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Biomedical subjects

F Köhn

Publications and source records attributed to F Köhn.

7 recordsLinked to original sources
PubMed2007

Modeling the growth of the Goettingen minipig.

The Goettingen minipig developed at the University of Goettingen, Germany, is a special breed for medical research. As a laboratory animal it has to be as small and light as possible to facilitate handling during experiments. For achieving the breeding goal of small body size in the future, the growth pattern of the minipig was studied. This study deals with the analysis of minipig BW by modeling growth with linear and nonlinear functions and comparing the growth of the minipigs with that of normal, fattening pigs. Data were provided by Ellegaard Goettingen minipigs, Denmark, where 2 subpopulations of the Goettingen basis population are housed. In total 189,725 BW recordings of 33,704 animals collected from birth (d 0) to 700 d of age were analyzed. Seven nonlinear growth functions and 4 polynomial functions were applied. The growth models were compared by using the Akaike's information criterion (AIC). Regarding the whole growth curve, linear polynomials of third and fourth order of fit had the smallest AIC values, indicating the best fit for the minipig BW data. Among the nonlinear functions, the logistic model had the greatest AIC value. A comparison with fattening pigs showed that the minipigs have a nearly linear BW development in the time period from birth to 160 d. Fattening pigs have very low weight gains in their first 7 wk in relation to a specific end weight. After 7 wk, fattening pigs have increased growth, resulting in a growth curve that is more sigmoid than the growth curve of the minipig. Based on these results, further studies can be conducted to analyze the growth with random regression models and to estimate variance components for optimizing the strategies in minipig breeding.

Aging↗
PubMed2006

Use of repeated measures analysis for evaluation of genetic background of dairy cattle behavior in automatic milking systems.

Milking frequencies measured at official test days were used with repeated measurement analysis to reveal the environmental and genetic impact on the milking frequency of cows in automatic milking systems. Repeated measurements were 3 test-day observations per cow within days in milk (DIM) classes, with 1,216 cows in DIM class 1 (d 0 to 99), from 1,112 cows in DIM class 2 (d 100 to 199), and from 1,004 cows in DIM class 3 (d 200 to 299) kept in 15 farms. Selection criteria for models analyzing repeated measurements were Akaike and Schwarz Bayesian values, which favored the autoregressive [AR(1)] covariance structure over the compound symmetry model. Results from the AR(1) model indicated a significant impact of fixed herd and parity effects. Milking frequencies decreased with increasing parities and were greatest for first-parity cows. High daily milk yield was associated with higher milking frequencies. Heritabilities for milking frequency were 0.16, 0.19, and 0.22 in DIM classes 1, 2, and 3, respectively, from the AR(1) model. Higher heritabilities in the later stage of lactation were due to a substantial reduction of the residual variance. Genetic correlations between test-day milk yield and daily milking frequency were in the range of 0.46 to 0.57 for all DIM classes and between milking frequency and somatic cell score were near zero. For verification of results, milking frequencies of the same cows obtained from herd management programs were averaged within DIM classes. Heritabilities were slightly above the values from the AR(1) model. In conclusion, heritabilities for milking frequency in automatic milking systems are moderate enough to incorporate this behavioral trait in a combined breeding goal. The inevitable improvement of labor efficiency in dairy cattle farming demands such cows going easily and voluntarily in automatic milking systems.

Analysis of Variance↗
PubMed2001

Single-molecule spectroscopy of a dendrimer-based host-guest system.

We report on a single-molecule study of a host-guest system that consists of a second-generation polyphenylene dendrimer and the cyanine dye Pinacyanol. The use of single-molecule spectroscopy enables us to obtain more detailed information on the properties of the host-guest system and can be used to confirm solution data. At low dye to dendrimer ratios the system is present as a one-to-one complex, while for higher ratios an ion-pair system is formed. Changes in the spectral properties of the single molecules are explained by differences in local polarisability. The difference of the triplet lifetimes of single free dye molecules and of associated ones is interpreted as deriving from a larger free volume for the dye molecules in the dendritic host relative to the rigid polymer matrix.

