Biomedical subjects

F Lescourret

Publications and source records attributed to F Lescourret.

18 recordsLinked to original sources

PubMed2005

Simulating genotypic variation of fruit quality in an advanced peach x Prunus davidiana cross.

Ecophysiological models are increasingly expected to describe genotypic variation within breeding populations. Accordingly, the ability of an ecophysiological model of peach to explain variation in fruit quality among 100 genotypes of a second backcross progeny derived from a clone of wild peach (Prunus davidiana) crossed with two commercial nectarine (Prunus persica) varieties was explored. Experimental measurements were carried out to calibrate the model for each genotype. The predictive quality of the model was tested on several independent datasets. The genotypic variation in dry and fresh growth of the fruit and the stone were effectively described by the model. Prediction of the amount of total sugar in flesh at maturity was accurate, whereas prediction of flesh dry matter content and total sugar concentration was suitable but less accurate. This approach and the results have allowed physiological processes to be ranked according to their contribution to the variation in fruit quality between genotypes. Fruit growth demand and the hydraulic conductance in the fruit were the main processes that explained the fruit quality variation. Shortcomings and further potential uses of the model are discussed.

Agriculture↗

PubMed2005

Analysing the genetic control of peach fruit quality through an ecophysiological model combined with a QTL approach.

Ecophysiological models are increasingly expected to include genetic information via genotype-dependent parameters. These parameters could be considered as quantitative traits and submitted to analysis. A pre-existing ecophysiological model of fruit quality was used and the distribution of the genotypic parameters in a second backcross population derived from a clone of a wild peach (Prunus davidiana) and commercial nectarine varieties (P. persica (L.) Batsch) was analysed. The correlations between the two years of experimentation were higher for the genotypic parameters than for the quality traits commonly studied by breeders. The correlations between the genotypic parameters and the quality traits were low. Quantitative trait loci (QTLs) for the genotypic key parameters of the ecophysiological model were detected by linear regression. Co-locations of QTLs for parameters were observed as well as co-locations of QTLs for parameters and quality traits. The ecophysiological model and the results of the QTL analysis were combined by substituting each parameter in the model by the sum of QTL effects. This combined model can simulate the behaviour of genotypes carrying diverse combinations of alleles. The quality of this combined model was moderately suitable, but had some shortcomings. Improvements are suggested and further use of this combined model as a tool for breeders is discussed.

Agriculture↗

PubMed2004

Analysis of genotypic variation in fruit flesh total sugar content via an ecophysiological model applied to peach.

A simulation model of the evolution of total sugar content ( C(TS)) in fruit was developed in order to describe the within- and between-genotype variation of C(TS) observed in a peach ( Prunus persica (L.) Batsch) breeding population. The parameter k defines the ratio of carbon used for synthesizing compounds other than sugars for each genotype. Model input variables are dry flesh growth rate and fresh flesh mass of fruit. We estimated k for 137 peach and nectarine genotypes derived from a clone of a wild peach ( Prunus davidiana) by three generations of crosses with commercial nectarine varieties. We tested the predictive quality of the model on independent datasets. Despite an underestimation of the observed C(TS), the correlation between observations and predictions was suitable (0.72). Spearman correlation coefficients between 2001 and 2002 for model input variables and parameter k were higher than for C(TS). None of the three components assimilation supply to the fruit, metabolism, or dilution, seemed to have a greater relative effect on C(TS) variation than the others. Indeed, C(TS) variation seemed to result from the balance between the three components. The interest of this approach, which consists of dissecting traits into components via an ecophysiological model, for breeding strategy and for sugar accumulation studies are discussed.

Biological Evolution↗

PubMed2004

Does variability in shoot carbon assimilation within the tree crown explain variability in peach fruit growth?

