analysis of litter size revealed no overall or genotype differences among the five sheep flocks. Survival, however, depends on the individual's scrapie status (infected or not) and its PrP genotype. Susceptible genotypes appear to perform less well in lifetime breeding success and life expectancy even if they are never affected with clinical scrapie. One possible explanation for these results is the effect of pre-clinical scrapie. Additional evidence supporting this hypothesis is discussed.

Animals↗

PubMed2005

Polygenic variation and transmission factors involved in the resistance/susceptibility to scrapie in a Romanov flock.

Data from 4049 Romanov sheep belonging to a flock affected by natural scrapie were analysed by using survival-analysis techniques. Failure time was defined as the period of time between first exposure to infection and the date that animals left the flock with scrapie signs. Four hundred and forty-seven sheep were identified as 'scrapie animals'. Several models, including level of exposure as a time-dependent effect, PrP genotype, sex, age at first exposure, litter size and factors related to vertical transmission, were tested. The best model was extended to a sire-dam frailty model, in order to estimate the polygenic variation in addition to that in the Prnp gene. A combined effect of rearing type and the dam's disease status was detected. Thus, only sheep with a low degree of exposure to infection as lambs (lambs reared artificially and born out of a healthy dam) showed less risk than others. Animals first exposed to infection at older ages seemed to be less susceptible to scrapie. In this Romanov population, new genotypes (AHQ/AHQ, AHQ/VRQ, ARR/VRQ and ARR/ARQ) were associated with risk, suggesting the effect of genotypes on the incubation period of animals. Polygenic variance was responsible for 21 % of the total genetic variability that was related to susceptibility to scrapie. Therefore, the genetic susceptibility to scrapie may be explained by the joint effect of point mutations at the Prnp major gene and a number of genes that modulate its effect.

Aging↗

PubMedDate not supplied

Genetics of resistance to mastitis in dairy cattle.

Genetic variability of mastitis resistance is well established in dairy cattle. Many studies focused on polygenic variation of the trait, by estimating heritabilities and genetic correlation among phenotypic traits related to mastitis such as somatic cell counts and clinical cases. The role of Major Histocompatibility Complex in the susceptibility or resistance to intrammamary infection is also well documented. Finally, development from molecular genome mapping led to accumulating information of quantitative trait loci (QTL) related to mastitis resistance and better understanding of the genetic determinism of the trait. From economic and genetic analyses, and according to welfare and food safety considerations and to breeders and consumer's concern, there is more and more evidence that mastitis should be included in breeding objective of dairy cattle breeds. Many countries have implemented selection for mastitis resistance based on linear decrease of somatic cell counts. Given biological questioning, potential unfavourable consequences for very low cell counts cows are regularly investigated. Improvement of selection accuracy for mastitis resistance is ongoing and includes: advances in modelling, optimal combination of mastitis related traits and associated predictors, such as udder morphology, definition of global breeding objective including production and functional traits, and inclusion of molecular information that is now available from QTL experiments.

Animals↗

PubMedDate not supplied

Mastitis of dairy small ruminants.

Staphylococci are the main aetiological agents of small ruminants intramammary infections (IMI), the more frequent isolates being S. aureus in clinical cases and coagulase negative species in subclinical IMI. The clinical IMI, whose annual incidence is usually lower than 5%, mainly occur at the beginning of machine milking and during the first third of lactation. These features constitute small ruminant peculiarities compared to dairy cattle. Small ruminant mastitis is generally a chronic and contagious infection: the primary sources are mammary and cutaneous carriages, and spreading mainly occurs during milking. Somatic cell counts (SCC) represent a valuable tool for prevalence assessment and screening, but predictive values are better in ewes than in goats. Prevention is most often based on milking machine management, sanitation and annual control, and milking technique optimisation. Elimination mainly relies on culling animals exhibiting clinical, chronic and recurrent IMI, and on drying-off intramammary antibiotherapy; this treatment allows a good efficacy and may be used selectively by targeting infected udders only. Heritability values for lactation mean SCC scores are between 0.11 and 0.15. Effective inclusion of ewe's mastitis resistance in the breeding goal has recently been implemented in France following experimental and large scale estimations of genetic parameters for SCC scores.

Animals↗

PubMedDate not supplied

Detection of genes influencing economic traits in three French dairy cattle breeds.

A project of QTL detection was carried out in the French Holstein, Normande, and Montbéliarde dairy cattle breeds. This granddaughter design included 1 548 artificial insemination bulls distributed in 14 sire families and evaluated after a progeny-test for 24 traits (production, milk composition, persistency, type, fertility, mastitis resistance, and milking ease). These bulls were also genotyped for 169 genetic markers, mostly microsatellites. The QTL were analysed by within-sire linear regression of daughter yield deviations or deregressed proofs on the probability that the son receives one or the other paternal QTL allele, given the marker information. QTL were detected for all traits, including those with a low heritability. One hundred and twenty QTL with a chromosome-wise significance lower than 3% were tabulated. This threshold corresponded to a 15% false discovery rate. Amongst them, 32 were genome-wise significant. Estimates of their contribution to genetic variance ranged from 6 to 40%. Most substitution effects ranged from 0.6 to 1.0 genetic standard deviation. For a given QTL, only 1 to 5 families out of 14 were informative. The confidence intervals of the QTL locations were large and always greater than 20 cM. This experiment confirmed several already published QTL but most of them were original, particularly for non-production traits.

Animals↗

PubMedDate not supplied

Using genotype probabilities in survival analysis: a scrapie case.

The objective was to evaluate the potential use of genotype probabilities to handle records of non-genotyped animals in the context of survival analysis. To do so, the risks associated with the PrP genotype and other transmission factors in relation to clinical scrapie were estimated. Data from 4049 Romanov sheep affected by natural scrapie were analyzed using survival analysis techniques. The original data set included 1310 animals with missing genotypes; five of those had uncensored records. Different missing genotype-information patterns were simulated for uncensored and censored records. Three strategies differing in the way genotype information was handled were tested. Firstly, records with unknown genotypes were discarded (P1); secondly, those records were grouped in an unknown class (P2). Finally the probabilities of genotypes were assigned (P3). Whatever the strategy, the ranking of relative risks for the most susceptible genotypes (VRQ-VRQ, ARQ-VRQ and ARQ-ARQ) was similar even when the non-genotyped animals were not a negligible part of uncensored records. However, P3 had a more efficient way of handling missing genotype information. As compared to P1, either P2 or P3 avoided discarding the records of non-genotyped animals; however, P3 eliminated the unknown class and the risk associated with this group. Genotype probabilities were shown to be a useful technique to handle records of individuals with unknown genotype.

Animals↗