Biomedical subjects

V Ducrocq

Publications and source records attributed to V Ducrocq.

27 records · Page 2Linked to original sources

PubMed1999

Conjugal transfer of a TOL-like plasmid and extension of the catabolic potential of Pseudomonas putida F1.

Strain mX was isolated from a petrol-contaminated soil, after enrichment on minimal medium with 0.5% (v/v) meta-xylene as a sole carbon source. The strain was tentatively characterized as Pseudomonas putida and harboured a large plasmid (pMX) containing xyl genes involved in toluene or meta-xylene degradation pathways via an alkyl monooxygenase and a catechol 2,3-dioxygenase. This new TOL-like plasmid was stable over two hundred generations and was self-transferable. After conjugal transfer to P. putida F1, which possesses the Tod chromosomal toluene biodegradative pathway, the transconjugant P. putida F1(pMX) was able to grow on benzene, toluene, meta-xylene, para-xylene, and ethylbenzene compounds as the sole carbon sources. Catechol 2,3-dioxygenases of the transconjugant cells presented a more relaxed substrate specificity than those of parental cells (strain mX and P. putida F1).

Biodegradation, Environmental↗

PubMed1998

Effect of diseases on the culling of Holstein dairy cows in New York State.

The effect of seven diseases on culling was measured in 7523 Holstein cows in New York State. The cows were from 14 herds and had calved between January 1, 1994 and December 31, 1994; all cows were followed until September 30, 1995. Survival analysis was performed using the Cox proportional hazards model to incorporate time-dependent covariates for diseases. Different intervals representing stages of lactation were considered for effects of the diseases. Five models were fitted to test how milk yield and conception status modified the effect of diseases on culling. Covariates in the models included parity, calving season, and time-dependent covariates measuring diseases, milk yield of the current lactation, and conception status. Data were stratified by herd. The seven diseases and lactational risks under consideration were milk fever (0.9%), retained placenta (9.5%), displaced abomasum (5.3%), ketosis (5.0%), metritis (4.2%), ovarian cysts (10.6%), and mastitis (14.5%). Older cows were at a much higher risk of being culled. Calving season had no effect on culling. Higher milk yield was protective against culling. Once a cow had conceived again, her risk of culling dropped sharply. In all models, mastitis was an important risk factor throughout lactation. Milk fever, retained placenta, displaced abomasum, ketosis, and ovarian cysts also significantly affected culling at different stages of lactation. Metritis had no effect on culling. The magnitude of the effects of the diseases decreased, but remained important, when milk yield and conception status were included as covariates. These results indicated that diseases have an important impact on the actual decision to cull and the timing of culling. Parity, milk yield, and conception status are also important factors in culling decisions.

Abomasum↗

PubMed1997

Modeling the effect of a disease on culling: an illustration of the use of time-dependent covariates for survival analysis.

This study demonstrated five different approaches, with and without time-dependent covariates, to determine the effect of disease on culling. It was also of interest to determine whether the time of the disease had an effect on subsequent culling (i.e., whether disease should be treated as time-dependent covariate). To this purpose, five separate models were studied: Models 1 through 4 were Cox proportional hazards models, and Model 5 was a Weibull model. Model 1 treated disease as a binary, time-independent covariate. Model 2 treated disease as a time-dependent covariate, and one change of status was assumed to occur at the time of disease. Model 3 also assumed that one change in status occurred at the time of disease, but the effect of that change was assumed to be different depending on when the disease occurred. Models 4 (Cox) and 5 (Weibull) assumed an interaction between the occurrence of disease (time of disease) and the occurrence of culling (time of culling). As an illustration, the effect of mastitis on culling was studied for 2998 Holstein dairy cows in 10 herds. Parity and previous 305-d milk yield were also included as covariates; the data were stratified by herd. For all models, mastitis was a significant factor for culling. The significance tests for the estimates from Models 4 and 5 demonstrated that the hazard of culling differed for different stages of lactation, depending on when mastitis had occurred and when its effect on culling occurred; that is, time dependence exists between time of mastitis and time of culling.