A three-dimensional model of radiative transfer and leaf gas exchange was used to quantify daily carbon (C) assimilation of all fruit-bearing shoots (FBS) in an early maturing 6-year-old peach tree (Prunus persica L. Batsch) with a heavy crop load. For a sample of FBS (n=36), growth of fruit and leafy shoots was measured every 1-2 weeks from 24 days after bloom (DAB) until harvest, between 93-101 DAB. The objective was to relate shoot C assimilation with harvested fruit mass for each shoot to test the hypothesis that variation in C supply contributes significantly to variation in fruit growth within and among FBS. Mean C assimilation of the sampled shoots was 0.07 g C fruit(-1) day(-1), but varied between 0.014 and 0.32 g C fruit(-1) day(-1). This indicates that C availability for fruit growth would have varied significantly among individual FBS if they were autonomous. Mean fruit dry mass on each FBS varied between 0.716 and 7.68 g C at harvest, and most of the variation originated among, not within, individual FBS. However, there were no correlations between the mean and standard deviation of fruit mass and fruit relative growth rate when each was plotted against shoot C assimilation, indicating that factors such as those regulating C demand of fruit, or C transfer among individual FBS, may be more important in controlling variability in fruit growth than intra-crown variability in shoot C assimilation. Under the study conditions, FBS were non-autonomous for C, because a model of fruit and leafy shoot growth was unable to reproduce the observed growth without supplementary contribution of C from shoots without fruit.

Carbon↗

PubMed2003

Changes in fruit sugar concentrations in response to assimilate supply, metabolism and dilution: a modeling approach applied to peach fruit (Prunus persica).

The influence of assimilate supply, metabolism and dilution on sugar concentrations in the mesocarp of peach (Prunus persica (L.) Batsch) fruit during the main stage of fruit enlargement was analyzed with the SUGAR model of Génard and Souty (1996). The model predicts the partitioning of carbon into sucrose, sorbitol, glucose and fructose in the mesocarp of peach fruit. Based on measured data and the model, we determined values for the relative rates of sugar transformation. These rates were constant, varied with time or varied with relative fruit growth rate, depending on the type of sugar. Equations were derived to describe these rates and incorporated into the SUGAR model. The model simulated the effects of changing assimilate supply and fruit volume on sugar concentrations. The set of equations for the SUGAR model was rewritten to include the three components influencing sugar concentrations: assimilate supply, metabolism and dilution. The sugar types differed in sensitivity to these components. Sucrose was highly sensitive to changes in assimilate supply and to the dilution effect; it was not subject to intense metabolic transformation. Sorbitol was the most important carbohydrate in fruit metabolism, which explains why the sorbitol concentration was always low despite the strong positive effect of assimilate supply. The reducing sugars constituted a transitory storage pool and their concentrations were closely related to metabolism.

Carbohydrates↗

PubMed2002

Ecophysiological analysis of genotypic variation in peach fruit growth.

Cultivated varieties generally differ greatly from wild genotypes of the same closely related species. However, the processes responsible for these differences have not been elucidated. To analyse variations in fruit mass, fruit growth was characterized in a peach cultivar, a wild related species non-cultivated, and four hybrids derived by crossing them. These genotypes offer a wide range of agronomic values. An ecophysiological model of peach fruit growth in dry mass was used. This model simulates carbon partitioning at the 'shoot-bearing fruit' level by considering three compartments: fruits, 1-year-old stems and leafy shoots. The experimental measurements showed considerable variation between genotypes for fruit mass at maturity, fruit growth and source activity. The parameters of the ecophysiological model for each genotype were estimated from experimental data,. The model made it possible to account for genotypic variations in fruit growth and for genotype x fruit load interactions. Using the model, it was shown that the main processes explaining fruit growth variations among the genotypes studied were differences in potential fruit growth.

Algorithms↗

PubMed2001

Variation in surface conductance to water vapor diffusion in peach fruit and its effects on fruit growth assessed by a simulation model.

Surface conductance to water vapor diffusion was measured in individual peach fruits (Prunus persica (L.) Batsch) and plotted as a function of fresh fruit mass for four cultivars. Surface conductance increased with fresh fruit mass, but the pattern differed with cultivar, and fruit-to-fruit variation occurred. Relationships between fruit mass and surface conductance were modeled by fitting mathematical equations to the data. The simulation model of Fishman and Génard (1998) was used to study dry mass and water components of fruit growth (1) when surface conductance varied with fruit size or was constant, and (2) when surface conductance values were high, moderate or low with respect to fruit mass. Increased surface conductance with fresh fruit mass resulted in fruit growth cessation. Fruits differing in surface conductance had similar dry mass. However, under well-watered conditions (stem water potential between -1 and -0.2 MPa), the water balance components of growth (osmotic and hydrostatic pressure, water potential and water balance) differed greatly and, as a result, the lower the surface conductance the greater the fresh fruit mass. These differences were buffered under drought conditions (stem water potential between -2.4 and -0.6 MPa).

Fruit↗

PubMed1997

Interrelationships between herd management practices and udder health status using canonical correspondence analysis.

