1,721,013 research outputs found
Plasma total T3 and T4 concentrations in bucks as affected by photoperiod
No full textAbstract
In order to determine whether total thyroxine (T4) and 3-3_-5-triiodothyronine (T3) plasma concentrations are affected by photoperiodic changes in bucks, these hormones were assayed using RIA in samples collected weekly for a year period in Alpine and Saanen male goats exposed to natural photoperiod (46◦N latitude, control group), or to artificial photoperiod alternating every 2 months (4M group) or 1 month (2M) with long days (16L:8D) and short days (8L:16D). In the control group, the thyroid hormones showed marked seasonal variation. Maximal monthly peaks were recorded at the beginning of spring (April) for plasma T4 (35.7±1.8 ng/ml) and in late winter to early spring (March) for plasma T3 (0.91±0.11 ng/ml)—with the lowest concentrations being recorded in October (autumn) for plasma T4 (22.8±1.0 ng/ml) and in September (late summer to early autumn) for plasma T3 (0.42±0.01 ng/ml). In the 4M group, T4 plasma concentrations varied with daylength (p < 0.05), recording an overall mean concentration significantly (p < 0.01) higher during the short days (37.3±7.5 ng/ml), than during long days (32.2±7.3 ng/ml) with a significant effect of sampling time within each photoperiod (p < 0.0001). In both lighttreated groups, T3 varied with photoperiod (p < 0.0001) and time (p < 0.0001), increasing during long days and decreasing during short days. T3 plasma concentrations (derived from peripheral monodeiodination) followed the photoperiodic changes, while it was hypothesized that the stimulatory effect of daylength on T4 (thyroid gland secretory activity) was characterized by a longer latency period and could be seen in the 4M group during the following photoperiodic treatment. It is concluded that photoperiod affects thyroid hormone plasma concentrations in male goats, since different lighting regimes resulted in different profiles of both plasma T3 and T4. Bearing in mind the pivotal role of thyroid hormones in stimulating the metabolic activity of the whole body, it is possible that the light-induced increase in circulating hormones could sustain and improve animal production. The suitability of supplementary light treatments needs to be considered.
© 2005 Elsevier B.V. All rights reserved.
Keywords: Goats; Thyroid hormones; Season; Photoperio
Melatonin concentrations vary dramatically between the two jugular veins of most individuals in sheep
No full textMelatonin concentrations vary dramatically between the two jugular veins of most individuals in shee
Plasma thyroxine and 3-3’-5’ triiodothyronine annual trends in male goats are affected by short photoperiodic cycles.
No full text
Review: Managing sheep and goats for sustainable high yield production
Full text linkThis review discusses the most relevant aspects of nutritional, reproductive and health management, the three pillars of flock efficiency, production and sustainability regarding the intensification of production in sheep and goats. In small ruminants, reproductive management is dependent on seasonality, which in turn depends on breed and latitude. Nutrition represents the major cost for flocks and greatly affects their health, the quality of their products and their environmental impact. High-yielding sheep and goats have very high requirements and dietary intake, requiring nutrient-dense diets and sophisticated nutritional management that should always consider the strong interrelationships among nutrition, immunity, health, reproduction, housing and farm management. The reproductive pattern is to a great extent assisted by out-of-season breeding, facilitating genetic improvement schemes, and more recently by advanced reproductive technologies. Heath management aims to control or eradicate economic and zoonotic diseases, ensuring animal health and welfare, food safety and low ecosystem and environmental impacts in relation to chemical residues and pathogen circulation. In highly producing systems, nutrition, genetic and hazard factors assume a complex interrelationship. Genomic and management improvement research and technological innovation are the keys to sustain sheep and goat production in the future
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Nocturnal melatonin concentrations vary dramatically between the two jugular veins in most individual sheep maintained under mimicked or natural photoperiod
No full textVariations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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