Animals↗

PubMed1996

[Genetic determinism of sperm production in bulls].

In this study, the relationships between semen production and semen quality of Normande bulls in performance test station and in two IA centers were evaluated and the genetic characteristics and evolution of semen production of young bulls in station were calculated. When analysing the relationship between semen production of young and adult Normande bulls data from 2,677 bulls between 12 and 15 months of age exhibited large difference between 5 groups corresponding to an overall classification given by a technician. Correlations between corrected data collected in station and bull effect estimates in AZ studs were quite high for volume and concentration, and moderate for motility and number of doses per ejaculate or per month. The correlations calculated are underestimates of the true ones, as bulls with undesirable semen characteristics were culled before entering AI. Nevertheless, among the remaining bulls, important differences (40%) in semen output were observed between extreme groups, as classified by the technician. Genetic parameters evaluated from a subset of 1957 young Normande bulls confirms earlier results reported in the literature. The heritability of the average volume of the ejaculate is very high (h2 = 0.65 +/- 0.09). Sperm quality traits are moderately heritable (h2 = 0.23 +/- 0.08 for motility score to 0.37 +/- 0.09 for concentration) and strongly correlated. Total percentage of abnormal spermatozoa estimated from a selected subset seems less heritable (h2 = 0.19 +/- 0.07). A Best Linear Unbiased Prediction was then carried out on the records from 2,387 bulls using these estimates. No clear genetic trend could be detected in the population, although the phenotypic selection performed should be efficient. This apparent contradiction results from the increasing influence in the breed of one family of heavily used bull sires with a poor genetic merit on sperm production traits.

Age Factors↗

PubMed1995

Effect of disease on length of productive life of French Holstein dairy cows assessed by survival analysis.

Data from a survey performed from 1986 to 1990 were analyzed to assess the effects of diseases on length of productive life of 3589 Holstein cows from 47 herds, using a proportional hazard model. The probability of a cow being culled, or hazard function, was supposed to be the product of an unspecified baseline hazard function and log-linear, time-dependent explanatory variables that possibly influence culling rate (Cox's regression). The effect of 16 health events was studied according to lactation number of occurrence. The model included adjustments for effects of herd-year-season (considered to be random), month of calving, stage of lactation, lactation number, reproductive performance, and milk production. The probability of a cow being culled increased in early and late stages of lactation in older cows, in low producing cows, and in cows with poor reproductive performance. Mastitis before the peak of lactation or during the dry period increased the risk (relative culling rate in first lactation, 1.3 and 4.0, respectively). Teat injuries and nontraumatic udder disorders had a large impact on longevity. Cows with late metritis or early abortion had poor survival. The decrease in median length of productive life could be over a standard lactation in particular cases. Expected survivor curves, computed after assumption of a priori values of covariates and their evolution over time, appear to be powerful tools for examining the effect of health disorders on length of productive life of cows.

Animals↗

PubMed1994

Statistical analysis of length of productive life for dairy cows of the Normande breed.

The length of productive life of 103,214 Normande cows milked from 1979 to 1989 in purebred herds was analyzed using a mixed Weibull model: their probability of being culled, or hazard function, was supposed to be the product of a baseline Weibull hazard function and explanatory variables that were log-linear and time-dependent. Fixed effects that may have an impact on culling rate were successively added to the model. Two random effects, a herd-year and a sire effect, were also included. The dispersion parameter of the log-gamma prior distributions assumed for these effects was estimated maximizing a marginal posterior density obtained after algebraic integration of the corresponding random effect. The other effects and the Weibull parameter could not be integrated out easily. The probability of being culled was not changed by age at first calving but increased with stage of lactation. It also increased for low producing cows and for herds of decreasing size, especially during the 3 mo preceding the end of the period on which yearly milk production is calculated for the European Community quota system. This last phenomenon seems to be crucial for proper statistical and genetic analysis of length of productive life. The estimated variances of the herd-year and sire effects indicated a large influence of these effects on culling rate. Under certain assumptions, the standard deviation of sire effects can be assessed at > .5 expected complete lactations. This value is not reduced by consideration of differences in milk production of the cows.