The relationships between the herd-level distribution of udder health measures (traumatic, physical, functional and congestive udder disorders, clinical mastitis and somatic cell counts (SCC) greater than 400 x 10(3) ml-1) and farm (general hygiene, milking practices and housing system) and aggregated individual characteristics were studied by canonical correspondence analysis (CCA). This is a correspondence-analysis technique in which the axes representing disease patterns are expressed as linear combinations of potentially explanatory variables. These main axes can be drawn so that the distribution of diseases for combinations of the main-explanatory managerial variables can be visualized. The type of quarantine for newcomers, type of animal housing, presence of shelter at pasture, use of udder towel before milking, milk production and loss of body condition after calving, were strongly correlated with udder health status. Mastitis and physical udder disorders were associated with the combination of no introduction of replacement heifers and low loss of body condition after calving. Congestive disorders were more common on farms when no quarantine for newcomers was combined with high loss of body condition after calving. Higher clinical and subclinical mastitis incidence risks were associated with the combination of no udder towel, loose housing with high animal density and high milk production. In most cases, clinical mastitis and high SCC were explained by the same covariates but with contrasting levels of those covariates.

Animal Husbandry↗

PubMed1997

Factors affecting the distribution of clinical mastitis among udder quarters in French dairy cows.

Factors related to the distribution of clinical bovine mastitis between rear and front quarters were studied using data from a 4 year survey of commercial dairy herds in western France. The study involved 844 mastitis cases affecting 597 lactations of 500 French Friesian cows from 44 herds. Risk factor hypotheses were related to certain aspects of lactation, udder conformation and management practices. Distribution was modelled using a hierarchical logistic regression. Rear quarters were affected in 61.9% of cases. The only significant risk factor was the cow's parity; rear quarter clinical mastitis was more frequent in primiparous than in multiparous cows. In this retrospective study, udder conformation did not seem to play a significant role in mastitis distribution. No overdispersion parameter was observed, indicating that each mastitis case could be considered as an independent event.

Animals↗

PubMed1996

Effect of foot lesions on milk production by dairy cows.

Individual curves for milk production of 428 cows affected by foot lesions were compared with control curves drawn from data of healthy lactating cows. First, differences were classified into patterns of milk loss, and their distribution was analyzed among the patterns with regard to breed, season, parity, stage of lactation, and milk production. Then, individual milk losses were estimated and analyzed according to the same factors. During early lactation, as during mid to late lactation, no marked modifications of the lactation curves occurred for about one-half of the cases. In 25% of the cases, milk production was affected for an expanded period (medians were 17 wk for early lactation and 12 wk for mid to late lactation). Corresponding median milk losses were 440 and 270 kg, respectively. Summer foot lesions were more severe than winter lesions, regardless of stage of lactation. Milk production at foot lesion onset was a determining factor of the amount and pattern of milk loss only for cases occurring during mid to late lactation.

Animals↗

PubMed1996

A method for describing disease patterns during the life span of dairy cows.

This study presents some guidelines for describing the health status of dairy cows over their entire life span. It aims to define some types of health-paths (trajectories) described in terms of disease patterns (at the lactation level) and related to cow characteristics (breed, production potential) and farms. The data were collected over a 20-year period on three experimental farms. Eight diseases were analysed: clinical mastitis, lameness, placental retention, foot rot, digestive disorders, milk fever, metritis, and arthritis. The statistical procedures used were correspondence analysis of time-indexed tables and hierarchical ascending clustering. A total of 28 health-paths were identified and 16 of these (the most common) are described in detail. At the lactation level, eight disease patterns were defined: high incidence of disease other than mastitis (1), predominantly mastitis plus milk fever (2), predominantly foot rot (3), very low incidence of disease (4), mastitis plus digestive disorders (5), very high mastitis incidence (6), low incidence of disease (7), foot rot plus digestive disorders (8). Disease patterns 3 and 6 were more common in shorter life spans (< or = 4 lactations). Conversely, health profiles 2 and 4 were generally related to the longest life spans. These results will be included in a future model of the life span of dairy cows which will also take into account other performance parameters such as milk production and reproduction.

Aging↗

PubMed1995

Predictive model of mastitis occurrence in the dairy cow.