Journal Article↗
PubMed2001

Triplet states as non-radiative traps in multichromophoric entities: single molecule spectroscopy of an artificial and natural antenna system.

Energy transfer in antenna systems, ordered arrays of chromophores, is one of the key steps in the photosynthetic process. The photophysical processes taking place in such multichromophoric systems, even at the single molecule level, are complicated and not yet fully understood. Instead of directly studying individual antenna systems, we have chosen to focus first on systems for which the amount of chromophores and the interactions among the chromophores can be varied in a systematic way. Dendrimers with a controlled number of chromophores at the rim fulfill those requirements perfectly. A detailed photophysical study of a second-generation dendrimer, containing eight peryleneimide chromophores at the rim, was performed 'J. Am. Chem. Soc., 122 (2000) 9278'. One of the most intriguing findings was the presence of collective on/off jumps in the fluorescence intensity traces of the dendrimers. This phenomenon can be explained by assuming a simultaneous presence of both a radiative trap (energetically lowest chromophoric site) and a non-radiative trap (triplet state of one chromophore) within one individual dendrimer. It was shown that an analogue scheme could explain the collective on/off jumps in the fluorescence intensity traces of the photosynthetic pigment B-phycoerythrin (B-PE) (Porphyridium cruentum). The different values of the triplet lifetime that could be recovered for a fluorescence intensity trace of B-PE were correlated with different intensity levels in the trace, suggesting different chromophores acting as a trap as function of time.

Bile Pigments↗
PubMed2000

Surgical therapy in infertile men with ejaculatory duct obstruction: technique and outcome of a standardized surgical approach.

In severe oligozoospermia or azoospermia, low ejaculate volume, low ejaculate pH and little or no fructose in seminal plasma suggest an obstruction of the seminal pathways at the level of the prostate gland, when vasal aplasia and ejaculatory disorders are excluded. We report on our standardized surgical approach in 16 consecutive patients with this condition after clinical evaluation, semen analysis, endocrine assessment, testicular biopsy and transrectal ultrasonography. Pre-operatively, sperm analysis demonstrated typical low-volume ejaculates with azoospermia in 12 and severe oligozoospermia in four cases. Ultrasonography demonstrated seven central (Müllerian) and five lateral cystic lesions. Four cases with central obstruction revealed no ultrasonographic pathology. After intra-operative vasopuncture and vasography for definite localization of the level of obstruction, transurethral incision and/or resection of ejaculatory ducts (TURED) was performed. Patency was proven in 15 out of 16 cases by 'intra-operative chromotubation'. In nine out of 12 patients, spermatozoa could be harvested intra-operatively from the vas. During the follow-up of 12 months, post-operative ejaculates showed persistent patency in six out of seven Müllerian cysts with concomitant improvement of sperm quality. Only three of the other nine cases remained patent with the worst results in lateral cystic lesions. Only two of the patients with Müllerian cysts have fathered a child so far. The data provide evidence for the effectiveness of surgical treatment of ejaculatory duct obstruction, especially in the case of central cystic lesions. The combination of surgery, cryostoring of spermatozoa retrieved intra-operatively and the possible storage of ejaculated spermatozoa post-operatively creates the possibility of subsequently using reproductive techniques if pregnancy is not achieved.

Adult↗
PubMed1999

How to structure clinical information: a practical example.

In the frame of an European telemedicine project, we have designed and implemented an Andrology server that provides the user (e.g. physicians, students) with a set of anonymized andrology cases. Within this context we faced the problem of re-structuring existing clinical information sources and gained some experience on how much of the problem might be solved by the software engineer. This paper presents a method that partially automates the maintenance of the andrology case collection. Moreover, the potential benefit of XML for information representation will be discussed.

Humans↗