Aging↗

PubMed1991

Genetic analysis of dystocia in dairy cattle.

Breeding values and genetic parameters for dystocia were estimated in Normande and Holstein breeds. Dystocia scores were related to an underlying continuous variable via a threshold model. The underlying linear model included the effects of calving season, sex of calf by parity of dam, sire of calf, grandsire of calf, dam within maternal grandsire and herd-year effects. Typical results were found for the environmental effects, with a strong influence of dam parity on dystocia, a strong influence of sex of calf, and a small effect of calving season. Herd-year variances were 32 and 40% of the residual variance in the Normande and Holstein breeds, respectively. Heritabilities for the Normande (Holstein) breed were .08 (.07) for direct effects and .11 (.07) for maternal effects. Correlations between sire and grandsire effects were .51 and .36 for the Normande and Holstein breeds, respectively. The corresponding correlations between direct and maternal effects were .15 and -.09. The results of this study show that a complete model for dystocia including the threshold concept and maternal effects can be applied for routine evaluation of dairy AI bulls. Maternal effects are important, and they should be considered in dystocia analysis, especially if nonrandom mating is present. Selection for reducing dystocia in calf and cow effects are not antagonistic.

Animals↗

PubMedDate not supplied

Genetic improvement of laying hens viability using survival analysis.

The survival of about eight generations of a large strain of laying hens was analysed separating the rearing period (RP) from the production period (PP), after hens were housed. For RP (respectively PP), 97.8% (resp., 94.1% ) of the 109,160 (resp., 100,665) female records were censored after 106 days (resp., 313 days) on the average. A Cox proportional hazards model stratified by flock (= season) and including a hatch-within-flock (HWF) fixed effect seemed to reasonably fit the RP data. For PP, this model could be further simplified to a non-stratified Weibull model. The extension of these models to sire-dam frailty (mixed) models permitted the estimation of the sire genetic variances at 0.261 +/- 0.026 and 0.088 +/- 0.010 for RP and PP, respectively. Heritabilities on the log scale were equal to 0.48 and 0.19. Non-additive genetic effects could not be detected. Selection was simulated by evaluating all sires and dams, after excluding all records from the last generation. Then, actual parents of this last generation were distributed into four groups according to their own pedigree index. Raw survivor curves of the progeny of extreme parental groups substantially differed (e.g., by 1.7% at 300 days for PP), suggesting that selection based on solutions from the frailty models could be efficient, despite the very large proportion of censored records.

Journal Article↗

PubMedDate not supplied

Relationships between type and longevity in the Holstein breed.

The relationship between type traits and longevity was studied in the French Holstein breed using a survival analysis model. In this model, the phenotypic value adjusted for systematic fixed effects, the estimated breeding value, or the residual value (defined as the difference between the adjusted phenotypic value and the estimated breeding value) of the cow for each type trait was included as a risk factor. This was done separately for two subpopulations (registered and nonregistered herds) and with or without adjustment for production traits, i.e., considering true or functional longevity. For both types of herds, udder traits (and above all, udder depth) clearly influenced the length of productive life. There seemed to be a more pronounced voluntary culling on type traits in registered herds. The correction for the within herd-year class of production traits, as a way to approximate functional longevity, increased the importance of udder traits and decreased the weight of capacity traits. The same results were obtained when the phenotypic value of the cow for type was replaced by her estimated breeding value, whereas residuals had little impact. The relationship between longevity and type traits was most often nonlinear, in particular for udder traits, but in this study, no trait with a clear intermediate optimum was found.

Animals↗