Mastitis occurrence within a lactation and times of mastitis onset were studied for about 1000 cows. The number of mastitis cases within a lactation was modeled through overdispersed Poisson regression with individual and herd covariants. The results emphasized the role of the herd variable. Increased production potential increased the number of cases per lactation at a rate of 1.4/10 kg. Calving month also played an important role. The incidence of mastitis was greater when calving took place in early autumn or winter, which led to an expanded housing period. The interval from calving to the first case of mastitis and the intervals between successive cases were modeled for cases occurring during lactation through random selections from fitted gamma distributions, these distributions being truncated to consider the lactation length. The results of both steps can be used to simulate mastitis occurrence in different conditions.

Animals↗

PubMed1994

Modeling the impact of mastitis on milk production by dairy cows.

Individual milk production curves of 542 cows with 722 cases of mastitis were compared with control curves drawn from healthy lactating cows. First, differences were classified into patterns of milk loss, and their distribution was analyzed among the patterns with regard to breed, season, lactation number, stage of lactation, and milk production. Then, individual milk losses were estimated and analyzed according to the same factors. In early lactation, almost 7% of mastitis cases necessitated culling or drying off. For 36% of the cases of mastitis occurring in early lactation, milk production was affected for an extended period, and the milk loss induced was 911 kg on average over the entire lactation. Fifty-two percent of the mastitis cases occurring after lactation peak was not accompanied by marked modifications of the lactation curves. For 38% of cases of mastitis occurring from mid to late lactation, milk production was affected for an extended period. When milk production was the most affected (26% of total cases), the average loss was 850 kg over the entire lactation. For cases in early or mid to late lactation, the production at mastitis onset was a determining factor of the amount and pattern of milk production loss induced. Results were applied in a simulation over two simulated groups of cows.

Animals↗

PubMed1994

[Modeling the information system of a research program using the MERISE method: the example of an ecopathological survey on dairy cows].

We present the MERISE method for the design of an information system, detailing data modelling. An exploratory research program on peri-partum pathology in intensive dairy herds is used as an example. The information system is divided into thematic subsystems called 'fields', which are represented by a global conceptual scheme. For each field, a detailed conceptual model is then determined through precise modelling guidelines. This division facilitates the validation of models by the partners of the project, and makes it possible to re-use the fields in other research programs.

Animals↗

PubMed1994

[Modelling of temporal data and the role of graphics].

The importance of graphics for temporal data modelling, which is often used in ecopathology, is illustrated through 2 examples. The first concerns a univariate time series (tank milk germ measurements). It uses correlograms (choice of the model), plots of residuals of the model (diagnostics) and principal component analysis graphical outputs (comparison of time series). The second concerns climate multivariate monthly time series. A 3-way analysis and graphical outputs are used to give a mark to each station, describing its climate for a set of months.

Analysis of Variance↗

PubMed1994

Farming practices associated with the 'udder infection' complex.

A total of 4,129 dairy cows from 47 dairy farms were submitted each year after calving to a milk sampling for bacteriological examination. Six criteria defined the udder infection complex: frequency of minor, major and rare pathogens; rate of clinical and subclinical mastitis; and index of gravity of mastitis. Forty-seven variables described practices and their associations with the type of farms (defined by the above 6 criteria) were studied. The associated variables were dipping practices, covering of the milking parlour, disinfection practices, housing cleanliness and milk production.

Animal Husbandry↗

PubMed1994

[Nutritional factors and mammary inflammatory infection in the dairy cow. Ecopathological approach during the peripartum period].

The relationships between nutrition and udder inflammation/infection were studied in the dairy cow using an ecopathological approach. The study ('enquête écopathologique Bretagne') was performed over 4 yr in French herds with high-lactating cows. A long distribution time of Italian ryegrass silage and a low quantity of dietary cereal-based concentrates in the first 2 months of lactation was linked with low milk leukocyte counts, probably due to a high dietary energetic level or to a polyunsaturated fatty acid imbalance and a subsequent decrease in the synthesis of leukotriene LTB4. In the late gestation period, a long distribution time of fresh English rye-grass, which induced high uraemia and a larger distribution of vitamins A, D and E, was related to lower frequencies of major pathogens in the milk.

Animal Feed↗

PubMed1994

[Trajectory types of health status during the life of the dairy cow].

This paper presents a first approach of the health over the whole life-cycle of dairy cows, a scale which is intended to define a trajectory. Trajectories are defined as the chain of health profiles on the lactation scale, which are characterized by major disorders: foul of the foot; lameness; arthritis; calving disorders; mastitis; digestive and metabolic disorders; and no disorders. A few examples of trajectories are discussed for life-cycles lasting 4 lactations.

Animals↗